Applied Thermodynamic notes

Dhanvantari College of Engineering, Nashik

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Applied Thermodynamics

SE – Mechanical

SEM – I

Basic Thermodynamic Concepts

• Thermodynamics Thermodynamics can be defined as a science that deals with the transformation of one

form of energy to the other form. For example, a. Heat energy to Mechanical energy – e.g. An I.C. engine. b. Mechanical energy to Electrical energy – e.g. A turbine generator c. Electrical energy to Mechanical energy – e.g. An Electric motor. d. Potential energy to electrical energy – e.g. A hydro-electric power plant.

Thermodynamics was mainly developed by Joule, Kelvin, Planck, Clausius, etc. It is

based on 3 laws: a) Zeroth law b) I – Law of thermodynamics c) II – Law of thermodynamics.

These laws are based on experimental results. There is no mathematical proof for

these laws of thermodynamics.

• Thermodynamics Systems “A thermodynamic system is defined as quantity of matter or region of space upon

which attention is concentrated in the analysis of the problem.” Boundary Surrounding Fig. 3.1 Thermodynamic System

Everything external to the system is called the surrounding. The system is separated from the surroundings by the system boundary as shown in Fig. 3.1. The boundary may be a real physical surface, such as the surface of the cylinder or it may be an imaginary surface enclosing some matter. The system and the surrounding together is called the Universe.

There are 3 Types of systema. Closed System (or Nonb. Open System (or Flow System)c. Isolated System.

a. Closed or Non

there is no mass transfer across the system boundary. But there may be energy transfer into and

For example, consider a system consisting of a gas, in a cylinder fitted with a piston as shown in Fig. 3.3. If the gas increases so work will be done by the gas on the piston. Thus heat and work will cross the system boundary, but since no mass crosses the boundary of the system, this system is called

b. Open system (Flow system):mass and energy can enter and leaveengineering devices are open systems. [Please see fig. on next page] For example, consider a portion of steam power plant as shown in Fig. 3.5. Mass of steam enters at section 1 and after expanding into the turbine leaves at Section 2. In this case, work is produced when the turbine is driven. So, as figure there are mass, work and heat are crossing the system boundary.


There are 3 Types of system: Closed System (or Non-flow system) Open System (or Flow System)

Closed or Non-flow system: Closed or Non flow system is of fixed there is no mass transfer across the system boundary. But there may be energy transfer into and out of the system as shown in Fig. 3.2.

For example, consider a system consisting of a gas, in a cylinder fitted with a piston as shown in Fig. 3.3. If heat is supplied to the gas, the gas expands i.e. the volume of the gas increases so work will be done by the gas on the piston. Thus heat and work will cross the system boundary, but since no mass crosses the boundary of the system, this system is called a closed system.

Open system (Flow system): Open system (Flow system) is one in which both mass and energy can enter and leave the system as shown in Fig. 3.4. Most of the engineering devices are open systems. [Please see fig. on next page]

For example, consider a portion of steam power plant as shown in Fig. 3.5. Mass of steam enters at section 1 and after expanding into the turbine leaves at Section 2. In this case, work is produced when the turbine is driven. So, as

re mass, work and heat are crossing the system boundary.


Closed or Non flow system is of fixed mass, i.e. there is no mass transfer across the system boundary. But there may be energy

For example, consider a system consisting of a gas, in a cylinder fitted with a piston heat is supplied to the gas, the gas expands i.e. the volume of

the gas increases so work will be done by the gas on the piston. Thus heat and work will cross the system boundary, but since no mass crosses the boundary of the

Open system (Flow system) is one in which both the system as shown in Fig. 3.4. Most of the

For example, consider a portion of steam power plant as shown in Fig. 3.5. Mass of steam enters at section 1 and after expanding into the turbine leaves at Section 2. In this case, work is produced when the turbine is driven. So, as shown in

re mass, work and heat are crossing the system boundary.

c. Isolated system: It is of fixed mass & energy and there is no mass or energy transfer across the system boundary. An isolated system is indepchanges that are taking place in the surroundings as shown in Fig. 3.6

• Thermodynamic Properties, Processes and Cycles Every system has certain characteristics such as Pressure, Volume, TeDensity, Internal energy, Enthalpy etc. by which its physical condition may be described. Such characteristics are called as Properties of the system. Properties may be of two types.1. Intensive Properties:

Ex. Pressure, temperature, density. 2. Extensive Properties:

the mass of the system changes, the values of the properties will change proportionately. E.g. Volume, weight, energy, enthalpy, entropy. The properties of unit mass are known as volume, specific internal energy etc. Thvalues for unit mass and they are independent of total mass, hence properties are intensive properties.


Isolated system: It is of fixed mass & energy and there is no mass or energy transfer across the system boundary. An isolated system is indep

that are taking place in the surroundings as shown in Fig. 3.6

Thermodynamic Properties, Processes and Cycles Every system has certain characteristics such as Pressure, Volume, Te

Density, Internal energy, Enthalpy etc. by which its physical condition may be described. Such characteristics are called as Properties of the system.

Properties may be of two types. Intensive Properties: They are independent of total mass in the system. Ex. Pressure, temperature, density. Extensive Properties: These are dependent on the total mass in the system. When the mass of the system changes, the values of the properties will change

y. E.g. Volume, weight, energy, enthalpy, entropy.

The properties of unit mass are known as specific properties.volume, specific internal energy etc. Thus all the specific properties indicate the values for unit mass and they are independent of total mass, hence properties are intensive properties.


Isolated system: It is of fixed mass & energy and there is no mass or energy transfer across the system boundary. An isolated system is independent of all the

that are taking place in the surroundings as shown in Fig. 3.6

Every system has certain characteristics such as Pressure, Volume, Temperature, Density, Internal energy, Enthalpy etc. by which its physical condition may be described. Such characteristics are called as Properties of the system.

They are independent of total mass in the system.

These are dependent on the total mass in the system. When the mass of the system changes, the values of the properties will change

y. E.g. Volume, weight, energy, enthalpy, entropy.

specific properties. For e.g. specific properties indicate the

values for unit mass and they are independent of total mass, hence all the specific

When all the properties of a system have definite values (such as Psystem is said to exist at a definite state, and the properties of the state are side to be functions. Any operation in which one or more properties of the system changes, is called change of state, and the series of states (i.e. sub statpassed during a change of state from state (1) to state (2) is called the Path of change of stage. The properties of all such changes of states (sub states also) are called functions.

When the path is co


When all the properties of a system have definite values (such as Psystem is said to exist at a definite state, and the properties of the state are side to be

Any operation in which one or more properties of the system changes, is called change of state, and the series of states (i.e. sub states like a, b, c etc., as shown in Fig. 3.7) passed during a change of state from state (1) to state (2) is called the Path of change of stage. The properties of all such changes of states (sub states also) are called

When the path is completely specified, the change of state is called a


When all the properties of a system have definite values (such as P1, V1, T1), then the system is said to exist at a definite state, and the properties of the state are side to be State

Any operation in which one or more properties of the system changes, is called es like a, b, c etc., as shown in Fig. 3.7)

passed during a change of state from state (1) to state (2) is called the Path of change of stage. The properties of all such changes of states (sub states also) are called Path

mpletely specified, the change of state is called a Process.

First Law of Thermodynamics

• Introduction In the last chapter, we have studied, work, heat, temperature, pressure etc. and in this chapter we will be studying the interrelation between work and heat i.e. the first law of Thermodynamics.

• I- law For a Closed System Undergoing a Cycle or Joules

Joule carried out experiment in 1843, which led to the formulation of the IThermodynamics. He took a known insulated adiabatically from the surroundings. The vessel was and a thermometer as shown in Fig. 4.1.

Now let certain amount of work Wwheel. The quantity of work can be measured by the fall of weighpaddle wheel. Let t1 be the work transfer let the temperature rise to t(1) to state (2) and the process 1

Now, let the insulation be interact by heat transfer (i.e. heat will be dissipated from the system to the surroundings) till the system comes to the original temperature tsystem during the process 2

The system thus undergoes a cycle, which consists of a definite amount of work input W1-2 to the system, followed by a heat transfer Q


f Thermodynamics

In the last chapter, we have studied, work, heat, temperature, pressure etc. and in this chapter we will be studying the interrelation between work and heat i.e. the first law of

law For a Closed System Undergoing a Cycle or Joules Experiment

Joule carried out experiment in 1843, which led to the formulation of the IThermodynamics. He took a known quantity of water in a rigid vessel, which was insulated adiabatically from the surroundings. The vessel was fitted with a paddle wheel and a thermometer as shown in Fig. 4.1.

Now let certain amount of work W1-2 be done upon the closed system by the paddle wheel. The quantity of work can be measured by the fall of weight W, which drives the

be the initial temperature of water before the work transfer and after work transfer let the temperature rise to t2. So, the system is changing its state from state (1) to state (2) and the process 1-2 undergone by the system is shown in Fig. 4.2.

Now, let the insulation be removed. Then the system and the surroundings will interact by heat transfer (i.e. heat will be dissipated from the system to the surroundings) till the system comes to the original temperature t1. The amount of heat transfer Qsystem during the process 2-1 can be estimated (Q2-1 = m Cp T).

The system thus undergoes a cycle, which consists of a definite amount of work to the system, followed by a heat transfer Q2-1 from the system.


In the last chapter, we have studied, work, heat, temperature, pressure etc. and in this chapter we will be studying the interrelation between work and heat i.e. the first law of

Experiment

Joule carried out experiment in 1843, which led to the formulation of the I-law of quantity of water in a rigid vessel, which was

with a paddle wheel

be done upon the closed system by the paddle W, which drives the

initial temperature of water before the work transfer and after . So, the system is changing its state from state

2 undergone by the system is shown in Fig. 4.2.

removed. Then the system and the surroundings will interact by heat transfer (i.e. heat will be dissipated from the system to the surroundings) till

. The amount of heat transfer Q2-1 from the

The system thus undergoes a cycle, which consists of a definite amount of work from the system.


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Joule repeated this experiment for different weights & for different heights and in each case he found that, net work transfer during a cycle is proportional to the net heat transfer, i.e.

∑ δ W � ∑ δ Q

or in other words, “when a closed system undergoes any cyclic process, the cyclic integral of work is proportional to the cyclic integral of heat.” This is known as the I law of thermodynamics for a closed system undergoing a cycle.

� � � � � t

� � � � � � In S. I. units J = 1

� � � � �

Thus the I law states the general principle of conservation of energy i.e. energy can neither be created nor be destroyed, but energy can be converted from one form to the other.

• I-low For a Closed System Undergoing a Process If a closed system undergoes a change of state or a process, and during which both

work transfer and heat transfer are involved, then the net energy transfer will be stored within the system. If ‘Q’ is the amount of heat transferred to the system and ‘W’ is the amount of work transferred from the system during the process as shown in Fig. 4.3, then the net energy transfer (Q-W) will be stored in the system.

W Energy in storage is neither heat nor work but is

Called as Internal energy or simple energy of the system.

Q Fig. 4.3 Q – W = ∆ E

or Q = ∆ E + W

Where ∆ E is the change in energy.

Here Q, W and ∆ E all are expressed in Joule.

• Energy a Property of The System Consider a system which changes its state from state (1) to state (2) by following the path ‘A’ and returns from state (2) to state (1) by following path ‘B’ as shown in Fig. 4.4. So the system undergoes a cycle. Now writing the I law for the Path A, QA – WA = ∆ EA …. (1)

System

and for the path ‘B’

The processes 1-A-2 and 2 i.e. Total work transfer during the cycle = Total heat transfer during cycle. i.e. WA + WB = Qor WB + WB = QA

or (QB - WB) = QA from (1) (2) and (3)

- EB =

i.e. EA = - Similarly, if the system returns from state (2) to (1) by following the path ‘C’ instead of path ‘B’, then i.e. EA - EC from (4) and (5), EB = EC

Thus the change in energy for the path B and C are same. Hence change in energy does not depend upon path, so it depends on end states. Hence it is a point function and since properties are point functions,

• Different Forms of Stored Energies The total energy ‘E’ is made up of kinetic energy, Potential energy and Internal energy. E = K.E. + P.E. + I.E.Kinetic energy is due to the motion of the fluid in the system.Potential energy is the energy due to the A part of the total energy, which is stored in the molecular and atomic structure is knows as Internal energy and is denoted by U.K. E. = 0 and P.E. = 0,


and for the path ‘B’

QB – WB = EB …. (2) 2 and 2-B-1 together constitute a cycle for which

i.e. Total work transfer during the cycle = Total heat transfer during cycle.

= QA + QB

A + QA

- WA from (1) (2) and (3)

= EA

EB …. (4) Similarly, if the system returns from state (2) to (1) by following the path ‘C’ instead of

…. (5)

…. (6)

Thus the change in energy for the path B and C are same. Hence change in energy does not depend upon path, so it depends on end states. Hence it is a point function and since properties are point functions, energy is a property of the system.

rms of Stored Energies The total energy ‘E’ is made up of kinetic energy, Potential energy and Internal

E = K.E. + P.E. + I.E. Kinetic energy is due to the motion of the fluid in the system. Potential energy is the energy due to the gravitational force. A part of the total energy, which is stored in the molecular and atomic structure is knows as Internal energy and is denoted by U. K. E. = 0 and P.E. = 0,


1 together constitute a cycle for which

i.e. Total work transfer during the cycle = Total heat transfer during cycle.

Similarly, if the system returns from state (2) to (1) by following the path ‘C’ instead of

Thus the change in energy for the path B and C are same. Hence change in energy does not depend upon path, so it depends on end states. Hence it is a point function and

.

The total energy ‘E’ is made up of kinetic energy, Potential energy and Internal

A part of the total energy, which is stored in the molecular and atomic structure is knows


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E = U and the I – law for the process Q = ∆ E + W (1) becomes Q = ∆ U + W (2) In the differential form, equation (1) and (2) becomes, � Q = dE + � W i.e. � Q = dE + PdV …. (3) � Q = dU + � W i.e. � Q = dU + PdV …. (4) When K.E. and P.E. are considered, then the I – law for a processes will be � Q = �W + dU + d (K.E.) + d (P.E.) …. (5) In the integrated form equation (5) becomes

Q1-2 – W1-2 = U2 – U1 + ��

�

��

��

�� mg (Z2 – Z1) …. (6)

Where ‘C’ is the velocity and ‘Z’ is the height for unit mass.

q – w = u2 – u1 + ��

��

��

�� (Z2 – Z1) …. (7)

• Internal Energy (U) “It is the energy stored in the molecular structure due to heat and work interactions”. OR In case of gases we known that, the gas is made up of a number of molecules, which are moving continuously. I.E. is the energy which arises from the motion of these molecules. If the temperature of the gas is increased, the molecular activity increases therefore the I.E. also increases. (Thus I.E. is a function of temperature & its value can be increased or decreased) by adding or removing heat to or from the system. Due to practical difficulties is the very very difficult to determine the absolute value of Internal energy. Fortunately, in most of the thermodynamic applications, change in I.E. is used since changes in states of a system is considered. Change in I.E. is denoted by ∆ U and ∆ U = U2 – U1. For unit mass, ∆ u = u2 – u1

• Enthalpy (H) It is an extensive property, since its value depends on mass. Enthalpy of substance is given by the sum of Internal energy and Pressure – Volume product. i.e.

H = U + PV

& specific enthalpy,

h = u + Pv

• Specific Heat “Specific heat of a gas is defined as the amount of heat required to rise the temperature of unit mass of a gas through one degree.” Let C = General specific heat Q = Heat transfer (J) ∆ T = Change in temperature in ‘K’ m = mass in kg


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Then from the definition

C = �

�. ∆ � …. (1)

�units will be

��.��

Or

Q = m . C. ∆ T ....(2)

In the differential form,

� q = C . dT ….. (3)

& for unit mass

� q = C . dT ….. (4)

Or

C = � �

�� ….. (5)

There are two specific heats

1) Specific heat at constant volume Cv 2) Specific heat at constant Pressure Cp

• Specific Heat At Constant Volume Cv “It is the amount of heat required to rise the temperature of unit mass of a gas through one degree, when the volume is kept constant.” If a unit mass of a gas is taken in a closed vessel and is heated, the volume of the gas remains constant, but the temperature increases. As the volume remains constant, there is no external work done by the gas, and as temperature of the gas increases, there is increase in internal energy of the gas. Therefore, heat supplied to the gas is completely utilised in increasing the I.E. of the gas.

Cv =��

� ��

��

��

�

Fig. 4.5 ‘Cv’ is also defined as the rate of change of specific internal energy with respect to temperature when the volume is kept constant.

Unit mass of a

gas at const.

volume

• Specific Heat At Constant Pressure, C“It is the amount of heat required to rise the temperature of unit mass of a gas through one degree, when the pressure is kept constant.”

Where as in case of constant heating, the heat supplied is completely utilised for increasing I.E.

Specific heat at constant pressure is greater than specific heat at constant volume. i.e. Cp > Cv

& Cp =

‘Cp’ is also defined as the rate of change of specific enthalpy with respect to temperature when the pressure is kept constant.

• Adiabatic Index ( )

It is the ratio of specific heat at constant volume and is given by,

or k =

Note: For air Cp = 1.005

and = 1.4

• Perpetual Motion of First Kind (PMM I – law states the general principle of conversion of energy, i.e. energy can neither be created nor be destroyed but it can be transformed from one form to the other.


Specific Heat At Constant Pressure, Cp “It is the amount of heat required to rise the temperature of unit mass of a gas

ugh one degree, when the pressure is kept constant.”

Consider a unit mass of a gas in a cylinder fitted with a frictionless piston as shown in Fig. 4.6. When the gas is heated, the piston moves up, maintaining the same pressure. But the volume and temperature of the gas increases during heating. As there is increases in volume, there is external work done by the gas and as there is increase in temperature, there is increase in I.E.

Thus heat supplied, when the pressure is constant, is utilised for two purposes.

1) To do some external work 2) To increase the I.E. of the gas,

Where as in case of constant heating, the heat supplied is completely utilised for

Specific heat at constant pressure is greater than specific heat at constant volume.

’ is also defined as the rate of change of specific enthalpy with respect to temperature when the pressure is kept constant.

It is the ratio of specific heat at constant pressure to the specific heat at constant

Perpetual Motion of First Kind (PMM -1) law states the general principle of conversion of energy, i.e. energy can neither be

nor be destroyed but it can be transformed from one form to the other.


“It is the amount of heat required to rise the temperature of unit mass of a gas

onsider a unit mass of a gas in a cylinder fitted with a frictionless piston as shown in Fig. 4.6. When the gas is heated, the piston moves up, maintaining the same pressure.

gas increases during heating. As there is increases in volume, there is external work done by the gas and as there is increase in temperature, there

Thus heat supplied, when the pressure is constant, is

Where as in case of constant heating, the heat supplied is completely utilised for

Specific heat at constant pressure is greater than specific heat at constant volume.

’ is also defined as the rate of change of specific enthalpy with respect to

pressure to the specific heat at constant

law states the general principle of conversion of energy, i.e. energy can neither be nor be destroyed but it can be transformed from one form to the other.

But PMM – 1 is defined as a machine which will produce continuous work output, without receiving any energy from any other system or the surroundings (Ref. Fig. 4.7.)

It will created energy and thus violates I law of thermodynamics. All the attempts made so for to make such PMM-1 us just a conceptual machine.

Converse of PMMcontinuously consume work, without producing some other form of energy (Fig. 4.8.)

• Second Law Of I Law• Limitation of I Law

1. The expression, equal to heat transfer. It does not specify whether the process is possible in forward direction or backward direction.

2. It is also partically found that, all forms of energies are not equally convertwork and the first law is silent about the extent of conversion of energy. So, it becomes necessary to study the second Law.

• Heat Engine and Heat Engine Cycle Heat engine is an engine, which converts heat energy into mechanical energy. Heat engine works on Heat engine cycle. A heat engine cycle is a thermodynamic cycle, in which there is a net heat transfer to the system and a net work As we have studies, Heat engines are broadly classified into 2 types,

1. External combustion engines.2. Internal combustion engines.


1 is defined as a machine which will produce continuous work output, without receiving any energy from any other system or the surroundings (Ref. Fig. 4.7.)

It will created energy and thus violates I law of thermodynamics. All the attempts made so for to make such a machine have failed, thus they show the validity of I law. Thus

1 us just a conceptual machine.

Converse of PMM-1 is also true, i.e. there can be no machine which would continuously consume work, without producing some other form of energy (Fig. 4.8.)

Second Law Of I Law Of Thermodynamics

Q, merely states that, work transfer during a cycle is equal to heat transfer. It does not specify whether the process is possible in forward direction or backward direction. It is also partically found that, all forms of energies are not equally convert

and the first law is silent about the extent of conversion of energy. So, it becomes necessary to study the second Law.

Heat Engine and Heat Engine Cycle Heat engine is an engine, which converts heat energy into mechanical energy. Heat

engine works on Heat engine cycle. A heat engine cycle is a thermodynamic cycle, in which there is a net heat transfer to the system and a net work transfer from the system.

studies, Heat engines are broadly classified into 2 types, External combustion engines. Internal combustion engines.

Figure 5.1 shows a simple steam power plant. In this plant an amount of heat “Qsupplied from the furnace (Also calledtemperature reservoir) to the water in the boiler drum. An amount of heat ‘Qlow temperature reservoir, like a coolant in the condenser, and in doing so, an amount of work ‘W’ will be produced.

The thermal efficiency, engine is defined as,


1 is defined as a machine which will produce continuous work output, without receiving any energy from any other system or the surroundings (Ref. Fig. 4.7.)

It will created energy and thus violates I law of thermodynamics. All the attempts a machine have failed, thus they show the validity of I law. Thus

an be no machine which would continuously consume work, without producing some other form of energy (Fig. 4.8.)

Q, merely states that, work transfer during a cycle is equal to heat transfer. It does not specify whether the process is possible in forward

It is also partically found that, all forms of energies are not equally convertible into and the first law is silent about the extent of conversion of energy. So, it

Heat engine is an engine, which converts heat energy into mechanical energy. Heat engine works on Heat engine cycle. A heat engine cycle is a thermodynamic cycle, in

transfer from the system. studies, Heat engines are broadly classified into 2 types,

Figure 5.1 shows a simple steam power plant an amount of heat “Q1” is

supplied from the furnace (Also called as High to the water in the boiler

amount of heat ‘Q2’ is rejected to the low temperature reservoir, like a coolant in the condenser, and in doing so, an amount of work

The thermal efficiency, of the heat


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��

��

��

��

��

��

��

��

��

�� 1 �

��

��

In case of I.C. Engines combustion of air and fuel takes place inside the engine cylinder. The products of combustion will be directly acting on the pistons of the I.C. Engines for producing the power.

Now consider an I.C. Engine as shown in Fig. 5.2

Q1 Let Qi : is the heat transferred to the system.

W1 Q2 : is the heat transferred from the system. W1 : is the work done by the system W2 W2 : is the work done on the system. Q2 Then,

Fig. 5.2 Net heat transfer in a cycle

= Qnet = Q1 – Q2 and

Net work transfer in a cycle = Wnet = W1 – W2.

According to the I – law of thermodynamics,

� � � � � � Q,

or Wnet = Qnet

We can write,

W1 – W2 = Q1 – Q2

• II – Law of Thermodynamics Because of the limitations, of I – law, it becomes necessary to study the second law. There are two important statements of Second law, they are 1. Kelvin Planck statement 2. Clausius statement

1. Kelvin Planck statement: “It is impossible for a heat engine to produce net work

in a cycle, if it exchanges heat with a single reservoir.”

OR “Heat engine cannot produce work output, if it exchanges heat with a single

reservoir”.

We have seen that,

But practical experience it is noted that total heat supplied cannot be converted into useful work ‘W’ i.e. Q1 there has to be heat rejection i.e. Q Therefore, for a heat engine to produce net work in a cycle, it has to exchange with two reservoirs.

But if, O2 = 0, then Qin a complete cycle by exchanging heat with only Planck’s statement. Such a heat engine is called a second kind (PMM-2). A attempts made so far to make such a machine havKelvin Planck’s statement.

2. Clausius Statement: We know that, heat always flows from a hot body to a cold body. The reverse process never occurs by itself.

Clausius statement is given as operating in a cycle, will produce no effect other than transfer of heat from a low temperature body to a high temperature body”.

OR

“Heat cannot flow by itself, from a cold body to a hot body, in order to achieve this some work must be expended.”

Example – Refrigerator: In this case heat is removed from the cold body ‘A’ and transferred to the atmosphere but by consuming work input ‘W’.


We have seen that,

But practical experience it is noted that total heat supplied cannot be converted into W i.e. a heat engine can never be 100% efficient. But W < Q

rejection i.e. Q2 > 0

Therefore, for a heat engine to produce net work in a cycle, it has to exchange

= 0, then Q1 W or , the heat engine will produce net work in a complete cycle by exchanging heat with only one reservoir, thusPlanck’s statement. Such a heat engine is called a Perpetual Motion Machine of the

2). A PMM-2 is impossible and it is just a conceptual engine. All the attempts made so far to make such a machine have failed, thus they show the validity of Kelvin Planck’s statement.

Clausius Statement: We know that, heat always flows from a hot body to a cold body. The reverse process never occurs by itself.

Clausius statement is given as “It is impossible to construct a device, which operating in a cycle, will produce no effect other than transfer of heat from a low temperature body to a high temperature body”.

“Heat cannot flow by itself, from a cold body to a hot body, in order to achieve must be expended.”

Refrigerator: In this case heat is removed from the cold body ‘A’ and transferred to the atmosphere but by consuming work input ‘W’.


But practical experience it is noted that total heat supplied cannot be converted into W i.e. a heat engine can never be 100% efficient. But W < Q1,

Therefore, for a heat engine to produce net work in a cycle, it has to exchange heat

, the heat engine will produce net work one reservoir, thus it violates Kelvin Perpetual Motion Machine of the

2 is impossible and it is just a conceptual engine. All the e failed, thus they show the validity of

Clausius Statement: We know that, heat always flows from a hot body to a cold

construct a device, which operating in a cycle, will produce no effect other than transfer of heat from a low

“Heat cannot flow by itself, from a cold body to a hot body, in order to achieve

Refrigerator: In this case heat is removed from the cold body ‘A’ and

• Equivalence of Kelvin Planck and Clausius Statements1. Kelvin Planck’s statement:

heat with two reservoirs.2. Clausius statement:

order to achieve this some work must At first sight these two statements will appear to be, two different statements and are

unconnected. But it can be easily shown that, these are the two parallel statements of II law and are equivalent in all respects.

The equivalence of the two statements wiof one statement results into the violation of the other.

(a) Violation of Clausius statement leads into the violation of Kelvin Planck’s statement: Consider a cyclic heat pump ‘P’, which transfers heat from a at ‘t1’ without consuming work into (i.e. W = 0) thus violating Clausius statement. Now let us assume a cyclic heat engine

Violation of Kelvin Planck statement lead

Clusius statement

•


Equivalence of Kelvin Planck and Clausius Statements Kelvin Planck’s statement: “For a heat engine to produce Wnet

heat with two reservoirs.” Clausius statement: “Heat cannot flow by itself from a cold body to a hot body. In order to achieve this some work must be expended.”

first sight these two statements will appear to be, two different statements and are unconnected. But it can be easily shown that, these are the two parallel statements of II law and are equivalent in all respects.

equivalence of the two statements will be proved, if we prove that the violation of one statement results into the violation of the other.

Violation of Clausius statement leads into the violation of Kelvin Planck’s

Consider a cyclic heat pump ‘P’, which transfers heat from a ’ without consuming work into (i.e. W = 0) thus violating Clausius statement.

Now let us assume a cyclic heat engine ‘E’ which also operates between

the same two reservoirs at ‘trespectively. The rate of working theis such that, it draws an amount of heat ‘QHTR equal to that discharged by the heat pump. Then the HTR may be eliminated and heat Qdischarged by the heat pump may be directly fed to the heat engine. So, the heat pump ‘P’ and heat engine ‘E’ acting together will form a heat engine, operating in cycles and producing net work by exchanging heat with one reservoir. This violates the Kelvin Planck statement.

Violation of Kelvin Planck statement leads into the violation of

statement:

Let us consider a PMM-2 (E), which produces Wa cycle by exchanging heat with only one reservoir at ‘t1’ and thus violates Kelvin Planck’s statement (ref. fig.)

Now let us assume cyclic heat pump ‘P’ heat Q2 from LTR at ‘t2’ and supplying heat to HTR at ‘t1’ by consuming work ‘W’ equal to that PMM supplies in a complete cycle. So, ‘E’ and ‘P’ together will form a heat pump and producing the complete effect of transferring heat from LTR tany external aid.


net, it has to exchange

“Heat cannot flow by itself from a cold body to a hot body. In

first sight these two statements will appear to be, two different statements and are unconnected. But it can be easily shown that, these are the two parallel statements of II

ll be proved, if we prove that the violation

Violation of Clausius statement leads into the violation of Kelvin Planck’s

Consider a cyclic heat pump ‘P’, which transfers heat from a LTR at ‘t2’ to HTR ’ without consuming work into (i.e. W = 0) thus violating Clausius statement.

which also operates between

the same two reservoirs at ‘t1’and ‘t2’ respectively. The rate of working the heat engine is such that, it draws an amount of heat ‘Q1’ from HTR equal to that discharged by the heat pump. Then the HTR may be eliminated and heat Q1 discharged by the heat pump may be directly fed to the heat engine. So, the heat pump ‘P’ and heat

acting together will form a heat engine, operating in cycles and producing net work by exchanging heat with one reservoir. This violates the Kelvin Planck statement.

s into the violation of

2 (E), which produces Wnet in a cycle by exchanging heat with only one reservoir at

’ and thus violates Kelvin Planck’s statement (ref.

Now let us assume cyclic heat pump ‘P’ extracting ’ and supplying heat to HTR at

’ by consuming work ‘W’ equal to that PMM – 2 supplies in a complete cycle. So, ‘E’ and ‘P’ together will form a heat pump and producing the complete effect of transferring heat from LTR to HTR, without

• Quasi-Static Process/Reversibility and Irreversibility Quasi – means nearly or almost. So, Quasiprocess or a process which proceeds with extreme slowness. A quasiproceeds from one equilibrium state to another equilibrium state till the end of the process. All the states passed through by the system, during the process are all equilibrium state.

A quasi-static process is represented on the PVand if we carry out the process in the reverse direction, then it is possible to retrace the same path. Hence it is known as

Where as in case of Irreversible process, only end states are equilibrium states and all the intermediate states are nondotted curved as shown.

Conditions of Reversibility (or Factors making the process Irrversible.)

1. A process should be quasi2. There should be no friction.3. Both the system and

process in reversed.

• Entropy We have studied the I

definition of a derived property known as Internal energy. Analysis of IInd law will lead to definition of another derived property Clausius discovered that, when a small amount of heat ‘

which is at a absolute temperature T, then it will undergo a process, & the ratio

for all reversible processes. He assigned the value

Q meaning transformation. Thus, when a small amount of heat ‘transformed to a system, the entropy changes by an amount ‘dS’. This change in entropy is regarded as the transformation content of the system.

Fig. 5.12 Note that entaddition of heat and it decreases with the removal of heat.

System

at ‘T’


Static Process/Reversibility and Irreversibility means nearly or almost. So, Quasi-static process means nearly static

process or a process which proceeds with extreme slowness. A quasione equilibrium state to another equilibrium state till the end of the

process. All the states passed through by the system, during the process are all

static process is represented on the PV-diagram by a continuous curand if we carry out the process in the reverse direction, then it is possible to retrace the same path. Hence it is known as Reversible process.

Where as in case of Irreversible process, only end states are equilibrium states states are non-equilibrium states and is represented by a means of a


A process should be quasi-static. There should be no friction. Both the system and the surroundings should restore their initial state after the process in reversed.

We have studied the I-law of thermodynamics. Analysis of I-law leads to the definition of a derived property known as Internal energy. Analysis of IInd law will lead to definition of another derived property – the Entropy.

Clausius discovered that, when a small amount of heat ‘ Q’ is supplied to a system,

which is at a absolute temperature T, then it will undergo a process, & the ratio

for all reversible processes. He assigned the value = dS and called ‘S’ as

The term entropy is taken from the Greek words ‘tropee’ meaning transformation. Thus, when a small amount of heat ‘transformed to a system, the entropy changes by an amount ‘dS’. This change in entropy is regarded as the transformation content of the system. Note that entropy is a thermodynamic property, it increases with the addition of heat and it decreases with the removal of heat.


static process means nearly static process or a process which proceeds with extreme slowness. A quasi-static process

one equilibrium state to another equilibrium state till the end of the process. All the states passed through by the system, during the process are all

diagram by a continuous curve and if we carry out the process in the reverse direction, then it is possible to retrace the same

Where as in case of Irreversible process, only end states are equilibrium states equilibrium states and is represented by a means of a


the surroundings should restore their initial state after the

law leads to the definition of a derived property known as Internal energy. Analysis of IInd law will lead to

is supplied to a system,

which is at a absolute temperature T, then it will undergo a process, & the ratio is same

= dS and called ‘S’ as entropy.

Greek words ‘tropee’ meaning transformation. Thus, when a small amount of heat ‘ Q’ is transformed to a system, the entropy changes by an amount ‘dS’. This change in entropy is regarded as the transformation content of the

ropy is a thermodynamic property, it increases with the addition of heat and it decreases with the removal of heat.

• Clausius Theorem

It states that, the cyclic integral of

• Entropy – a Property To prove this, we have to prove that the change of entropy does not depend upon path but it depends upon end sates. Then, we will able to say that, entropy is a property of the system. Consider a system, which changes its state from state point following the reversible path ‘a’ and returns from state point (2) to state point (1) by following the reversible path ‘b’. Then the two paths 1

a

(Note: may be read as integral

Since path ‘b’ is reversible.

a

The magnitude of

depend upon the path. So, it depends upon the end states, hence it is point function and we know that properties are point

• Clausius Inequality We know that, from Clausius theorem,

for a reversible cycle.

But for a irreversible cycle,

Combining results for reversible and irreversible cycles we can write,

This expression is known as Clausius Inequality. It implies reversible, irreversible or impossible.


It states that, the cyclic integral of for a reversible cycle is equal to zero. i.e.

Property To prove this, we have to prove that the change of entropy does not depend upon path

but it depends upon end sates. Then, we will able to say that, entropy is a property of the

Consider a system, which changes its state from state point (1) to state point (2) by following the reversible path ‘a’ and returns from state point (2) to state point (1) by following the reversible path ‘b’.

Then the two paths 1 – a – 2 and 2 – b – 1 together will form a cycle. Now from Clausius theorem,

(1 – a – 2 – b – 1). The above integral may be replaced as the sum of two integrals one for the path ‘a’ other for the path ‘b’.

(Note: may be read as integral for the reversible path 1

a

Since path ‘b’ is reversible.

The magnitude of (i.e. ‘dS’) is same for the paths ‘a’ and ‘b’ and it does not

depend upon the path. So, it depends upon the end states, hence it is point function and we know that properties are point-functions, hence it is a property of the system.

We know that, from Clausius theorem,

for a reversible cycle.

But for a irreversible cycle,


This expression is known as Clausius Inequality. It implies whether any cyclic process in reversible, irreversible or impossible.


for a reversible cycle is equal to zero. i.e.

To prove this, we have to prove that the change of entropy does not depend upon path but it depends upon end sates. Then, we will able to say that, entropy is a property of the

(1) to state point (2) by following the reversible path ‘a’ and returns from state point (2) to state point (1) by

1 together will form a cycle.

The above integral may be replaced as the sum of two integrals one for the path ‘a’ other for the path ‘b’.

for the reversible path 1 – a – 2)

(i.e. ‘dS’) is same for the paths ‘a’ and ‘b’ and it does not

depend upon the path. So, it depends upon the end states, hence it is point function and we functions, hence it is a property of the system.


whether any cyclic process in


Page | 17

• Ideal Gases & Ideal Gas Processes

• Definition An ideal gas is one, which obeys all the gas laws and the characteristic gas equation PV = mRT, at all temperatures and Pressures. But actually there is no perfect or Ideal gas in reality. But all the real gases like Air, O2, H2, N2, He behave as ideal gas, at very low pressures and high temperatures.

• Gas laws The behaviour of ideal gas governed by certain laws which are known as gas laws viz.

1. Boyle’s law 2. Charle’s law 3. Avogadro’s law 4. Characteristic gas equation or equation of state.

1. Boyle’s law: Boyle experimentally established that, The volume of a given mass of a

gas is inversely proportional to the absolute pressure, when the temperature is constant.

i.e. V � �

�, when T = C

� V = �

�

or PV = C where C is a constant. Also P1 V1 = P2 V2 = C Consider a gas in a cylinder fitted with a frictionless piston. Let the initial properties be P1 and V1. Now when the gas is heated at constant temperature, then the gas expands and the pressure falls to P2 and volume increases to V2. This is represented on PV-diagram as shown in fig. 2. Charle’s Laws: i) It states that, “when the pressure of a given mass of a gas is kept

constant, then volume is directly proportional to the absolute temperature” i.e. when P = C, then V � T or V = CT or

�

�� C

or

��

��

�� C

ii) It also states that, “when the volume of a given mass of a gas is kept constant, the pressure is directly proportional to the absolute temperature”

i.e. P � T when V = C


Page | 18

or

P = CT

�

�� C

or

��

��

�� C

• Equation of State or Characteristic Gas Equation In engineering practice, pressure, volume temperature all very simultaneously. So, Boyle’s law or Charle’s law alone is not applicable, since one of the three properties is kept constant. In order to establish a relationship between these three properties, Boyle’s law and Charle’s laws are combined together, which gives a general equation called characteristic gas equation. According to Boyle’s law,

V � �

� when T = C …. (1)

And according to Charle’s law, V � T when P = C …. (2) It is obvious that,

V is � to T and �

�

i.e. V � �

� …. (3)

or PV � T or PV = CT where ‘C’ is a constant

or ��

�� C …. (4)

or in general

��

��

��

�� ..... = C

or since v = specific volume in ��

�

Then equation will be,

��

�� C …. (5)

When 1 kg of gas is condensed, then the constant for the equation (4) is written as ‘R’ and is called Characteristic gas constant.

� �

�� R …. (6)

Now consider ‘m’ kg of gas. Multiply both sides of equation (6) by ‘m

�. � .�

�� m . R

m. v = V = Total volume

� PV = mRT This is known as characteristic-equation of an ideal gas.


Page | 19

Note that the value of ‘R’ for air = 0.287 ��

��

• Universal Gas Constant Frequently it is required to express the equation of state, PV = mRT on mole basis. The mass of a substance ‘m’ is equal to the product of number of moles ‘n’ and the molecular weight ‘M’ i.e. m = n . M Hence substituting the value of ‘m’ in equation (1) we get, PV = n . M . RT …. (2) Now the molal specific volume is defined as the volume / unit mole and is denoted by v�,

� v� � �

�

Hence equation (2) becomes. P v� = MRT …. (3) Now if we consider two gases, ‘a’ and ‘b’ occupying equal molal volumes at the

same temperature and pressure, equation (3) becomes, Pa . v�a = Mb . Rb . Tb & Pb . v�b = Mb . Rb . Tb According to Avogadro’s law, perfect gases at the same temperature and pressure,

occupy the same molal volume. i.e. v�a = v�b when Pa = Pb and Ta = Tb, We have,

�� .��

�� .��

��

� Ma . Ra = Mb . Rb = M . R The product ‘M . R’ is called the Universal Gas constant and it is denoted by R� � Equation (3) can be written as,

P v� = MRT P v� = R� T

and equation (2) can be written as PV = n MRT PV = n R� T

and The value of R� for air = 8.3143 ��

� ��


Page | 20

• Relationship Between Cp and Cv for an Ideal Gas Specific heat at constant pressure and specific heat at constant volume, we have studied in the I – law of thermodynamic. Since Cp and Cv are the properties of a system, there is a relationship between these. We know that, specific enthalpy ‘h’ is given by, h = u + Pv dh = du + d (P . v) ….. (1) from the definitions of

Cp = � �

� ��

��

��

�

� dh = Cp . dT …. (2) and

Cv = � �

� ��

� ��

��

� du = Cv . dT …. (3) Since Pv = RT d (Pv) = d (RT) d (Pv) = R . dT, since R is a constant …. (4) Substituting equations (2), (3) and (4) in (1) we get, Cp . dT = Cv dT + R . dT � Cp = Cv + R (Since dT is common in both sides) or …. (5)

We also know that the ratio ��

�� γ

� Cp = γ . Cv Substituting in Cp – Cv = R we get, γ . C � C � R Cv (� � 1) = R

…. (6)

and since

Cp = γ . C,

…. (7)

Cp – Cv = R

C � �

��

C� � �. �

��

• Constant Volume Process

(a) Work done We know that, work done in a nonHere V = C dV = 0 W1-2

(b) Heat supplied

(c) Change of Entropy

Hence from equation (6) (i.e. from II

s2

s2 – s1


Constant Volume Process During this process, volume remains constant (V = C) and is represented on a PVby means of a vertical line as shown. When a unit mass of a gas a heated in a closed (i.e. V = C), then, since volume remains constant, no external work is done. But since temperature of the gas increases I.E. increases.

We know that, work done in a non-flow system = dV = 0

2 = 0

We know that, from the I-law for a closed system undergoing a process, Q = U + W In this case since W = 0Q = U

or q = u

q = du = Cv. dT from the definition of Cv. for total mass, = dU = m . Cv . dT

Here v1 = v2 hence In = In 1 = 0

Hence from equation (6) (i.e. from II-law and Entropy chapter)

Fig. 6.2 (c)

– s1 = Cv In

Unit

mass of

gas

1 = Cv In


During this process, volume remains constant (V = C) and is represented on a PV-diagram by means of a vertical line as shown.

a unit mass of a gas a heated in a closed vessel (i.e. V = C), then, since volume remains constant, no external work is done. But since temperature of the gas

law for a closed system undergoing a

In this case since W = 0

. for total mass, Q

and from equation (9) i.e.

s2 – s1

• Constant Pressure Process During this process pressure remains constant (P = C) and this process is represented by means of a horizontal line on the P V

When a unit mass of a gas it taken in a cylinder fitted with a frictionless piston and is heated. Then the piston moves up maintaining same the gas increases, the work is done by the gas on the piston. As the temperaincreases, Internal Energy increases. So, heat supplied in a constant pressure heating process is utilised for 2 purposes.

i) For doing some external work.ii) For increasing the I.E. of the gas.a) Work done

We know that, Work done in a

W1 – 2 = P

Here the law for the process is P = C

W1 – 2 = P

W1-2 = P (V

s2 –


and from equation (9) i.e.

1 = Cp In

Constant Pressure Process During this process pressure remains constant (P = C) and this process is

represented by means of a horizontal line on the P V – diagram as shown.

When a unit mass of a gas it taken in a cylinder fitted with a frictionless piston and is heated. Then the piston moves up maintaining same pressure (i.e. P = C). As the volume of the gas increases, the work is done by the gas on the piston. As the temperaincreases, Internal Energy increases. So, heat supplied in a constant pressure heating process is utilised for 2 purposes.

For doing some external work. For increasing the I.E. of the gas.

We know that, Work done in a non-flow system

= P

Here the law for the process is P = C

= P

= P (V2 – V1)

s1 = Cv In


During this process pressure remains constant (P = C) and this process is diagram as shown.

When a unit mass of a gas it taken in a cylinder fitted with a frictionless piston and is pressure (i.e. P = C). As the volume of

the gas increases, the work is done by the gas on the piston. As the temperature of the gas increases, Internal Energy increases. So, heat supplied in a constant pressure heating process


Page | 23

If the pressure P is in �

�� and volume is in m3 then the resultant unit of

Work will be N-m or J.

b) Change in Internal Energy (∆U) = U2 – U1

c) Heat transferred. From then I – law, Q – W = ∆ U Q = ∆U + W

or δQ � dU � δW δQ � dU � P dV δQ � dU � d�PV since P = C δQ � d�U � PV δQ � dH or δ q � dh

i.e. heat supplied = change in enthalpy.

d) Change in Entropy

Here P1 = P2 � In ��

��

= In 1 = 0; Hence from equations which are in terms of

pressure ratio (From I law and Entropy chapter)

i.e. from equation (9),

s2 – s1 = Cp In �

�

and from equation (10),

s2 – s1 = Cp In ��

��

• Isothermal Process During this process, temperature remains constant (T = C). The law for the process is PV = C and is represented by means of a curve as shown on the PV-diagram. It is represented by means of a horizontal line on T-S diagram. a) Work done

We know that. Work done in a non-flow system

W1 – 2 = � P . dv�

�

The law for the process is PV = C i.e. PV = P1 V1 = C

� P � ��

�

� W1 – 2 = � ��

�

�

�. dV


Page | 24

= P1 V1 � ��

�

�

�

b) Change in IE dU = m Cv dT = 0 as T = C, dT = 0

c) Heat transferred From the first law for a closed system undergoing a process, Q = ∆ U + W � Q = d U + � W � Q = 0 + �w

� Q = �W = P1 V1 In �

�

= P1 V1 In ��

��

d) Change of entropy

Here T1 = T2 � In ��

��

= In 1 = 0

Hence from equations which are in terms of temperature ratio, i.e. from equation (6) (from II haw and entropy chapter}

s2 – s1 = R In �

�

and from equation (10)

s2 – s1 = - R In ��

��

s2 – s1 = R In ��

��

• Polytropic Process (PVn = C) a) Work done

We know that, the work done in non-flow system, W1-2 = � PdV ….. (1) But for a polytropic process, P Vn = P1 V

n1 = P2 V

n = C

� P = �

��

Substituting in equation (1), we get,

W1 – 2 = � �

��

�

� dV

W1 – 2 = � CV��

�dV

= C ��

��

�

= C ��

��

�

W1 – 2 = P1 V1 In �

�

W1 – 2 = P1 V1 In ��

��


Page | 25

= � ��

��

� ��

= � ��

��

� ��

��

� ��

Substituting for C

= ��

�� .��

–��

� .��

–��

= ��

��

��

W1-2 = ��

�� or

��

�� ….. (2)

Since P1 V1 = m R T1 and P2 V2 = m R T2

W1-2 = ��

�� ….. (3)

b) Heat supplied From the I-law for a closed system under going a process, Q = ∆ U + W For unit mass, q = ∆ u + w In the differential from. � q = du + �w � q = du + P �w

q1-2 = Cv (T2 – T1) +� ��

�� from equation (3).

= �C � �

�� T2 �T1

= ��

�� T� � T��

since Cp – Cv = R

= ��

�� T� � T��

taking Cv common, we can write,

q1-2 = Cv ��

�� T� � T� , as

�

�

� �

q1-2 = Cn . �T� � T�� where Cn = Cv . ��

�� is known as Polytropic specific heat. ….. (5)

(d) Change in Entropy

For equation (4)

q = ��

�� Cv . �T� � T��

In the differential form,

� q = ��

�� Cv . dT

Since � �

�� ds

ds =

or

s2 – s1 = Cv

This is the change in entropy, for unit mass in a Polytropic process in terms of

temperature ratio. Note:

1. Change in entropy in terms of volume ratio is given by,

Note:

2. Change in entropy in terms of

Work done, W

=

=

b) Heat supplied

Here Heat supplied = 0 (Since neither heat enters nor leaves the system during the process).

c) Change in entropy for a reversible adiabatic processAs we have studied during a reversible adiabatic process, entropy remains constant (S = C) and the process is called as Isentropic process. Since S = C, dS = 0 change in entropy is zero.

s2 – s1 = . R . In

s2 – s1 = .


ds = Cv .

Cv .

v .In . …. (6)


Change in entropy in terms of volume ratio is given by,

….. (7)

Change in entropy in terms of pressure ratio is given by,

v) Adiabatic process ( = C)

During this process neither heat enters the system nor heat leaves the system.

a) (Note: Derivation is just similar to work done in polytropic process, put in place of n).

Work done, W1-2 =

Here Heat supplied = 0 (Since neither heat enters nor leaves the system during the

Change in entropy for a reversible adiabatic process As we have studied during a reversible adiabatic process, entropy remains constant (S = C) and the process is called as Isentropic process. Since S = C, dS = 0 change in

. R . In

. . In


…. (6)


….. (7)

During this process neither heat enters the system nor heat

Work done (Note: Derivation is just similar to work done in polytropic

Here Heat supplied = 0 (Since neither heat enters nor leaves the system during the

As we have studied during a reversible adiabatic process, entropy remains constant (S = C) and the process is called as Isentropic process. Since S = C, dS = 0 change in


Page | 27

• Steam • Introduction

Water is the most readily available substance on the Earth. So, the steam which is nothing but water in the gaseous state is being used since old days for various thermodynamic functions. In this chapter we will study various terms related with steam, its properties and different processes.

• Terms Related With Steam 1. Pure substance: It is single substance, which retains the same molecular structure

and chemical composition during the process of energy transfer.

A pure substance exists in all the three phases viz solid, liquid, or gaseous. Water is an example of pure substance, since it exists in all the three phases and in all the three phases its molecular structure is same.

2. Evaporation Process: When the heat is supplied to the liquid, it changes its phase to gaseous state and is known as evaporation.

So, when the heat is added to the water, it gets converted into steam.

3. Saturation temperature: At any certain pressure the phase change occurs at particular temperature and is known as saturation temperature. For e.g. Saturation temperature of water at 1 atmosphere (i.e. 1 bar) pressure is 100o C.

Saturation temperature corresponding to phase change from liquid to gas is known as Boiling point. So, boiling point of water at 1 atm is 100o C; while boiling point of water at 10 atm pressure is 180o C. Note that the boiling point temperature increases with pressure.

4. Sub cooled liquid: The liquid having temperature below saturation temperature is known as sub cooled liquid. For e.g. water at 1 atm pressure and 80o C.

5. Saturated liquid: The liquid at saturation temperature (boiling point is known as saturated liquid. For e.g. Water at 1 atm and at 100o C.)

6. Sensible heat of liquid: Heat supplied to liquid, which is having temperature below saturation temperature. The sensible heat causes change in temperature of liquid. Finally the liquid attains saturation temperature. The relationship between heat added and temperature change is given by, Q = m . Cp . ∆ T = m Cp (T1 – T2) When the heat is added at constant pressure, we can write, H = Q = m . Cp . ∆ T Where Cp is specific heat and for water, Cpw = 4.187 KJ/Kg –K.

7. Saturated vapour: Vapour at saturation temperature is known as Saturated vapour. For e.g. steam at 1 atm and 100oC


Page | 28

8. Latent heat of evaporation: Amount of heat required to convert 1 kg of liquid from saturated liquid state to saturated vapour state is known as Latent heat. Latent heat also depends on pressure, i.e. it decreases with pressure for e.g. latent

heat of water at 1 atm pressure is 2258 ��

�� and at 10 atm pressure is 2013

��

��

9. Critical point: As the pressure increases, latent heat of evaporation decreases. The

pressure corresponding to 0 ��

�� latent heat is known as Critical point.

For water Critical point pressure is 221.2 bar and Critical point temperature is 374.15o C

10. Wet steam: The steam at any state between saturated liquid and saturated vapour state is known as Wet steam. In this state, there are suspended water particles in suspension. Thus the steam is a mixture of liquid and vapour. As the heat is added, these suspended particles also gets evaporated and finally giving saturated or dry steam.

11. Dryness fraction: This is the number which represents the quality of steam. It gives percentage of vapour present in the steam. If mv = mass of vapour in the given mass of steam, and m1 = mass of vapour in the given mass of steam. Then the dryness fraction ‘x’ can be obtained by

x = ��

��

For e.g. a. In saturated liquid, there is no vapour present hence mv = 0. So, x = 0. b. In saturated c. For the states between saturated liquid and saturated vapour, the steam is a mixture

of liquid and vapour. So 0 < x < 1. At State 1. There is 75% liquid and 25% vapour, so x = 0.25 State 2. 50% liquid and 50%, vapour, So x = 0.5 State 3. 25% liquid and 75%, vapour, x = 0.75

12. Superheated steam: The steam having temperature above saturated temperature is known as superheated steam. 13. Degree of superheat: For superheated steam difference between its temperature and corresponding saturation temperature is known as Degree of superheat. So degree of superheat = tsup - tset. 14. Sensible heat of vapour: The heat added to the vapour, which causes change in temperature is known as sensible heat of vapour. The relation between sensible heat of vapour and change in temperature in given by,

Q = m . Cp . ∆ T = m . Cpvap (tsup - tsat) For water,


Page | 29

Cpvap = 2.1 ��

�� at 1 atm pressure.

• Properties of Steam The reference point for calculation of properties of steam is taken at 0o C. The properties of steam at any state are calculated using two different tables viz

1. Saturated water and steam tables. 2. Properties of superheated steam tables.

Saturated water and steam table: This table gives the properties of saturated water and saturated steam for different saturation temperature of pressure. The table is in the following form,

Saturation Temperature

Saturation Abs. Pressure

Sp. Volume Specific Enthalpy Specific Entropy

oC (T) bar (P) Vf Vg hf hfg hg Sf Sg

20 0.0233 0.001 57.83 83.86 2454.3 2538.2 0.2963 8.66 50 0.1233 0.001 12.046 209.26 2382.9 2592.2 0.7035 8.077 100 1.0133 0.001 1.673 419.06 2256.9 2676.0 1.3069 7.355

Thus from this table we can directly obtain the values of properties viz. specific volume, specific enthalpy and specific entropy at any saturation temperature or pressure. The properties of saturated water are denoted by the letter suffixed with ‘f’ as vf, hf & sf. While the properties of saturated steam are denoted by letter suffixed with ‘g’ as vg, hg and sg. Some times the value ‘enthalpy of evaporation’ or latent heat of evaporation is also directly given which is denoted by ‘hfg’. If not given the value o ‘hfg’ can be calculated as (‘hg - hf’) In order to obtain the properties of steam at any other than saturated water or saturated steam sloes, the following procedure is used. 1.Consider the point representing the state of steam on a constant pressure line. 2.Obtain the properties of saturated water and saturated steam at that pressure from the

steam table. 3.Then using following co. relations calculated the properties of the desired state.

• Steam Calorimeters The exact condition of steam cannot be determined only from the knowledge of pressure and temperature if the steam is wet. To find out the quality of steam i.e. its dryness fraction, steam calorimeters are used. They are of the following types:

(i) Throttling Calorimeter (ii) Separating Calorimeter (iii) Combined separating and throttling calorimeter

• Throttling Calorimeter Throttling occurs when a gas or steam passes through a fine orifice. As no external work is done by the steam in passing through a fine orifice the specific enthalpy of steam is same after throttling as before. But as pressure falls down after throttling, the liquid enthalpy reduces after throttling. This fact is made use in this calorimeter.

From the above discussion it is clear that if high pressure, sufficiently dry steam is throttled then it tends to become superheated.

Fig. 7.11 gives the arrangement of the the main by a sampling tube. The sampling tube helps in taking a correct representative sample of the steam. It consists of no. of holes which take steam from various levsteam main i.e. upper level having more dry steam and lower level having heavy wet steam.

This steam is then lead to the throttling chamber through a stop value and pressure gauge. In the chamber throttling occurs in a throttle orifice. The stecondenser. The temperature of throttled steam (superheated) is noted by a thermometer placed in an oil pocket. The pressure is measured by a water manometer, because small variations can be easily noted. The dryness fraction is ca

Let,

P1 = Pressure of steam before throttling measured by the pressure gauge.

P2 = Pressure of steam after throttling measured by the manometer.

tsup = temperature of steam (superheated) after throttling.

ts2 = temperature of saturate

x1 = Dryness fraction of steam.

Then

Enthalpy before throttling = Enthalpy after throttling

hf1 + x1 h

x1 =


From the above discussion it is clear that if high pressure, sufficiently dry steam is throttled then it tends to become superheated.

Fig. 7.11 gives the arrangement of the throttling calorimeter. Steam is drawn through the main by a sampling tube. The sampling tube helps in taking a correct representative sample of the steam. It consists of no. of holes which take steam from various levsteam main i.e. upper level having more dry steam and lower level having heavy wet steam.

This steam is then lead to the throttling chamber through a stop value and pressure gauge. In the chamber throttling occurs in a throttle orifice. The steam is then exhausted to a condenser. The temperature of throttled steam (superheated) is noted by a thermometer placed in an oil pocket. The pressure is measured by a water manometer, because small variations can be easily noted. The dryness fraction is calculated as follows:

= Pressure of steam before throttling measured by the pressure gauge.

= Pressure of steam after throttling measured by the manometer.

= temperature of steam (superheated) after throttling.

= temperature of saturated steam corresponding to P2

= Dryness fraction of steam.

Enthalpy before throttling = Enthalpy after throttling

hfg1 = hf2 + Cp = h2 [Tsup – Ts2]


From the above discussion it is clear that if high pressure, sufficiently dry steam is

throttling calorimeter. Steam is drawn through the main by a sampling tube. The sampling tube helps in taking a correct representative sample of the steam. It consists of no. of holes which take steam from various levels in the steam main i.e. upper level having more dry steam and lower level having heavy wet steam.

This steam is then lead to the throttling chamber through a stop value and pressure am is then exhausted to a

condenser. The temperature of throttled steam (superheated) is noted by a thermometer placed in an oil pocket. The pressure is measured by a water manometer, because small

lculated as follows:

= Pressure of steam before throttling measured by the pressure gauge.

= Pressure of steam after throttling measured by the manometer.

An important point to note is that this

gets superheated after throttling. Another precaution to be taken during the test is that the stop value must be fully opened to avoid any partial throttle in it.

Thus its limitations can be listed as

1. Complete separation of water is not possible and hence cannot be used for steam with high dryness fraction.

2. The result obtained is not very accurate. Limitations of throttling calorimeter

In order to assure that steam after throttling is superheated, superheat is required. This process is shown on hthen t2 = 105o C. The throttling process shown by a dotted line 1 line P1 at 1.

The quality of steam xmeasured simply by throttling. For example take steam at point 1’ with dryness fraction xAfter throttling to P2 = 1 atm the superheat is less than 5taken at point 1” with dryall.

Thus if only throttling calorimeter is to be used the entering steam should have minimum dryness fraction, so that the final condition of steam is superheated. If the steam has dryness fraction below this minimum value, the quality of this steam can not be measured by the throttling calorimeter alone. This is the limitations of the throttling calorimeter.

Therefore if steam is very wet initially and pressure Psteam into the superheated region then combined separating and throttling calorimeter is used for the measurement of quality.


An important point to note is that this calorimeter can be used only for steam which gets superheated after throttling. Another precaution to be taken during the test is that the stop value must be fully opened to avoid any partial throttle in it.

Thus its limitations can be listed as

eparation of water is not possible and hence cannot be used for steam with high dryness fraction. The result obtained is not very accurate.

Limitations of throttling calorimeter

In order to assure that steam after throttling is superheated, superheat is required. This process is shown on h-s diagram by points 1 and 2. If P

C. The throttling process shown by a dotted line 1 – 2 intersects the pressure

The quality of steam x1 at point 1 is the minimum dryness fraction that can be measured simply by throttling. For example take steam at point 1’ with dryness fraction x

= 1 atm the superheat is less than 5oC. If initial condition of steam is taken at point 1” with dryness fraction equal to x1” the final condition gives no superheat at

Thus if only throttling calorimeter is to be used the entering steam should have minimum dryness fraction, so that the final condition of steam is superheated. If the steam

ss fraction below this minimum value, the quality of this steam can not be measured by the throttling calorimeter alone. This is the limitations of the throttling

Therefore if steam is very wet initially and pressure P2 is not low enough to tasteam into the superheated region then combined separating and throttling calorimeter is used for the measurement of quality.


calorimeter can be used only for steam which gets superheated after throttling. Another precaution to be taken during the test is that the

eparation of water is not possible and hence cannot be used for steam

In order to assure that steam after throttling is superheated, minimum 5o C of s diagram by points 1 and 2. If P2 is 1 atm

2 intersects the pressure

the minimum dryness fraction that can be measured simply by throttling. For example take steam at point 1’ with dryness fraction x1.

C. If initial condition of steam is ” the final condition gives no superheat at

Thus if only throttling calorimeter is to be used the entering steam should have minimum dryness fraction, so that the final condition of steam is superheated. If the steam

ss fraction below this minimum value, the quality of this steam can not be measured by the throttling calorimeter alone. This is the limitations of the throttling

is not low enough to take the steam into the superheated region then combined separating and throttling calorimeter is

• Separating CalorimeterFor analyzing steam which remains wet even after throttling, the throttling

calorimeter cannot beThe separating calorimeter is used for finding dryness fraction of low quality or

fairly wet steam.

The principle on which it operates consists of changing direction of wet separately so that the heavier water particles get accurately measured in a collecting chamber. Thus it is known as a separating known as a separating calorimeters and is a mechanical device.

Such a calorimeter is illustrated diagrammatically in Fig. 7.13. An entrysteam into a perforated up which is suspended in the collector tank. A calibrated gauge glass is fitted to the side of the tank. An exit is provided for the dry steam near the top of the tank. A drain valve is provided at the bottom.

Now, in operation steam is taken into the calorimeter from a steam main through a sampling tube. This steam is forced to rapidly change its direction by means of perforated cup. The heavier water particles get separated out and fall through he perforations in the collector tank. The level of this collected water is given by the gauge glass. The dry steam which passes through the exit is condensed by a small condenser. The dryness fraction is found as follows:

Let, M = mass of dry steam condensed

m = mass of w

then dryness fraction, x =


Separating Calorimeter For analyzing steam which remains wet even after throttling, the throttling

calorimeter cannot be used. The separating calorimeter is used for finding dryness fraction of low quality or

The principle on which it operates consists of changing direction of wet separately so that the heavier water particles get separated and the accumulated mass can be accurately measured in a collecting chamber. Thus it is known as a separating known as a separating calorimeters and is a mechanical device.

Such a calorimeter is illustrated diagrammatically in Fig. 7.13. An entrysteam into a perforated up which is suspended in the collector tank. A calibrated gauge glass is fitted to the side of the tank. An exit is provided for the dry steam near the top of the tank. A drain valve is provided at the bottom.

eration steam is taken into the calorimeter from a steam main through a sampling tube. This steam is forced to rapidly change its direction by means of perforated cup. The heavier water particles get separated out and fall through he perforations in the

llector tank. The level of this collected water is given by the gauge glass. The dry steam which passes through the exit is condensed by a small condenser. The dryness fraction is

Let, M = mass of dry steam condensed

m = mass of water collected in tank

then dryness fraction, x =


For analyzing steam which remains wet even after throttling, the throttling

The separating calorimeter is used for finding dryness fraction of low quality or

The principle on which it operates consists of changing direction of wet steam separated and the accumulated mass can be

accurately measured in a collecting chamber. Thus it is known as a separating known as a

Such a calorimeter is illustrated diagrammatically in Fig. 7.13. An entry pipe feeds steam into a perforated up which is suspended in the collector tank. A calibrated gauge glass is fitted to the side of the tank. An exit is provided for the dry steam near the top of the tank.

eration steam is taken into the calorimeter from a steam main through a sampling tube. This steam is forced to rapidly change its direction by means of perforated cup. The heavier water particles get separated out and fall through he perforations in the

llector tank. The level of this collected water is given by the gauge glass. The dry steam which passes through the exit is condensed by a small condenser. The dryness fraction is

Care must be taken that the set up is adequately warmed up, so that condensation of

steam does not occur. Otherwise this will give wrong readings. Also the dry steam must not be allowed to come in contact with the water which has been already separated out, or else condensation occurs.

Here the separating calorimeter approximately dries out the steam by separating out heavier water particles. This nearly dry steam then passes to the throttling calorimeter. Here the steam gets superheated. A small condenser is provided after the throttlinThe arrangement is as shown in Fig. 7.14. The dryness fraction is calculated as given below.

Let, M = mass of steam which is condensed.

m = mass of water separated in the separating calorimeter.

x1 = dryness fraction of s

=

x2 = dryness fraction of throttling calorimeter.

x = total dryness fraction of steam.

Now, moss of saturated steam through throttling calorimeter = x

This is actually the total dry saturated steam in the

Total steam bled = M + m

Now, Dryness fraction

x =

x = x1 x2


Care must be taken that the set up is adequately warmed up, so that condensation of steam does not occur. Otherwise this will give wrong readings. Also the dry steam must not

ome in contact with the water which has been already separated out, or else

Here the separating calorimeter approximately dries out the steam by separating out heavier water particles. This nearly dry steam then passes to the throttling calorimeter. Here the steam gets superheated. A small condenser is provided after the throttlinThe arrangement is as shown in Fig. 7.14. The dryness fraction is calculated as given below.

Let, M = mass of steam which is condensed.


= dryness fraction of separating calorimeter

= dryness fraction of throttling calorimeter.

x = total dryness fraction of steam.

Now, moss of saturated steam through throttling calorimeter = x2

This is actually the total dry saturated steam in the steam under test

Total steam bled = M + m

Dryness fraction


Care must be taken that the set up is adequately warmed up, so that condensation of steam does not occur. Otherwise this will give wrong readings. Also the dry steam must not

ome in contact with the water which has been already separated out, or else

Here the separating calorimeter approximately dries out the steam by separating out heavier water particles. This nearly dry steam then passes to the throttling calorimeter. Here the steam gets superheated. A small condenser is provided after the throttling calorimeter. The arrangement is as shown in Fig. 7.14. The dryness fraction is calculated as given below.


M

steam under test

• Vapour Power Cycles• Introduction:

The steam power plant is one of the most successful energy into mechanical work. The main elements of a vapour power cycle are boiler, turbine, and condenseratomic fission is used to vaporize water into steam in the bexpended in the turbine adiabatically to produce work output. Vapour leaving the turbine then enters the condenser where heat is removed until the vapour is condensed into liquid state. Saturated liquid is delivered to a pump whersaturation pressure corresponding the boiler pressure and liquid is delivered to the boiler where the cycle repeat itself. The working fluid (water) goes through a cyclic process called vapour cycle also called Ranking cycle, scycle for steam power plant. The vapor power cycle is perhaps the most widely used thermal cycle for the production of electrical energy in the world.

• Rankine cycle: The schematic arrangement and the cycle on Tideal cycle does not involve any internal irreversibility’s and consists of the following four processes occurring in the respective elements of the cycle.

Process:4.5: Isenstropic compression of water in pump. Process: 5.1.2 : Heat addition at constant pressure in the boiler. Process: 2.3: Insentropic expansion in the turbine Process: 3.4: Heat rejection at constant pressure in the condenser.

Water enters the pump at the state 4 as isentropically to the saturation pressure of the boiler. The vertical distance between state 4 and 5 on the T-s diagram is g Water enters the boiler as a compressed liquid at state 5 and leaves as a superheated vapour at state 2. The boiler is basically a large heat exchanger where the heat originating from combustion of fuel, nuclear reactorsat constant pressure. The boiler together


Vapour Power Cycles

The steam power plant is one of the most successful systems for conversation of heat energy into mechanical work. The main elements of a vapour power cycle are boiler,

and condenser and feed pump. Heat energy released by combustion of fuel or by atomic fission is used to vaporize water into steam in the boiler. The vapour is then expended in the turbine adiabatically to produce work output. Vapour leaving the turbine then enters the condenser where heat is removed until the vapour is condensed into liquid state. Saturated liquid is delivered to a pump where its pressure raised to the saturation pressure corresponding the boiler pressure and liquid is delivered to the boiler where the cycle repeat itself. The working fluid (water) goes through a cyclic process called vapour cycle also called Ranking cycle, suggested by Rankine and is the ideal cycle for steam power plant. The vapor power cycle is perhaps the most widely used thermal cycle for the production of electrical energy in the world.

The schematic arrangement and the cycle on T-s diagram is shown in fig. 3.1. The ideal cycle does not involve any internal irreversibility’s and consists of the following four processes occurring in the respective elements of the cycle.

Isenstropic compression of water in pump. Heat addition at constant pressure in the boiler.

Insentropic expansion in the turbine Heat rejection at constant pressure in the condenser.

Water enters the pump at the state 4 as saturated liquid and is compressed isentropically to the saturation pressure of the boiler. The vertical distance between state 4

s diagram is generally exaggerated for clarity. Water enters the boiler as a compressed liquid at state 5 and leaves as a superheated

vapour at state 2. The boiler is basically a large heat exchanger where the heat originating from combustion of fuel, nuclear reactors, or other source is transferred to water at constant pressure. The boiler together with the section where the st


for conversation of heat energy into mechanical work. The main elements of a vapour power cycle are boiler,

and feed pump. Heat energy released by combustion of fuel or by oiler. The vapour is then

expended in the turbine adiabatically to produce work output. Vapour leaving the turbine then enters the condenser where heat is removed until the vapour is condensed

e its pressure raised to the saturation pressure corresponding the boiler pressure and liquid is delivered to the boiler where the cycle repeat itself. The working fluid (water) goes through a cyclic process

uggested by Rankine and is the ideal cycle for steam power plant. The vapor power cycle is perhaps the most widely used

s diagram is shown in fig. 3.1. The ideal cycle does not involve any internal irreversibility’s and consists of the following

is compressed isentropically to the saturation pressure of the boiler. The vertical distance between state 4

Water enters the boiler as a compressed liquid at state 5 and leaves as a superheated vapour at state 2. The boiler is basically a large heat exchanger where the heat originating

, or other source is transferred to water essentially the steam is superheated


Page | 35

(the superheater) is often called the steam generator. The process of formation of steam from 5 to 2 occurs at constant pressure (5-1-2 is constant pressure line) The superheated vapour at state 2 enters the turbine where it expands isentropically and produces work by rotating the shaft connected to an electric generator. The pressure and temperature of steam drop to state 3 where steam enters the condenser. At this state, steam is usually a saturated vapour liquid maxture with a high quality (dryness fraction). Steam is condensed at constant pressure in the condenser, which is basically a large heat exchanger, by rejecting heat to a cooling medium such as a lake, a river, or the atmosphere through cooling water in cooling tower. Steam leaves the condenser as saturated liquid at state 4 and enters the pump, completing the cycle. Remembering that the area under the process curver on a T-s diagram represents the heat transfer for internally reversible processes, the area undera the process 5-1-2 represents the heat, transferred to the water in the boiler and the area under the curve 3-4 represents the heat rejected in the condenser. The difference between thewe two for area enclosed by the cycle is the net work produced during the cycle. It is evieent without calculation that the efficiency of this cycle will be less than that of the carnot cycle for the same limits of temperature, because all the heat supplied is not at upper constant temperature. Water at lower temperature is mixed with higher temperature water in the bhoiler, making the processes irreversible. It is also evident that net work output per unit mass of steam is greater in the Rankine cycle. In follows that steam consumption is less and work ratio is greater in Rankine Cycle. (More details about Carnot and Rankine cycles are explained in Applied Thermodynamics – I by the same author).

• Energy Analysis of Rankine Cycle: If an energy balance is preformed on each of these components, the steady flow energy equation, neglecting the changes in potential and kinetic energy is q = ∆ h + w Where q is specific heat transfer in the component, ∆h is the change in enthalpy across the component, and w is the specific work done by the component, all in kJ per kg. Since the processes in the boiler and condenser are isobaric, the ideal work in these components is zero ws = - � vdp and dp = 0. Then energy equation reduces to q = ∆h Since the compression and expansion processes in the pump and turbine are

adiabatic processes (q = 0), the energy equation reduces to w = - ∆h ��

��

Now the pump work is

wp = - � wdp �

�= - v4 (P5 – P4)

��

��

The turbine work is

wT = - ∆h = - (h3 – h2) = (h2 – h3) ��

��

Net work of the cycle = wT – wp ��

��

= = (h2 – h3) – v4 (p5 – p4) ��

��

Heat supplied, q = (h2 – h5) ��

��

But h5 = h4 + wp


Page | 36

� q = h2 – h4 – wp ��

��

The thermal efficiency of the simple cycle is η��

��

��

As compared to the enthalpies involved the magnitude of pump work is small,

therefore pump work can be neglected, then

η��

��

• Comments on Rankine cycle: The important operating limitation for any vapour cycle using water as the working

fluid is the moisture content of the steam at the turbine exhaust. The turbine outlet steam is usually at a very, very low pressure, which means that the density is also extremely low. This low steam density produces a very high velocity in the low-pressure part of the turbine. If there are any moisture droplets in this steam, they can actually erode the leading edge of the low pressure turbine blades like raindrops erode the surface of the earth. This condition is likely to be server it the moisture content of the steam at the turbine exhaust exceeds 10 percent.

• Methods to improve thermal efficiency of Rankine cycle: The thermal efficiency of the simple steam or Rankine cycle can be improved by

increasing the maximum steam temperature (the vapour superheat), by increasing the maximum system pressure Pmaxi and or by increasing the condenser vacuum. (decreasing the minimum system pressure). Increasing the superheat of the steam increases the specific work of the cycle and decreases the moisture content of the steam at the turbine exhaust. Increasing the maximum pressure may increase the specific work if the same temperature is maintained but always increases the moisture content at the turbine exhaust. Lowering the maximum steam pressure increases the specific work of the cycle, but it also increases the moisture content at the turbine exhaust. Steam power plants are responsible for the production of most of the electric power in the world and even small increase in thermal efficiency can mean large saving of fuel requirements. Therefore every effort is made to improve the efficiency of the cycle on which steam power plant operates. The basic idea behind all the modification is the information obtained from Carnot cycle i.e. to increase the thermal efficiency of power cycle, increase the average temperature at which heat transferred to the working fluid in the boiler, or decrease the average temperature at which heat is rejected from the working fluid in the condenser. That is average temperature of fluid should be as high as possible in the boiler and as low as possible in the condenser. Also for steam saturation temperature are related to saturation pressure.

• Lowering the Condenser Pressure:Lowering the operating pressure of the condenser automatically lowers the

temperature of the steam and thus the temperature at which heat is rejected. The effect of lowering the condenser pressure on the Rankine cycle is shown on T3.2 For comparison purpose the turbine inlet state is kept the same. The hatched area on this diagram represents the condenser pressure from PWhich is very small. the thermal efficiency of the cycle. However there is a lower limit on the condenser pressure that can be used. It to the temperature of the cooling medium.

Lowering the condenser pressure is not without any side effect as it increases the moisture content of the steam at the last stage of the turbine. The presence of large quantity of moisture contents is highly efficiency and erodes the turbine blades. Air leakage in the condenser increases which increases the work of air extraction pump in condensing plant.

• Superheating: The average temperature at which heat is added to the steam can be increased without

increasing the boiler pressure buy superheating the steam to high superheating on the performance is shown in fig. 3.3 (a) on Tefficiency and steam consumption against steam temperature at turbine entry


Lowering the Condenser Pressure: Lowering the operating pressure of the condenser automatically lowers the

temperature of the steam and thus the temperature at which heat is rejected. The effect of condenser pressure on the Rankine cycle is shown on T

or comparison purpose the turbine inlet state is kept the same. The hatched area on this diagram represents the increase in the net work output as a result of lowering the

ser pressure from P3 to P3’. The heat input also increase by the area under 55’. Thus overall effect of lowering condenser pressure is an increase in

the thermal efficiency of the cycle. However there is a lower limit on the condenser pressure that can be used. It cannot be lower than the saturation pressure corresponding

ature of the cooling medium.

Lowering the condenser pressure is not without any side effect as it increases the moisture content of the steam at the last stage of the turbine. The presence of large quantity of moisture contents is highly undesirable in turbine beacasue it decreases the turbine

the turbine blades. Air leakage in the condenser increases which increases the work of air extraction pump in condensing plant.

The average temperature at which heat is added to the steam can be increased without increasing the boiler pressure buy superheating the steam to high temperature. Thesuperheating on the performance is shown in fig. 3.3 (a) on T-s diagram and iefficiency and steam consumption against steam temperature at turbine entry


Lowering the operating pressure of the condenser automatically lowers the temperature of the steam and thus the temperature at which heat is rejected. The effect of

condenser pressure on the Rankine cycle is shown on T-s diagram in Fig.

or comparison purpose the turbine inlet state is kept the same. The hatched area on increase in the net work output as a result of lowering the

’. The heat input also increase by the area under 55’. Thus overall effect of lowering condenser pressure is an increase in

the thermal efficiency of the cycle. However there is a lower limit on the condenser cannot be lower than the saturation pressure corresponding

Lowering the condenser pressure is not without any side effect as it increases the moisture content of the steam at the last stage of the turbine. The presence of large quantity

turbine beacasue it decreases the turbine the turbine blades. Air leakage in the condenser increases which

The average temperature at which heat is added to the steam can be increased without temperature. The effect of

s diagram and in (b) the cycle efficiency and steam consumption against steam temperature at turbine entry

The hatch area on the diagram represents the increase in the net work. The total area under the curve 22 represents the increase in the heat input. Thus both the network and heat input increases as a result thermal efficiency, since the average temperature at which heat is added incrSuperheating the steam has another desirable effect, that the moisture content of the steam at exit of steam decreases as can be seen from the Tat 3). The presence of water during the expansion is undesirerode the turbine blade.

The temperature to which steam can be superheated is limited by metallurgical considerations. Presently steam temperature allowed at turbine inlet is 620very promising materials in this regard. For given boiler and condenser pressure as the superheat temperature increases the cycle efficiency increases and the specific steam consumption decreases as shown in fig. 3.3(b).

• Increasing the Boiler Pressure: The average temperature during the heat addition process can be increased by increasing the operating pressure of the boiler which automatically raises the temperature of boiling. This in turn raises the average temperature at which heat is aincreases the thermal efficiency. The effect of increasing shown on T-s diagram in Fig. 3.4(a) and steam cycle efficiency and specific steam consumption against boiler pressspecific enthalpy of evaporation decreases thus less heat is added at the maximum cycle temperature Efficiency first increases with boiler pressure initially due to maximum cycle temperature being raised but then decreases by lowering of the mean temperature at which heat is added. Therefore the graph of efficiency rises, reaches maximum and then falls. The turbine inlet temperature is kept same in both cases and notice that for a fixed turbine inlet temperature, the cycle shifts to the left and the moisture content of steam at boiler exit increases. This undersirable effects can be corrected using reheating discussed in the next section.


The hatch area on the diagram represents the increase in the net work. The total area the curve 22 represents the increase in the heat input. Thus both the network and heat

input increases as a result of superheating the steam. The overall effect is an increase in thermal efficiency, since the average temperature at which heat is added incrSuperheating the steam has another desirable effect, that the moisture content of the steam at

it of steam decreases as can be seen from the T-s diagram (the quality at 3’ is higher than presence of water during the expansion is undesirable since these water particles

The temperature to which steam can be superheated is limited by metallurgical considerations. Presently steam temperature allowed at turbine inlet is 620very promising materials in this regard. For given boiler and condenser pressure as the

temperature increases the cycle efficiency increases and the specific steam consumption decreases as shown in fig. 3.3(b).

er Pressure: The average temperature during the heat addition process can be increased by

increasing the operating pressure of the boiler which automatically raises the temperature of boiling. This in turn raises the average temperature at which heat is added to the steam and increases the thermal efficiency.

The effect of increasing the boiler pressure on the performance of Rankine cycle is s diagram in Fig. 3.4(a) and steam cycle efficiency and specific steam

consumption against boiler pressure in fig. 3.4(b). As the boiler pressure increases the specific enthalpy of evaporation decreases thus less heat is added at the maximum cycle temperature Efficiency first increases with boiler pressure initially due to maximum cycle

ised but then decreases by lowering of the mean temperature at which heat is added. Therefore the graph of efficiency rises, reaches maximum and then falls.

The turbine inlet temperature is kept same in both cases and notice that for a fixed t temperature, the cycle shifts to the left and the moisture content of steam at

boiler exit increases. This undersirable effects can be corrected using reheating discussed in the next section.


The hatch area on the diagram represents the increase in the net work. The total area the curve 22 represents the increase in the heat input. Thus both the network and heat

of superheating the steam. The overall effect is an increase in thermal efficiency, since the average temperature at which heat is added increases. Superheating the steam has another desirable effect, that the moisture content of the steam at

s diagram (the quality at 3’ is higher than able since these water particles

The temperature to which steam can be superheated is limited by metallurgical considerations. Presently steam temperature allowed at turbine inlet is 620oC. Ceramics are very promising materials in this regard. For given boiler and condenser pressure as the

temperature increases the cycle efficiency increases and the specific steam

The average temperature during the heat addition process can be increased by increasing the operating pressure of the boiler which automatically raises the temperature of

dded to the steam and

the boiler pressure on the performance of Rankine cycle is s diagram in Fig. 3.4(a) and steam cycle efficiency and specific steam

ure in fig. 3.4(b). As the boiler pressure increases the specific enthalpy of evaporation decreases thus less heat is added at the maximum cycle temperature Efficiency first increases with boiler pressure initially due to maximum cycle

ised but then decreases by lowering of the mean temperature at which heat is added. Therefore the graph of efficiency rises, reaches maximum and then falls.

The turbine inlet temperature is kept same in both cases and notice that for a fixed t temperature, the cycle shifts to the left and the moisture content of steam at

boiler exit increases. This undersirable effects can be corrected using reheating method as

Operating pressures are gradually increasing and touse today. Today many modern steam power plants at supercritical pressure (p > 22.09 MPa) and have thermal efficiency of 40% for fossil

The moisture (M), thermal efficiency, cycle are plotted in Fig. 3.5 as a function of maximum temperature, and maximum and minimum pressure for the ideal cycle.

The maximum steam temperature is limited by superheater section of the steam generator and in the high pressure turbine. Most modern steam power plants are limited to maximum operating temperature of 540 to 600maximum steam pressure is limited by the operating coparticularly by the moisture contents at the turbine exhausts. The minimum in the condenser is limited by the temperature of the cooling water.

The thermal efficiency of the ideal Rankine cycle is stronglof the pump and turbine. These systems irreversible convert some the mechanical energy into thermal energy, thereby increasing the enthalpy of fluid leaving the components. In the steam turbine this


Operating pressures are gradually increasing and to pressures about 300 bar are in use today. Today many modern steam power plants at supercritical pressure (p > 22.09 MPa) and have thermal efficiency of 40% for fossil-fuel plants and 34% for nuclear plants.

The moisture (M), thermal efficiency, and specific work, w, of the basic Rankine cycle are plotted in Fig. 3.5 as a function of maximum temperature, and maximum and minimum pressure for the ideal cycle.

The maximum steam temperature is limited by the material employed in the superheater section of the steam generator and in the high pressure turbine. Most modern steam power plants are limited to maximum operating temperature of 540 to 600maximum steam pressure is limited by the operating conditions in the steam generator and particularly by the moisture contents at the turbine exhausts. The minimum in the condenser is limited by the temperature of the cooling water.

The thermal efficiency of the ideal Rankine cycle is strongly affected by efficiencies of the pump and turbine. These systems irreversible convert some the mechanical energy into thermal energy, thereby increasing the enthalpy of fluid leaving the components. In the


pressures about 300 bar are in use today. Today many modern steam power plants at supercritical pressure (p > 22.09

fuel plants and 34% for nuclear plants.

and specific work, w, of the basic Rankine cycle are plotted in Fig. 3.5 as a function of maximum temperature, and maximum and

the material employed in the superheater section of the steam generator and in the high pressure turbine. Most modern steam power plants are limited to maximum operating temperature of 540 to 600oC. The

nditions in the steam generator and particularly by the moisture contents at the turbine exhausts. The minimum vapour pressure

y affected by efficiencies of the pump and turbine. These systems irreversible convert some the mechanical energy into thermal energy, thereby increasing the enthalpy of fluid leaving the components. In the

effect is referred to as ‘stage reheat’ The lower turbine efficiency adverly effects the overall performance.

• The Reheat Rankine CycleThe advantage of increased efficiency at higher boiler pressure can be taken using

reheating method of steam at intermediate stage disadvantage of use of high pressure steam which increases the moisture content in the turbine. Reheating is a practical solution to the excessive moisture problem in turbines and is used frequently in modern steam power The schematic way and the reheat Rankine cycle on T The reheat Rankine cycle differs from the simple Rankine cycle in that the expansion process takes place in two stages. In the first stage (the high pressure turbsteam is expanded isentropic ally to an intermediate pressure and sent back to the where it is reheated at constant pressure and usually to the same inlet turbine. Steam then expands isentropic ally in the second stage (the low pressure turbine) to the condenser pressure. The reheat can be and passing it through a special bank of tube


erred to as ‘stage reheat’ The lower turbine efficiency adverly effects the

The Reheat Rankine Cycle: The advantage of increased efficiency at higher boiler pressure can be taken using

reheating method of steam at intermediate stage in the turbine. This overcomes the disadvantage of use of high pressure steam which increases the moisture content in the turbine. Reheating is a practical solution to the excessive moisture problem in turbines and is used frequently in modern steam power plants.

The schematic way and the reheat Rankine cycle on T-s diagram is shown in fig. 3.6

The reheat Rankine cycle differs from the simple Rankine cycle in that the expansion process takes place in two stages. In the first stage (the high pressure turb

isentropic ally to an intermediate pressure and sent back to the where it is reheated at constant pressure and usually to the same inlet temperature of the first turbine. Steam then expands isentropic ally in the second stage (the low pressure turbine) to the condenser pressure. The reheat can be carried out by returning the steam to the boiler,

a special bank of tubes, the reheat bank of tubes being situated in the


erred to as ‘stage reheat’ The lower turbine efficiency adverly effects the

The advantage of increased efficiency at higher boiler pressure can be taken using in the turbine. This overcomes the

disadvantage of use of high pressure steam which increases the moisture content in the turbine. Reheating is a practical solution to the excessive moisture problem in turbines and

s diagram is shown in fig. 3.6

The reheat Rankine cycle differs from the simple Rankine cycle in that the expansion process takes place in two stages. In the first stage (the high pressure turbine),

isentropic ally to an intermediate pressure and sent back to the boiler temperature of the first

turbine. Steam then expands isentropic ally in the second stage (the low pressure turbine) to carried out by returning the steam to the boiler, s, the reheat bank of tubes being situated in the

proximity of the super heater tubes. The use of of high pressure boilers, since the specific fuel consumption is improved and dryness fraction of the exhaust stea

Thus the total heat input and the total turbine work for reheat cycle becomes.

Qin

WTurbine

Cycle efficiency =

=

The cycle efficiency is not greatly affected by reheating. The efficiency of the Rankine cycle may increase or decrease somewhat as a result of reheating average temperature at which heat is added during reheating. The temperature should be maintained as high as possibledecreasing the cycle efficiency. Also care must be taken to prevL.P. turbine from falling into the superheated vapour region, since this will increase the rejection of more heat and thus the cycle efficiency to decreases.

The average temperature during reheat cycle can be increased by incrnumber of expansion and reheat stages, which will make the heat additiontemperature. The optimum number is determined by economical consideration. Remember that the sole purpose the reheat cycle is to reduce the moisture content of stage of the expansion.


proximity of the super heater tubes. The use of reheat cycle has encouraged the development of high pressure boilers, since the specific fuel consumption is improved and dryness fraction of the exhaust steam is increased.


in = Qprimary + Qreheat

= (h2 – h7) + (h4 + h3) kJ / kg

Turbine = WH.P.turbine + WL.P.turbine

= (h2 – h3) + (h4 + h5) kJ / kg

Cycle efficiency =

=

The cycle efficiency is not greatly affected by reheating. The efficiency of the Rankine cycle may increase or decrease somewhat as a result of reheating average temperature at which heat is added during reheating. The temperature should be maintained as high as possible without allowing excessive moisture to be formed and not decreasing the cycle efficiency. Also care must be taken to prevent the existing state of the L.P. turbine from falling into the superheated vapour region, since this will increase the rejection of more heat and thus the cycle efficiency to decreases.

average temperature during reheat cycle can be increased by incrnumber of expansion and reheat stages, which will make the heat additiontemperature. The optimum number is determined by economical consideration. Remember that the sole purpose the reheat cycle is to reduce the moisture content of


reheat cycle has encouraged the development of high pressure boilers, since the specific fuel consumption is improved and dryness


The cycle efficiency is not greatly affected by reheating. The efficiency of the Rankine cycle may increase or decrease somewhat as a result of reheating depending on the average temperature at which heat is added during reheating. The temperature should be

without allowing excessive moisture to be formed and not ent the existing state of the

L.P. turbine from falling into the superheated vapour region, since this will increase the

average temperature during reheat cycle can be increased by increasing the number of expansion and reheat stages, which will make the heat addition at constant temperature. The optimum number is determined by economical consideration. Remember that the sole purpose the reheat cycle is to reduce the moisture content of steam at the final

• Regenerative Rankine Cycle:The efficiency of Rankine cycle is less than Carnot cycle because in Rankine cycle

all the heat is not added at the higher temperature as in Carnot cycle. Heat added in the Rankine cycle is as shown in Fig. 3.7.

Fig. 3.7 reveals that heat is added to the steam during the process 5low temperature. This lowers the average temperature at which heat is added and thus the cycle efficiency.

To overcome this saturation temperature corresponding to boiler pressure, before it enters the boiler. This is achieved by what is known as regeneration. In regeneration the feed water is heated by transferring heat from expending steam in the turbine, in a counter flow heat exchanger built into the turbine itself as shown in fig. 3.8 The cycle in which this method is used to raise the efficiency is called a regeneration cycle. Fig. 3.9 shows the cycle on T

The feed water at 6 is passed into passage in the turbine casing at the point where the expanding steam has temperature only infinitemally greater than 6. The water flows in a direction opposite to that of expanding steam and is thereby heated to a temperature only infinitestimally smaller than 2 before it passes into the boiler. At all points the heat transferis effected by infinitesimal temperature difference and the process is therefore reversible.


Regenerative Rankine Cycle: The efficiency of Rankine cycle is less than Carnot cycle because in Rankine cycle

all the heat is not added at the higher temperature as in Carnot cycle. Heat added in the cycle is as shown in Fig. 3.7.

Fig. 3.7 reveals that heat is added to the steam during the process 5low temperature. This lowers the average temperature at which heat is added and thus the

To overcome this short coming, one methods is by raising the feed water to the saturation temperature corresponding to boiler pressure, before it enters the boiler. This is

known as regeneration. In regeneration the feed water is heated by heat from expending steam in the turbine, in a counter flow heat exchanger built

into the turbine itself as shown in fig. 3.8 The cycle in which this method is used to raise the efficiency is called a regeneration cycle. Fig. 3.9 shows the cycle on T-s dia

The feed water at 6 is passed into passage in the turbine casing at the point where the temperature only infinitemally greater than 6. The water flows in a

direction opposite to that of expanding steam and is thereby heated to a temperature only infinitestimally smaller than 2 before it passes into the boiler. At all points the heat transferis effected by infinitesimal temperature difference and the process is therefore reversible.


The efficiency of Rankine cycle is less than Carnot cycle because in Rankine cycle all the heat is not added at the higher temperature as in Carnot cycle. Heat added in the

Fig. 3.7 reveals that heat is added to the steam during the process 5-1 at a relatively low temperature. This lowers the average temperature at which heat is added and thus the

short coming, one methods is by raising the feed water to the saturation temperature corresponding to boiler pressure, before it enters the boiler. This is

known as regeneration. In regeneration the feed water is heated by heat from expending steam in the turbine, in a counter flow heat exchanger built

into the turbine itself as shown in fig. 3.8 The cycle in which this method is used to raise the s diagram.

The feed water at 6 is passed into passage in the turbine casing at the point where the temperature only infinitemally greater than 6. The water flows in a

direction opposite to that of expanding steam and is thereby heated to a temperature only infinitestimally smaller than 2 before it passes into the boiler. At all points the heat transfer is effected by infinitesimal temperature difference and the process is therefore reversible.

Most of the expansion in the turbine is no longer an adiabatic process and it follows the path 2-3-4 Since the heat rejected in process 2shaded areas on T-s diagram in fig. 7.9 must be equal. The heat supplied frosource is equal to the area under process 1area under the process 4-regenerative cycle and the Carnot cycle 1278 are equaexternally is done at constant temperature. On the other hand the work ratio of the regenerative cycle, requiring the negligible pump work = (hthat of the Carnot cycle and is comparab

Such a regenerative cycle is impractical for two reasons. Firstly it would be impossible to design a turbine which would operate efficiently as both turbine and heat exchanger. Secondly the steam expanding through the turbfraction.

Thus this method is not a practical but is of academic interest. However the Ranking efficiency can be improved upon in practice by bleeding off some steam for feed water heating.


Most of the expansion in the turbine is no longer an adiabatic process and it follows 4 Since the heat rejected in process 2-3 equals that supplied

s diagram in fig. 7.9 must be equal. The heat supplied frosource is equal to the area under process 1-2, and heat rejected to external sink equals the

-5. Inspection of the area involved shows that the efficiencies of the regenerative cycle and the Carnot cycle 1278 are equal. Since the heat supplied and rejected externally is done at constant temperature. On the other hand the work ratio of the regenerative cycle, requiring the negligible pump work = (h6 = h5) is very much higher than that of the Carnot cycle and is comparable to that of the Rankine cycle.

Such a regenerative cycle is impractical for two reasons. Firstly it would be impossible to design a turbine which would operate efficiently as both turbine and heat exchanger. Secondly the steam expanding through the turbine would have very low dryness

Thus this method is not a practical but is of academic interest. However the Ranking efficiency can be improved upon in practice by bleeding off some steam for feed water


Most of the expansion in the turbine is no longer an adiabatic process and it follows 3 equals that supplied in process 6.1 and

s diagram in fig. 7.9 must be equal. The heat supplied from the external 2, and heat rejected to external sink equals the

5. Inspection of the area involved shows that the efficiencies of the l. Since the heat supplied and rejected

externally is done at constant temperature. On the other hand the work ratio of the ) is very much higher than

Such a regenerative cycle is impractical for two reasons. Firstly it would be impossible to design a turbine which would operate efficiently as both turbine and heat

ine would have very low dryness

Thus this method is not a practical but is of academic interest. However the Ranking efficiency can be improved upon in practice by bleeding off some steam for feed water


Page | 44

• Fuels And Combustion • Introduction

Until the invention of atomic energy, the simplest way to obtain the energy was burning the combustible substances, such as wood, coal bagasse etc. All these substances which are used as the sources of energy are known as fuels.

Fuel Definition: Fuel is a substance mainly composed of Carbon and Hydrogen, which can undergo a chemical reaction with Oxygen under suitable conditions. This chemical reaction is known as combustion. It is basically an Oxidation process, its nature is exothermic, so it is associated with the release of heat energy. Thus at the end of combustion process, we get oxides as CO, CO2, H2 O, SO2, etc. along with Nitrogen supplied with the air, which are known as products of combustion.

• Classification Fuels are broadly classified as,

1. Solid fuels 2. Liquid fuels 3. Gaseous fuels

1. Solid fuels: Solid fuels may be a) Natural solid fuels b) Artificial or prepared solid fuels

a) Natural solid fuels: The fuels belonging to this group are, i) Wood: It is not considered as commercial fuel. It largely consists of carbon

and hydrogen chemically formed by the action of sunlight and was as one time extensively used as a fuel. It’s calorific value varies with the kind of wood and its water content.

ii) Peat: It represents the first stage at which fuel is derived. It contains 20 to 30% of water. The calorific value of air dried peat is about 14,500 kJ/Kg.

iii) Lignite: It is very soft and an inferior type of coal containing not less than 60% Carbon. It is largely used as low grade fuel. The average heating value of coal after drying in air is 21,000 KJ/Kg and burns with a large smoky

iv) Bituminous coal: It is the next intermediate stage in the development; it is soft and shiny, black in appearance and contains about 70% Carbon. It’s average C.V. is about 31,500 KJ/Kg. It burns with a long yellow and smoky flame Bituminous coal be classified as non caking and caking.

v) Anthracite: It is the final stage in the development. It is hard, brittle and consists of about 90% Carbon and 8 to 10% volatile matter.

b) Artificial or prepared solid fuels: The fuels belonging to this group are: i) Wood charcoal ii) Coke iii) Briquetted coal iv) Pulverised coal

2. Liquid fuels:

Carbon and Hydrogen. Most of the liquid fuels are obtained from Petroleum. Petroleum is a mixture of many different hydrocarbons. These general categories, P Liquid fuels are commnly used in I.C. Engine and other power plants. The merits and demerits of these fuels are as follows.Merits:

i) It has a high calorific valueii) It is easy to store and it occupies less space.iii) Easy to control and handleiv) System is neat and clan in appearance.v) Elimination of were and tear of grate bars in steam power plants.vi) Ease of ignition and shutting off the operationvii) Changes in load in power plant can be easily met.viii) Combustion losses are low.

Demerits: As compared to the solid or gaseous fuels, liquid fuels are more costly.

3. Gaseous fuels:

a) Natural gas.b) Artificial gas.

a) Natural Gas:

calorific value varies from 35,00 KJ/Kg to 37,200 KJ/Kgb) Artificial gas:

Liquefied Petroleum Gas:

considerable amount of Propane and Butane gas is produced. Propane gas liquids at 8.8 bar and Butane gas at 2.1 barcylinder and these are used for domestic and industrial application.


Liquid fuels: In all the liquid fuels, the basis combustible elements are Carbon and Hydrogen. Most of the liquid fuels are obtained from Petroleum. Petroleum is a mixture of many different hydrocarbons. These hydrocarbons are grouped into four general categories, Paraffins, Oleffine, Naphthenes, Aromatics.

Liquid fuels are commnly used in I.C. Engine and other power plants. The merits and demerits of these fuels are as follows.

It has a high calorific value It is easy to store and it occupies less space. Easy to control and handle System is neat and clan in appearance. Elimination of were and tear of grate bars in steam power plants.Ease of ignition and shutting off the operation Changes in load in power plant can be easily met. Combustion losses are low.

As compared to the solid or gaseous fuels, liquid fuels are more costly.

Gaseous fuels: These fuels may be divided into two classes:Natural gas. Artificial gas.

Natural Gas: It mainly consists of Methane, Ethylene, Ocalorific value varies from 35,00 KJ/Kg to 37,200 KJ/Kg Artificial gas:

Liquefied Petroleum Gas: During the refining process of petroleum, considerable amount of Propane and Butane gas is produced. Propane gas liquids at 8.8 bar and Butane gas at 2.1 bar and temp. of 21.1oC. These liquefied gases can be stored in steel cylinder and these are used for domestic and industrial application.


In all the liquid fuels, the basis combustible elements are Carbon and Hydrogen. Most of the liquid fuels are obtained from Petroleum. Petroleum

hydrocarbons are grouped into four

Liquid fuels are commnly used in I.C. Engine and other power plants.

Elimination of were and tear of grate bars in steam power plants.

As compared to the solid or gaseous fuels, liquid fuels are more costly.

These fuels may be divided into two classes:

It mainly consists of Methane, Ethylene, O2, CO3 and CO2. Its

During the refining process of petroleum, considerable amount of Propane and Butane gas is produced. Propane gas liquids at 8.8 bar

C. These liquefied gases can be stored in steel


Page | 46

ii) producer Gas: It consists of products derived from the passage of air and steam through a bed of incandescent fuel in gas producers. This gas is a mixture of CO, CO2, Hydrogen and Nitrogen. The Essential component of producer gas is Carbon Monoxide. Its’ calorific value from 4200 to 6600 kJ/m3.

iii) Blast furnace gas: It is obtained as a bi product in the smelting of pig iron. It has a low heating value of 3800 kJ/m3. This gas is a mixture of CO, CO2 Hydrogen, Nitrogen and some traces of Methane. This gas contains considerable amount of dust and must be cleaned before it is used.

iv) Marsh gas: It is a simple hydrocarbon gas produced in nature by decay of vegetable matter under water. It’s calorific value is about 23,000 kJ/m3. • Laws of Combustion

1. Low of conservation of mass: It states that the matter can neither be create nor be destroyed. Through in combustion process the atoms of reactants rearrange themselves after the combustion with the liberation of chemical energy, but the total mass of the material during the combustion process remains constant

C + O2 = CO2

This equation indicates that one weight atom of Carbon of molecular weight. 12 and two atoms of Oxygen of molecular weight 32 combine in a combustion process which must produce a mole of CO2 of molecular weight 44 according to the law.

2. Law of conservation of energy: It states that energy can neither be created nor be destroyed, which is the basis of first law of thermodynamics.

3. Law of combining weights: It states that the substances combining during the

chemical reaction in accordance with some definite weight relationship. These weight rations are the exact rations of molecular weight of the constituents entering the combustion reaction.

4. Ideal gas laws: All combustion equations follow the ideal gas equations defined by Boyle’s law, Charles law general gas law.

PV = mRT.

5. Avogadro’s law: It states that all the perfect gases occupy the same volume under the similar conditions of pressure and temperature.

6. Dalton’s law of pressures: It states that the total pressure of the mixture of perfect gases is the sum of partial pressure which would be exerted by each of the constituent if each gas were to occupy alone the same volume as of the mixture at the same temp.

(P)VT = (P1)VT + (P2)VT + (P3)VT

7. Amagat’s law: It states that the total volume occupied by the mixture of gases is

equal to the sum of volumes which could be occupied by each of the constituent when they are at the same pressure and temperature as that of the mixture. (V)P1 T = (V1)P1 T + (V2)P1 T + (V3)P1 T.


Page | 47

• Coal Analysis Coal as found in nature is neither a pure substance nor of uniform composition.

A definite chemical formula cannot therefore be written for a coal found in coal mines. Consequently two different methods of analysis are employed to know the composition of coal. They are known as Ultimate analysis and Proximate analysis. In Ultimate Analysis a complete chemical breakdown of coal into its chemical constituents is carried out by chemical process. This analysis is required when important large scale trials are being performed. The analysis serves the basis for calculation of the amount of air required for complete combustion of the kg of fuel. The analysis gives the % content on mass basis of carbon, H2, N2, O2, S, and ash, and their sum is taken as equal to 100%. Moisture is expressed as a separate item. The analysis also enable us to determine C.V. or heating value of coal.

Proximate analysis is the separation of coal into its physical components and can be made without the knowledge of analytical chemistry. The analysis is made by means of a chemical balance and a temperature controlled furnace. The sample of fuel is heated in the furnace or oven. The component in the analysis are fixed carbon, volatile matter, moisture and ash. These components are expressed in % on mass basis and their sum is taken as 100%. Sulphur is determined separately. This analysis also enables us to determine the heating value of coal.

• Calorific Value of Fuels It is the amount of heat energy liberated, when one kg of fuel is burnt.

For solid or Liquid fuels, the Calorific Value (C.V.) is expressed in kJ/kg and for Gaseous fuels in kJ/m3 of gas. All the hydrocarbon fuels will produce water vapour during combustion. So some part of heat liberated is utilized for the evaporation and thus the remaining part of heat will be available. The total amount of heat liberated in the combustion is known as Higher or Gross Calorific Value ( H.C.V.) The Lower Calorific Value (L.C.V.) of the fuel, is the heat liberated per kg or per cubic meter of fuel, after the enthalpy necessary to vaporise the steam formed by the combustion of hydrogen in the fuel is deducted. L.C.V. = H.C.V. – Heat carried by water vapour formed per kg of fuel burnt. = H.C.V – Enthalpy of evaporation of steam formed. It is common practice to assume that the evaporation takes place at saturation temperature of 100oC. The enthalpy of evaporation of steam at 1.01325 bar (i.e. 1 atmosphere pressure) is 2257 kJ/kg. Also 1 kg of Hydrogen combines with Oxygen to form 9 kg of steam. So, amount of water vapour formed during combustion of 1 kg of fuel will be 9 H2. � L.C.V. = H.C.V. – 9 H2 � 2257 kJ/kg = H.C.V. – mw � 2257 kJ/kg

where mw = mass of water vapour formed per kg of fuel burnt. The Calorific value of fuel may be found theoretically by using Dulong’s

formula and experimentally by a fuel Calorimeter.

• Theoretical Calorific ValueThe theoretical calorific value of a fue

the ultimate analysis of fuel is available and if the calorific value of the elementary combustibles (carbon, hydrogen and sulphur) are known, then the calorific value of the fuel is approximately the sum o

Formula: Theoretical C.V. of fuel

= 33800

Here the symbols C, HHydrogen Oxygen and Sulphur in Kg/Kg of fuel and the numericals indicate their

indicate their respective calorific values in kJ/Kg. The expression

available H2 for heat release, i.e. the amount left after subtracting the amount of Hydrogen

that will unite with Hydrogen present in the left to form water Mass of H

the mass of O2.

• The Experimental Determination of Calorific Value of FuelsThe determination of C.V. of fuel is carried out in specially designed calorimeters.

The type of calorimeter used and some liquid fuels the Calorific value is usually determined by Bomb In case of gaseous and some liquid fuels the Calorific Value is determined in a Gas Calorimeter.

a) Bomb Calorimeter:heat liberated due to the combustion is transferred to a definite matemperature rise is measured. The Calorimeter consist of a thick walled, stainless steel high pressure


Theoretical Calorific Value The theoretical calorific value of a fuel may be calculated by using Dulong’s formula. If

ltimate analysis of fuel is available and if the calorific value of the elementary combustibles (carbon, hydrogen and sulphur) are known, then the calorific value of the fuel is approximately the sum of the heat liberated by these combustibles.

Theoretical C.V. of fuel

= 33800 C + 144500

Here the symbols C, H2, O2 and S represent the mass of Carbone, Hydrogen Oxygen and Sulphur in Kg/Kg of fuel and the numericals indicate their

indicate their respective calorific values in kJ/Kg. The expression

for heat release, i.e. the amount left after subtracting the amount of Hydrogen

will unite with Hydrogen present in the left to form water Mass of H

The Experimental Determination of Calorific Value of Fuels determination of C.V. of fuel is carried out in specially designed calorimeters.

The type of calorimeter used will depend upon the type of fuel used. In case of solid fuels and some liquid fuels the Calorific value is usually determined by Bomb

In case of gaseous and some liquid fuels the Calorific Value is determined in a Gas

Bomb Calorimeter: In this Calorimeter a known quantity of fuel is burnt and heat liberated due to the combustion is transferred to a definite mass of temperature rise is measured.

The Calorimeter consist of a thick walled, stainless steel high pressure


l may be calculated by using Dulong’s formula. If ltimate analysis of fuel is available and if the calorific value of the elementary

combustibles (carbon, hydrogen and sulphur) are known, then the calorific value of the fuel

Hydrogen Oxygen and Sulphur in Kg/Kg of fuel and the numericals indicate their

represents the

for heat release, i.e. the amount left after subtracting the amount of Hydrogen

will unite with Hydrogen present in the left to form water Mass of H2 in water is of

determination of C.V. of fuel is carried out in specially designed calorimeters. In case of solid fuels

and some liquid fuels the Calorific value is usually determined by Bomb Calorimeter. In case of gaseous and some liquid fuels the Calorific Value is determined in a Gas

In this Calorimeter a known quantity of fuel is burnt and ss of water and the

The Calorimeter consist of a thick walled, stainless steel high pressure

cylinder, called Bomb, hence the name Bomb Calorimeter. On the top of Bomb a non return O2 supply value, and a pressure release valve are fitted. The Calorimeter is fitted with stirring device and a Beck mann

Before the start of the experiment, the crucible is weighted. A pillet is

formed in Briquette moulding apparatus (as shown in fig. 13.3) of the given sample of fuel. The weight of the pillet is also noted. The pillet is placed in the crucible made of silica of quartz. A known quantity of water is taken in the calorimeter. The OBomb, so that the pressure inside the Bomb is approximately 25 bar. The initial temperature of water is noted and then the Calorimeter is stirred continuously.

The temperature rise of the water is noted at regular intervals of time. The temperature of water increases as the heat released by the combustion of fuel in transferred to the water and the Calorimeter.

When the temperature rise of the water is noted at regular intemperature of water increases as the heat released by the combustion of fuel in transferred to the water and the Calorimeter.

When the temperature of water reaches to its maximum value, it is observed that the temperature starts falling due to heat transfer losses to the

By noting this decrease in temperature at a fixed interval of time, the rate of cooling can be obtained. This rate of cooling helps in applying a cooling correction factor. Theis is necessary in order to determine the actual rise in temperature of water of Calorimeter.


cylinder, called Bomb, hence the name Bomb Calorimeter. On the top of Bomb a non return supply value, and a pressure release valve are fitted. The Calorimeter is fitted with

stirring device and a Beck mann thermometer as shown in fig. 13.2.


formed in Briquette moulding apparatus (as shown in fig. 13.3) of the given sample of fuel. The weight of the pillet is also noted. The pillet is placed in the crucible made of silica of

quantity of water is taken in the calorimeter. The OBomb, so that the pressure inside the Bomb is approximately 25 bar. The initial temperature of water is noted and then the fuel is ignited with the help of fuse wire and the water in the Calorimeter is stirred continuously.

ature rise of the water is noted at regular intervals of time. The temperature of water increases as the heat released by the combustion of fuel in transferred to the water and the Calorimeter.

When the temperature rise of the water is noted at regular intervals of time. The temperature of water increases as the heat released by the combustion of fuel in transferred to the water and the Calorimeter.

When the temperature of water reaches to its maximum value, it is observed that the ing due to heat transfer losses to the oundings.

By noting this decrease in temperature at a fixed interval of time, the rate of cooling can be obtained. This rate of cooling helps in applying a cooling correction factor. Theis is

termine the actual rise in temperature of water of Calorimeter.


cylinder, called Bomb, hence the name Bomb Calorimeter. On the top of Bomb a non return supply value, and a pressure release valve are fitted. The Calorimeter is fitted with


formed in Briquette moulding apparatus (as shown in fig. 13.3) of the given sample of fuel. The weight of the pillet is also noted. The pillet is placed in the crucible made of silica of

quantity of water is taken in the calorimeter. The O2 is supplied to the Bomb, so that the pressure inside the Bomb is approximately 25 bar. The initial temperature

fuel is ignited with the help of fuse wire and the water in the

ature rise of the water is noted at regular intervals of time. The temperature of water increases as the heat released by the combustion of fuel in transferred

tervals of time. The temperature of water increases as the heat released by the combustion of fuel in transferred

When the temperature of water reaches to its maximum value, it is observed that the

By noting this decrease in temperature at a fixed interval of time, the rate of cooling can be obtained. This rate of cooling helps in applying a cooling correction factor. Theis is

termine the actual rise in temperature of water of Calorimeter.


Page | 50

Calculations:

Let,

mf = Mass of fuel burnt in kg.

C.V.= Calorific Value of fuel.

me = Mass of calorimeter.

mw = Mass of water in the Calorimeter.

Cc = Specific heat of Calorimeter.

Cpw = Specific heat of water 4.19 kJ/kg.k.

∆ T = Rise in temperature.

The product (mc . Cc) is called the Water equivalent of the Calorimeter.

Then,

Heat energy released due to Combustion of fuel = Heat energy absorbed by (water and Calorimeter)

mf � C.V. = mw . Cpw . ∆ T + mc. Cpc� ∆ T

From this equation, the calorific value C.V. can be found.

b) Boy’s gas calorimeter: Boy’s gas calorimeter is used for the determination of calorific value of gaseous fuels. The main parts of the calorimeter are burner,, chimney and the cooling coils, as shown in fig. 13.4. The gas is supplied whose calorific value is to be determined. A gas meter is attached to measure the rate of volume of gas supplied. The fuel gas is burned and the products of combustion rise in the chimney as shown by the arrows. The heat liberated due to combustion of fuel is transferred to cooling water. The water first enters the outer cooling coils and then it returns upwards through coils as shown in figure. The water vapour formed gets condensed in the outer portion of the chimney and the condensed is collected and weighted. Three thermometers are provided to measure the temperature of cooling water at inlet and outlet and also to measure the temperature of products of combustion at exit. It is ensured that these flue gases are coiled upto atmospheric temperature. Calculations: Vg = Volume of gas supplied. Pg = Pressure of gas supplied. Tg = Temperature of gas supplied. mw = Mass of water circulated. t1 = Temperature of cooling water at inlet. t2 = Temperature of cooling water at outlet. C.V. = Calorific value of gaseous fuel in kJ/m3 CPW = Specific heat of water = 4.19 kJ/kg K. V = Volume of gas supplied at S.T.P.


Page | 51

��

��

��

�

P = 1.013 bar T = Standard temperature = 25oC or 298 K

� V = Pg Vg . �

�� …. (1)

By energy balance, heat given by fuel = Heat absorbed by cooling water. V � C. V. = mw � Cpw (t2 – t1) …. (2)

� C.V. = ��.��

�

From (1) and (2)

C.V. = ��.��

��.��.�

��

…. (3)

From the above equation C.V. of gas can be calculated.

• Flue Gas Analysis Orsat’s apparatus is used for the analysis of dry flue gas by volume.

It consists of there reagent pipettes to absorb CO2 and O2, CO by their respective absorbants kept in the flask are NaOH or KOH, alkaline solution of Pyrogalic acid and the acidic solution of Cuprous chloride. The aspirating bottle is used at develop a hydrostatic head to force the flue gas from the measuring bottle to the reagent pipettes and back.

The following of the apparatus is follows:

A sample of flue gas is drawn in the measuring bottle by lowering the level of aspirating bottle. The flue gas in excess of 100 cc is expelled to the atmosphere via the three way cock. The CO2 component is absorbed by the solution of KOH and the aspirating bottle is lowered to its original position. The difference is level (before and after absorbing CO2) gives the percentage of CO2 by volume in the flue gases. However to ensure that CO2 is fully absorbed the process is repeated several time.

Now the cock ‘a’ is closed. The procedure is repeated with the flasks ‘B’ and ‘C’ to find the percentage analysis of O2 and CO respectively in the flue gases.

When the percentages of CO2, O2 and CO is determined, the remainder of the gas sample is assumed to be Nitrogen N2.

It should be noted that Orsat apparatus gives the analysis of dry flue gases since the water vapour is condensed at atmospheric conditions. In order to get proper results for the analysis of flue gases, the above.

• Air Compressor• Introduction

In many industrial purposes high pressure gases or air are required. A machine providing gas at high pressure is called a compressor gas by an external agency. An air compressor takes in air at atmospheric pressure, compresses it at the cost of the work supplied, and delivers the high pressure air to a storage vessel called receiver from which it may be conveyed by the pipe line to a place where the supply of compressed air is required.

The uses of compressed air are vast in (1) Cleaning work(2) Starting I.C. engines.(3) Spraying fuel in high speed diesel engines.(4) Spraying paints in paint industries.(5) Construction of bridges, roads, dam, structural work, sewage and tunnels. (6) Cooling large buildings.(7) Operation of pneumatic drills, wrenches, air motors, hummers, also for rivetting

and tightening nuts etc.(8) Supercharging I.C. engines and in working of gas turbi

• Classification Of Air CompressorsThe compressors are broadly (i) Reciprocating compressors(ii) Rotary compressors


It should be noted that Orsat apparatus gives the analysis of dry flue gases since the condensed at atmospheric conditions. In order to get proper results for the

flue gases, the absorption of gases must occurs in the same sequence as indicated

Air Compressor

In many industrial purposes high pressure gases or air are required. A machine providing gas at high pressure is called a compressor and work must be done upon the gas by an external agency. An air compressor takes in air at atmospheric pressure,

s it at the cost of the work supplied, and delivers the high pressure air to a storage vessel called receiver from which it may be conveyed by the pipe line to a place where the supply of compressed air is required.

The uses of compressed air are vast in industries some of them are for Cleaning work-shops and automobiles. Starting I.C. engines. Spraying fuel in high speed diesel engines. Spraying paints in paint industries. Construction of bridges, roads, dam, structural work, sewage and tunnels.

large buildings. Operation of pneumatic drills, wrenches, air motors, hummers, also for rivetting and tightening nuts etc. Supercharging I.C. engines and in working of gas turbine plans.

Classification Of Air Compressors The compressors are broadly classified in two classes:

Reciprocating compressors Rotary compressors


It should be noted that Orsat apparatus gives the analysis of dry flue gases since the condensed at atmospheric conditions. In order to get proper results for the

of gases must occurs in the same sequence as indicated

In many industrial purposes high pressure gases or air are required. A machine and work must be done upon the

gas by an external agency. An air compressor takes in air at atmospheric pressure, s it at the cost of the work supplied, and delivers the high pressure air to a

storage vessel called receiver from which it may be conveyed by the pipe line to a place

industries some of them are for

Construction of bridges, roads, dam, structural work, sewage and tunnels.

Operation of pneumatic drills, wrenches, air motors, hummers, also for rivetting

ne plans.

Reciprocating air compressors, compresses air in a cylinder by reciprocating motion of piston and supplies high pressure air with intermittent discharge. Rotary compressors has compressed air at low pressure but with continuous and high discharge. Reciprocating air compressors may be single acting or double acting. And may be single stage or multistage. in multi stage compressor the air is compressed in number of stages.

• Single Stage Air CompressorThe principal parts of reciprocating air compressor are same as that for

shows a simplified section

acting air compressor. Crank is coupled to the delivery valves are automatic in their operation. They are open and closed by pressure difference on both the sides of valves and a spring is provided to closed valve in case pressure is equal on both the sides. In delivery stroke. During suction stroke piston moves downward due to which pressure in cylinder falls down below atmospheric and intake valve opens with atmospheric air is taken in during whole the stroke.

In delivery stroke piston moves inward and delivery valve are closed and compression proceeds; as the end of compression stroke the pressure increases above the receiver pressure. The high pressure air ovspring force on delivery valve; valve opens and air is discharged to the receiver. Thereceiver is a vessel act as a storage tank.


Reciprocating air compressors, compresses air in a cylinder by reciprocating motion of piston and supplies high pressure air with intermittent discharge.

Rotary compressors has rotating elements to compress air which supplies ressed air at low pressure but with continuous and high discharge.

air compressors may be single acting or double acting. And may be single stage or multistage. In single stage air is compressed in a stage and delivered whereas in multi stage compressor the air is compressed in number of stages.

Single Stage Air Compressor The principal parts of reciprocating air compressor are same as that for

shows a simplified section of a single stage single

acting air compressor. Crank is coupled to the prime mover or electric motor. Inlet and delivery valves are automatic in their operation. They are open and closed by pressure difference on both the sides of valves and a spring is provided to closed valve in case pressure is equal on both the sides. In working there are two stroke, suction stroke and delivery stroke. During suction stroke piston moves downward due to which pressure in cylinder falls down below atmospheric and intake valve opens with atmospheric air is taken in during whole the stroke.

stroke piston moves inward with compression of air in cylinder. Both the inlet and delivery valve are closed and compression proceeds; as the end of compression stroke the pressure increases above the receiver pressure. The high pressure air ov

on delivery valve; valve opens and air is discharged to the receiver. Theis a vessel act as a storage tank.


Reciprocating air compressors, compresses air in a cylinder by reciprocating motion

rotating elements to compress air which supplies

air compressors may be single acting or double acting. And may be compressed in a stage and delivered whereas

The principal parts of reciprocating air compressor are same as that for engine. Fig. 1

prime mover or electric motor. Inlet and delivery valves are automatic in their operation. They are open and closed by pressure difference on both the sides of valves and a spring is provided to closed valve in case

working there are two stroke, suction stroke and delivery stroke. During suction stroke piston moves downward due to which pressure in cylinder falls down below atmospheric and intake valve opens with atmospheric air is taken

with compression of air in cylinder. Both the inlet and delivery valve are closed and compression proceeds; as the end of compression stroke the pressure increases above the receiver pressure. The high pressure air overcomes the

on delivery valve; valve opens and air is discharged to the receiver. The

Working of air compressor mshown in Fig. 2. The indicatorprocess 4 - 1 is suction stroke during which air is drawn into cylinderP1. At the

end of suction stroke both suction and delivery valve are closed and air is then compressed by inward movement of piston. Process is represented by curve 1 pressure and reductio in volume. At point the receiver. At this point constant pressure along line 2 repeated. The net work required for compression and delivery of airby the area 1 – 2 – 3 – 4.

The amount of work done on the air depends upon the nature of compression curve; means whether it is isentropic or isothermal compression. However in actual practice. Compression will be between isentro

Refer the P – V diagram (Fig. 3) compression 1 and 1 – 2’’ is isothermal.


Working of air compressor may be represented on indicator diagram (Pshown in Fig. 2. The indicator diagram is drawn for compressor neglecting

1 is suction stroke during which air is drawn into cylinder at constant pressure

both suction and delivery valve are closed and air is then compressed inward movement of piston. Process is represented by curve 1 – 2, follows increase in

pressure and reductio in volume. At point 2, pressure is slightly greater than the pressure in e receiver. At this point discharge valve opens and delivery of compressed air take place at

constant pressure along line 2 – 3. Again suction stroke starts and cycle of operations will be repeated. The net work required for compression and delivery of air per cycle is represented

The amount of work done on the air depends upon the nature of compression curve; means whether it is isentropic or isothermal compression. However in actual practice. Compression will be between isentropic and isothermal.

V diagram (Fig. 3) compression 1 – 2’ is isentropic 1


ay be represented on indicator diagram (P-V diagram) drawn for compressor neglecting clearance. The

at constant pressure

both suction and delivery valve are closed and air is then compressed 2, follows increase in

2, pressure is slightly greater than the pressure in delivery of compressed air take place at

3. Again suction stroke starts and cycle of operations will be per cycle is represented

The amount of work done on the air depends upon the nature of compression curve; means whether it is isentropic or isothermal compression. However in actual practice.

2’ is isentropic 1 – 2 is polytropic

The curve representing isentropic compression is steeper then isothermal compression. The isentropic work required to be done on the air is represented by area 4 – 2’ 3. If the compression is isothermal work done is represented by area 4 Area 4 – 1 – 2’ – 3 is greater than area 4 out isothermal compression (n = 1) is less hence isothermal compression is economical and efficient. While compression if work to be supplied. Thus it will be seen that the work required for compression per cycle decreases as the value of n decreases.

Case – I: Now refer P compressor neglecting cleara

Let P1 = Intake pressure in N/m

P2 = Delivery pressure in N/m

Work done on air per cycle

W = Area under curve 4

= Area 0

- Area 0 -

• Multi Stage CompressionIn practice it is not possible to achieve isothermal compression reason being speed of

the compressor should be extremely slow therefore attempts are made to obtain approximately isothermal compression while compressor runs at high speed, method can be spraying cold water


The curve representing isentropic compression is steeper then isothermal compression. The isentropic work required to be done on the air is represented by area 4

2’ 3. If the compression is isothermal work done is represented by area 4 3 is greater than area 4 – 1 – 2” – 3. Therefore work done required to carry

out isothermal compression (n = 1) is less hence isothermal compression is economical and sion if found to be isentropic (n = 1.4); require more amount of

work to be supplied. Thus it will be seen that the work required for compression per cycle decreases as the value of n decreases.

Now refer P – V diagram 4 – 1 – 2 – 3 (PVn = C) for single stage compressor neglecting clearance (Fig. 3).

= Intake pressure in N/m2 or Pa

= Delivery pressure in N/m2 or Pa

Work done on air per cycle

W = Area under curve 4 – 1 – 2 – 3

= Area 0 – a – 2 – 3 + Area a – b – 1 – 2

Area 0 – b – 1 – 4

Multi Stage Compression In practice it is not possible to achieve isothermal compression reason being speed of

the compressor should be extremely slow therefore attempts are made to obtain approximately isothermal compression while compressor runs at high speed, method can

aying cold water into the cylinder during compression or provide jackets around


The curve representing isentropic compression is steeper then isothermal compression. The isentropic work required to be done on the air is represented by area 4 – 1

2’ 3. If the compression is isothermal work done is represented by area 4 – 1 – 2” – 3. Therefore work done required to carry

out isothermal compression (n = 1) is less hence isothermal compression is economical and equire more amount of

work to be supplied. Thus it will be seen that the work required for compression per cycle

= C) for single stage

In practice it is not possible to achieve isothermal compression reason being speed of the compressor should be extremely slow therefore attempts are made to obtain approximately isothermal compression while compressor runs at high speed, method can

the cylinder during compression or provide jackets around

cylinder and circulate cold water through it or adopting multi stage compression with inter cooling. In multi stage compression air is compressed in two separate cylinders. Pressure of air is increased in each stage and an intercooler is provided in between two stages to cool the compressed air to atmospheric (intake) temperature before entering to the next stage.

• Two Stage Air Compressor

A tow stage air compressor with intercooler is shown in Fig. 5(a).

Air is sucked at atmospheric pressure in L.P. cylinder at PThen it is compressed polytropic ally


cylinder and circulate cold water through it or adopting multi stage compression with inter cooling. In multi stage compression air is compressed in two

ate cylinders. Pressure of air is increased in each stage and an intercooler is provided in between two stages to cool the compressed air to atmospheric (intake) temperature before entering to the next stage.

Two Stage Air Compressor A tow stage air compressor with intercooler is shown in Fig. 5(a).

Air is sucked at atmospheric pressure in L.P. cylinder at P1 during suction stroke. polytropic ally along 1 – 2. From


cylinder and circulate cold water through it or adopting multi stage compression with inter cooling. In multi stage compression air is compressed in two or more stages in

ate cylinders. Pressure of air is increased in each stage and an intercooler is provided in between two stages to cool the compressed air to atmospheric (intake)

A tow stage air compressor with intercooler is shown in Fig. 5(a).

during suction stroke.

conditions 2’ it is delivered to water at constant pressure Pperfect cooling volume of air reduces from 2’ H.P. cylinder along line P3 to pressure P3 and then delivered to receiver at constant pressure P

When both the indicator diagram 5(a) and (b) are diagram as in Fig. 6. Diagram 1 Diagram for L.P. stage 1 the shaded area 2 – 2’ –intercooling. When cooling is perfect, Point 2 will lie on isothermal curve (Tshown.

• Advantages of Multistage CompressionThe main advantages of multistage (1) Volumetric efficiency increases as

cylinder clearance space.(2) As compression

compressor reduces.(3) Better mechanical balance and (4) Maximum temperature in the cycle is reduced thus less difficulty in lubrication.(5) Reduced leakage loss owing to reduced pressure difference on

piston and valves.(6) Reduced weight of cylinders.

• Factors Which Affects (Reduces) Volumetric Efficiency


conditions 2’ it is delivered to an intercooler where heat from the air is water at constant pressure P2. If air is cooled to intake temperature of L.P. it is called as perfect cooling volume of air reduces from 2’ – P2 of P2 – 2. This cooled air is admitted in to H.P. cylinder along line P2 – 2. In H.P. stage it is compressed polytropic ally along

and then delivered to receiver at constant pressure P3.

When both the indicator diagram 5(a) and (b) are overlapped we will get combined diagram as in Fig. 6. Diagram 1 – 3’ – P3 – P1 is single stage compression with law PVDiagram for L.P. stage 1 – 2’ – P2 – P1. For H.P. stage diagram is 2 – 3

– 3’ – 3 is saving in work with two stage compressor with perfect intercooling. When cooling is perfect, Point 2 will lie on isothermal curve (T

Advantages of Multistage Compression The main advantages of multistage compression are as follow:

Volumetric efficiency increases as result of lower delivery pressure in the L.P. cylinder clearance space. As compression being approximated to isothermal. Power required to drive the compressor reduces. Better mechanical balance and uniform torque. Also reduced size of fly wheel.Maximum temperature in the cycle is reduced thus less difficulty in lubrication.

leakage loss owing to reduced pressure difference on piston and valves. Reduced weight of cylinders.

cts (Reduces) Volumetric Efficiency


an intercooler where heat from the air is rejected by cooling intake temperature of L.P. it is called as

cooled air is admitted in to In H.P. stage it is compressed polytropic ally along curve 2 –

overlapped we will get combined is single stage compression with law PVn = C.

3 – P3 – P2 therefore in work with two stage compressor with perfect

intercooling. When cooling is perfect, Point 2 will lie on isothermal curve (T1 = T2) as

result of lower delivery pressure in the L.P.

being approximated to isothermal. Power required to drive the

reduced size of fly wheel. Maximum temperature in the cycle is reduced thus less difficulty in lubrication.

leakage loss owing to reduced pressure difference on either sides of the


Page | 58

(1) Mainly volumetric efficiency depends on clearance. As clearance volume increases volumetric efficiency decreases.

(2) Restricted passage and leakage at inlet valves. (3) Piston ring leakage. (4) If the speed of rotation is high charge of air taken in is less which decreases

efficiency. (5) Fresh air comes in contact with hot wall and gets expanded which decrease the

charge taken in therefore volumetric efficiency.

• Rotary Compressor In reciprocating air compressor the pressure of air is increased in cylinder with the

help of moving piston whereas in a rotary compressor, the air is entrapped between two sets to engaging surface and the pressure of air is increased by squeezing action of air.

Rotary compressors may be classified as: (A) Positive Displacement Compressors. (B) Non-positive Displacement Compressors.

Rotary Compressor

Positive Displacement Non-positive Displacement Compressor compressor Roots Vane Lysholm Screw Centrifugal Axial flow Blower type compressor type

• Roots Blower Refer Fig. 3.16. It consist of two rotors driven externally. One of the rotor is connected

to the drive and the second one is gear driven from the first. The rotors have got two or three lobes having epicycloid, hypocycloid, involute profiles. The high pressure delivery side is sealed from the low pressure suction side at all angular positions. A very small clearance is maintained between the surfaces to prevent wear. Air leakage through the clearance decreases the efficiency as pressure ratio increases.

Working: During rotation volume of air V at atmospheric pressure Pbetween the left hand rotor and the casing. This air is positively displaced with change in volume until the space open to high pressure region. At this instant some high pressure air rushes back from the receiver and mix irreversibly with blowequalised. Assuming the receiver to be of infinite size the pressure equalised to the receiver pressure P2. The air is then delivered to the receiver. This happens four times with two lobe rotor and six times with three lobe is 4 V per revolution. It should be noted that the delivery of air into the receiver is not continuous. Even though the rotors revolve with uniform speed.

The work done per revolution of

W.D = (P2

This work is greater than the work required to drive a reversible adiabatic compression.

• Vane Type Blower Refer to Fig. 7.17. It consists of a rotor located eccentrically in a cylindrical outer casing.

The rotor carries a set of spring loaded vanes in the slots of the rotor. Refer P shown in Fig. 7.17. The volume


Working: During rotation volume of air V at atmospheric pressure Pbetween the left hand rotor and the casing. This air is positively displaced with change in volume until the space open to high pressure region. At this instant some high pressure air

the receiver and mix irreversibly with blower air V until the pressure is equalised. Assuming the receiver to be of infinite size the pressure equalised to the receiver

. The air is then delivered to the receiver. This happens four times with two lobe rotor and six times with three lobe rotor. Therefore the free air delivered for two

V per revolution. It should be noted that the delivery of air into the receiver is not continuous. Even though the rotors revolve with uniform speed.

The work done per revolution of rotor

2 – P1) 4V

This work is greater than the work required to drive a reversible adiabatic

Refer to Fig. 7.17. It consists of a rotor located eccentrically in a cylindrical outer

The rotor carries a set of spring loaded vanes in the slots of the rotor. Refer P shown in Fig. 7.17. The volume


Working: During rotation volume of air V at atmospheric pressure P1 is trapped between the left hand rotor and the casing. This air is positively displaced with change in volume until the space open to high pressure region. At this instant some high pressure air

er air V until the pressure is equalised. Assuming the receiver to be of infinite size the pressure equalised to the receiver

. The air is then delivered to the receiver. This happens four times with two lobe rotor. Therefore the free air delivered for two lobe rotor

V per revolution. It should be noted that the delivery of air into the receiver is not

This work is greater than the work required to drive a reversible adiabatic

Refer to Fig. 7.17. It consists of a rotor located eccentrically in a cylindrical outer

The rotor carries a set of spring loaded vanes in the slots of the rotor. Refer P – V diagram

of air V1 atmospheric pressure Pproceeds the trapped air is first compressed reversibly from condition 1 to d, the compression takes place due to the decrease in volume provided for the trapped air. Then the air is compressed irreversibly frirreversible compression is similar to the compression explained in roots blower. The type compressor require less work compared to roots blower for the pressure rise. Normally vane typeminute at pressure ratios up to 8.5. The speed of the vane type blower is limited to about 30,000 r.p.m.

The vane type and roots blowers are replaced by centrifugal compressors for their use in supercharging aero engines. This is because the centrifugal blowers are comparatively much more efficient, can be easily fitted into the design of aeromuch higher speeds and are much more efficient.

• Centrifugal CompressorThe basic elements of the centrifugal compressor are shown in Fig. 3.18. It consists of a

rotating member known as an ‘impeller’ is fitted on compressor shaft. An impeller has rotary vanes provides closed radial passages for flow of air. Atmospheric air is sucked in at the centre of the impeller called the ‘eye’. A diffuser ring, around the impwith diffuser vanes. In diffuser vanes the kinetic energy of air changes into pressure energy. The volute casing also provides diffuser passage for further built up of air pressure.


atmospheric pressure P1 is trapped between two vanes. As the rotation proceeds the trapped air is first compressed reversibly from condition 1 to d, the compression takes place due to the decrease in volume provided for the trapped air. Then the air is compressed irreversibly from the pressure Pd to deliver pressure Pirreversible compression is similar to the compression explained in roots blower. The type compressor require less work compared to roots blower for the pressure rise. Normally vane type compressors are used to deliver up to 150 m

pressure ratios up to 8.5. The speed of the vane type blower is limited to about

The vane type and roots blowers are replaced by centrifugal compressors for their use in supercharging aero engines. This is because the centrifugal blowers are comparatively much more efficient, can be easily fitted into the design of aero-engines can be much higher speeds and are much more efficient.

Centrifugal Compressor The basic elements of the centrifugal compressor are shown in Fig. 3.18. It consists of a

rotating member known as an ‘impeller’ is fitted on compressor shaft. An impeller has rotary vanes provides closed radial passages for flow of air. Atmospheric air is sucked in at the centre of the impeller called the ‘eye’. A diffuser ring, around the impwith diffuser vanes. In diffuser vanes the kinetic energy of air changes into pressure energy.

also provides diffuser passage for further built up of air pressure.


is trapped between two vanes. As the rotation proceeds the trapped air is first compressed reversibly from condition 1 to d, the compression takes place due to the decrease in volume provided for the trapped air. Then

to deliver pressure P2. The irreversible compression is similar to the compression explained in roots blower. The vane type compressor require less work compared to roots blower for the same capacity and

compressors are used to deliver up to 150 m3 of air per pressure ratios up to 8.5. The speed of the vane type blower is limited to about

The vane type and roots blowers are replaced by centrifugal compressors for their use in supercharging aero engines. This is because the centrifugal blowers are comparatively

engines can be driven at

The basic elements of the centrifugal compressor are shown in Fig. 3.18. It consists of a rotating member known as an ‘impeller’ is fitted on compressor shaft. An impeller has rotary vanes provides closed radial passages for flow of air. Atmospheric air is sucked in at the centre of the impeller called the ‘eye’. A diffuser ring, around the impeller, is provided with diffuser vanes. In diffuser vanes the kinetic energy of air changes into pressure energy.

also provides diffuser passage for further built up of air pressure.

As the impeller rotates at high accelerated to a high velocity. This air isbuilt its pressure. Finally the compressed air leaves through the outlet nozzle. These type of compressor supplied air usually in the pressure ratio range 1.1 to 2.4 and may be upto 4 when it is single stage multistage compressors the pressure ratiocompressors are used in turbojet engines, even furnaces and for pipe line flow and for super changing I.C. engines.

Refer to the Fig. 7.18(a) which represent the pressure and velocity variation in impeller and diffuser is shown.


impeller rotates at high speed air undergoes centrifugal action and is accelerated to a high velocity. This air is decelerated in the diffuser and volute casing to built its pressure. Finally the compressed air leaves through the outlet nozzle. These type of

r usually in the pressure ratio range 1.1 to 2.4 and may be upto 4 when it is single stage compressor. In case of increase in stage on same shaft, called multistage compressors the pressure ratio obtained ranges up to 11 to 15. Such type of

used in turbojet engines, even furnaces and for pipe line flow and for super

Refer to the Fig. 7.18(a) which represent the pressure and velocity variation in impeller and diffuser is shown.


speed air undergoes centrifugal action and is decelerated in the diffuser and volute casing to

built its pressure. Finally the compressed air leaves through the outlet nozzle. These type of r usually in the pressure ratio range 1.1 to 2.4 and may be upto 4

compressor. In case of increase in stage on same shaft, called obtained ranges up to 11 to 15. Such type of

used in turbojet engines, even furnaces and for pipe line flow and for super

Refer to the Fig. 7.18(a) which represent the pressure and velocity variation in

• Axial Flow CompressorAn axial flow compressor is a multistage unit as each stage builds up pressure by

small amount. The unit consist of a ring of fixed blades and a ring of moving blades. Moving blades are mounted on the rotor The blades are aerofoil shape for efficient working. Air flows through the annulus ring between the rotor and the stator As the rotor rotates air in the blades passage accelerate due to which velocity and pressure increases. The air then passes which velocity of air decreases and pressure increases, pressure rise in each order 12 to 15%. And the turbine planet.

• Comparison Between Centrifugal Air Compressor And Axial Flow Air Compressor (1) In centrifugal air compressor the pressure

delivery pressure is high but this compressor is not suitable for multithe losses in each stage are more.

(2) The efficiency of these over wide range of rotational speed is very high, of the order 70 to 80% whereas that of axial flow compressor is 50 to 60%.

(3) For starting low torque is required whereas as high starting torque is requirement of axial flow compressors.

(4) Centrifugal compressor are simple in manufacture and the cost is less as well it needs less floor space and is flexible.

(5) Ram efficiency of the axial flow compressor is high also it peak load.

(6) The centrifugal compressor is specially used for super changing I.C. engines, in turbojet engines, in refrigeration cycles etc. Theused in gas turbine plants.


Axial Flow Compressor An axial flow compressor is a multistage unit as each stage builds up pressure by

small amount. The unit consist of a ring of fixed blades and a ring of moving blades. Moving blades are mounted on the rotor while fixed blades are fixed on stator or casingThe blades are aerofoil shape for efficient working. Air flows through the annulus ring between the rotor and the stator over the blades, parallel to the axis of the compressor.

As the rotor rotates air in the blades passage accelerate due to which velocity and pressure increases. The air then passes through fixed blade passages of diffuser shape in which velocity of air decreases and pressure increases, pressure rise in each order 12 to 15%. And the number of stages used varies from 5 to 14. It is mainly used in gas

Comparison Between Centrifugal Air Compressor And Axial Flow Air

In centrifugal air compressor the pressure increased in each stage is high so the delivery pressure is high but this compressor is not suitable for multithe losses in each stage are more. The efficiency of these over wide range of rotational speed is very high, of the order

whereas that of axial flow compressor is 50 to 60%. For starting low torque is required whereas as high starting torque is requirement of axial flow compressors. Centrifugal compressor are simple in manufacture and the cost is less as well it

floor space and is flexible. Ram efficiency of the axial flow compressor is high also it gives high efficiency at

The centrifugal compressor is specially used for super changing I.C. engines, in turbojet engines, in refrigeration cycles etc. The axial flow compressors are widely used in gas turbine plants.


An axial flow compressor is a multistage unit as each stage builds up pressure by small amount. The unit consist of a ring of fixed blades and a ring of moving blades.

while fixed blades are fixed on stator or casing. The blades are aerofoil shape for efficient working. Air flows through the annulus ring

over the blades, parallel to the axis of the compressor. As the rotor rotates air in the blades passage accelerate due to which velocity and

through fixed blade passages of diffuser shape in which velocity of air decreases and pressure increases, pressure rise in each stage is of the

from 5 to 14. It is mainly used in gas

Comparison Between Centrifugal Air Compressor And Axial Flow Air

increased in each stage is high so the delivery pressure is high but this compressor is not suitable for multi-staging since

The efficiency of these over wide range of rotational speed is very high, of the order

For starting low torque is required whereas as high starting torque is requirement of

Centrifugal compressor are simple in manufacture and the cost is less as well it

gives high efficiency at

The centrifugal compressor is specially used for super changing I.C. engines, in axial flow compressors are widely


Page | 63

• Comparison Between Reciprocating Air Compressors And Rotary Air Compressors • Reciprocating compressors compresses air to high discharge pressure at low speed of

rotation but discharge is low. • Rotary compressor is continuous discharge type and needs no receiver but receiver is

essential for reciprocating compressor. • Balancing is perfect in case of rotary compressor whereas more vibrations and

imperfect balancing is problem of reciprocating compressor hence robust foundation is requirement.

• Rotary compressors are compact in design hence need less floor space and easy to handled. Reciprocating compressors are bulky.

• Reciprocating compressors has more number of moving parts in contact hence power is lost in friction and need lubrication whereas in rotary compressor less lubrication is required so more clean supply of air.

• Rotary compressors run at much higher speed and can be directly coupled to steam turbines, electric motor and high speed I.C. engines without gearing.

• Steam Generators• Introduction

Amongst a number of power share is contributed by thermal the working fluid, the generator of steam can be said to be heart of it. The steam generator is also known used in industries for different purposes,

1. For generation of electrical energy as in power plants.2. For generating mechanical energy in steam turbines.3. For process heating purpose as heating of ground nuts in

Mills. 4. For sizing and bleaching in textile industries.

Normally a boiler produces steam at high pressure. This steam is first used to drive turbines for generating power. Then the steam exhausted from turbines, which is at lower pressure is used for process heating purpose. A typical boiler has two differentchamber. Pressure part is a closed vessel, strongly fabricated out of steel. This contains water in it. The combustionfire bricks. The fuel undergoes combustion in this combustion chamber producing high temperature gases. These gases are also known as flue gases, hot furnace gases, or products of combustion. When flue gases comgive their heat to water, causing generation of steam. After wards flue gases are exhausted high into the atmosphere through the chimney.

• Classification Boilers are mainly classified according to the following f1. By the relative position of flue gases and water (or tube contents).

a) Fire tube

In this case flue gases flow through the tubes, which are surrounded by the water which is to be eveported. Ex. Scotch marine boiler etc.

b) Water tube


Steam Generators

Amongst a number of power plants fulfilling the power requirements of the share is contributed by thermal power plants. As this type of power plant use steam at the working fluid, the generator of steam can be said to be heart of it.

The steam generator is also known as ‘Bolier’. The steam produced in the boiler is used in industries for different purposes,

For generation of electrical energy as in power plants. For generating mechanical energy in steam turbines.

process heating purpose as heating of ground nuts in Oil.

For sizing and bleaching in textile industries.

Normally a boiler produces steam at high pressure. This steam is first used to drive turbines for generating power. Then the steam exhausted from turbines, which is at lower pressure is used for process heating purpose.

A typical boiler has two different parts known as pressure part and combustion chamber. Pressure part is a closed vessel, strongly fabricated out of steel. This contains

combustion chamber in constructed around pressure part with help of fire bricks. The fuel undergoes combustion in this combustion chamber producing high temperature gases. These gases are also known as flue gases, hot furnace gases, or products of combustion. When flue gases come in contact with the water container, they give their heat to water, causing generation of steam. After wards flue gases are exhausted high into the atmosphere through the chimney.

Boilers are mainly classified according to the following factors By the relative position of flue gases and water (or tube contents).

In this case flue gases flow through the tubes, which are surrounded by the water which is to be eveported. Ex. Lancashire, Cornish, Cochran, Locomotive, Simple


plants fulfilling the power requirements of the world, major power plants. As this type of power plant use steam at

the working fluid, the generator of steam can be said to be heart of it. as ‘Bolier’. The steam produced in the boiler is

Normally a boiler produces steam at high pressure. This steam is first used to drive turbines for generating power. Then the steam exhausted from turbines, which is at

parts known as pressure part and combustion chamber. Pressure part is a closed vessel, strongly fabricated out of steel. This contains

onstructed around pressure part with help of fire bricks. The fuel undergoes combustion in this combustion chamber producing high temperature gases. These gases are also known as flue gases, hot furnace gases, or

e in contact with the water container, they give their heat to water, causing generation of steam. After wards flue gases are

By the relative position of flue gases and water (or tube contents).

In this case flue gases flow through the tubes, which are surrounded by the water Lancashire, Cornish, Cochran, Locomotive, Simple vertical,

In this case water flows through the tubes and hot gases heat the tubes from out side. Ex. Babock Wilcox, Stirling Boiler.

2. By the method of firinga) Internally fired: In this case the furnace is located

case of Lancashire boiler.

b) Externally fired: The furnace is located outside the boiler shell as in case of Babcock Wilcox boiler.

[please see fig. on next page]

3. According to pressure of steam

a) Low pressure Lancashire, Cochran, Cornish etc.

b) High pressure boilers: Boilers which can develop pressures above 80 bar. Ex. Babcock, Lamount, Velox, Benson etc.

4. Nature of Draught:sufficient quantity of air for combustion.a) Natural draught: In this case the draught is produced by means of chimney only.

The amount of draught directly depends upon the height of chimney.b) Artificial draught:

i) Induced Draught: Induced Draught is produced by sucking the flue gases from chamber. It is obtained by providing a fan between the boiler and the chimney.

ii) Forced Draught: Forcecombustion chamber w

iii) Balanced Draught: Balanced draught is produced by means of I.D. fan and F.D. fan.


In this case water flows through the tubes and hot gases heat the tubes from out side. Ex. Babock Wilcox, Stirling Boiler.

By the method of firing Internally fired: In this case the furnace is located inside the boiler shell as in case of Lancashire boiler.

Externally fired: The furnace is located outside the boiler shell as in case of Babcock Wilcox boiler.

[please see fig. on next page]

According to pressure of steam Low pressure boilers: Boilers which can develop pressures below 80 bar. Ex. Lancashire, Cochran, Cornish etc. High pressure boilers: Boilers which can develop pressures above 80 bar. Ex. Babcock, Lamount, Velox, Benson etc.

Nature of Draught: Draught is the pressure difference, which is necessary to draw sufficient quantity of air for combustion.

draught: In this case the draught is produced by means of chimney only. The amount of draught directly depends upon the height of chimney.Artificial draught: Artificial draught is produced by means of fans.

Induced Draught: Induced Draught is produced by sucking the flue gases from chamber. It is obtained by providing a fan between the boiler and the chimney. This fan is known as I.D. Fan. Forced Draught: Forced draught is produced by forcing the air into the combustion chamber w2ith the help of a fan, known as F.D. fan.Balanced Draught: Balanced draught is produced by means of I.D. fan and F.D. fan.


In this case water flows through the tubes and hot gases heat the tubes from out side.

inside the boiler shell as in

Externally fired: The furnace is located outside the boiler shell as in case of

boilers: Boilers which can develop pressures below 80 bar. Ex.

High pressure boilers: Boilers which can develop pressures above 80 bar. Ex.

fference, which is necessary to draw

draught: In this case the draught is produced by means of chimney only. The amount of draught directly depends upon the height of chimney.

Artificial draught is produced by means of fans. Induced Draught: Induced Draught is produced by sucking the flue gases from chamber. It is obtained by providing a fan between the boiler and

d draught is produced by forcing the air into the ith the help of a fan, known as F.D. fan.

Balanced Draught: Balanced draught is produced by means of I.D. fan

5. Method of circulation of water

a) Natural circulation: In b) Forced circulation: In which the circulation of water is obtained by a centrifugal

pump.

6. By the use, a) Land type: Boilers used with stationary plants.b) Marine type c) Locomotive boilers.

7. By the Design of flue

pass of multi pass.8. By the number of drums:9. According to energy source (fuel) used

The heat energy may be derived from,a) Combustion of fossile fuels as b) Electric or Nuclear energyc) Hot waste gases of other chemical reactions.

10. According to the material of construction of the boiler shella) Steel Boilers: Power boilers are generally fabricated b) C.I. Boilers: Low pressure boilers are some times built from cast iron.

• Lancashire Boiler It is a Fire tube, Stationary, Horizontal straight tube, Internally fired, Natural

circulation boiler. Normal working pressure in this boiler is about 15 bar and steam generation capacity and is upto 8T/hr.

Legend:

1. Dead wf. Safety valve.2. High steam low water alarm.3. Manhole.4. Steam stop valve and 5. Pressure gauge.6. Water level Indicator.7. Feed check valve and perforated feed pipe.


Method of circulation of water Natural circulation: In which the circulation of water is due to gravity.Forced circulation: In which the circulation of water is obtained by a centrifugal

Land type: Boilers used with stationary plants.

Locomotive boilers.

By the Design of flue gas passages: The flue gas may follow a single pass of multi pass. By the number of drums: There are 2 types, a) Single drum by Multi drum boilers.According to energy source (fuel) used The heat energy may be derived from,

Combustion of fossile fuels as coal, wood, oil or natural gas etc. Electric or Nuclear energy Hot waste gases of other chemical reactions.

According to the material of construction of the boiler shell Steel Boilers: Power boilers are generally fabricated out of steel plates.C.I. Boilers: Low pressure boilers are some times built from cast iron.

It is a Fire tube, Stationary, Horizontal straight tube, Internally fired, Natural circulation boiler. Normal working pressure in this boiler is about 15 bar and steam generation capacity and is upto 8T/hr.

Dead wf. Safety valve. steam low water alarm.

Manhole. Steam stop valve and Atipriming Device. Pressure gauge. Water level Indicator. Feed check valve and perforated feed pipe.


lation of water is due to gravity. Forced circulation: In which the circulation of water is obtained by a centrifugal

The flue gas may follow a single pass, return

There are 2 types, a) Single drum by Multi drum boilers.

coal, wood, oil or natural gas etc.

out of steel plates. C.I. Boilers: Low pressure boilers are some times built from cast iron.

It is a Fire tube, Stationary, Horizontal straight tube, Internally fired, Natural circulation boiler. Normal working pressure in this boiler is about 15 bar and steam

8. Flue tubes.9. Boiler shell.10. Fire bars.11. Brick work Bri12. Bottom flue.13. Side flues.14. Main flue.15. Blow-off 16. Blow-off pit.17. Gusset stays.18. Fusible tray.19. Scum tray.20. Scum valve.21. End plate.

Constructional Details:The main parts of the boiler are,1. Boiler drum: This boiler consists of a very large boiler drum. The size of the

boiler drum is approximately 7type of boiler, in this boiler, the meeting edges of the plate are connected by means of rivetted joints. Steel plates are rolled to form shell and the meeting edgesconnected by means of rivetted that the larger shells of required length can be obtained by inserting one shell into the other and rivetting over the circumference.

The end plates of the boiler are flat. These flat end plates, when they are subjected to steam pressure from inside they will have a tendencyfrom bulging, they are strengthened by means of stays. There are 2 types of stays.

i) Longitudinal stay: It to the order and are connected to the end plates by means of lock nuts.

ii) Diagonal Gusset stay: Consists of a triangular plate, which is rivetted to the shell plate and end pla

2. Fire tubes or flue tubes:each of fire tubes is corrugated, so as to take up expansion and contraction when the boiler gets hot and cold. These tubes are also made of number of shells. The ends of each of the shell are flanged outwards and the flanges of the twoconnected by means of rivets, so as to get shells of required length.


Flue tubes. Boiler shell. Fire bars. Brick work Bridge. Bottom flue. Side flues. Main flue.

off cock. off pit.

Gusset stays. Fusible tray. Scum tray. Scum valve. End plate.

Constructional Details: The main parts of the boiler are,

Boiler drum: This boiler consists of a very large boiler drum. The size of the boiler drum is approximately 7-9 mts in length and 2-3 mts in diameter. This is a very type of boiler, in this boiler, the meeting edges of the plate are connected by means of rivetted joints. Steel plates are rolled to form shell and the meeting edgesconnected by means of rivetted joints. The alternate shells are made smaller in diameter, so that the larger shells of required length can be obtained by inserting one shell into the other and rivetting over the circumference.

tes of the boiler are flat. These flat end plates, when they are subjected to steam pressure from inside they will have a tendency to bulge out. In order to prevent them from bulging, they are strengthened by means of stays. There are 2 types of stays.

Longitudinal stay: It consists of round bar which extends from one end plate to the order and are connected to the end plates by means of lock nuts.Diagonal Gusset stay: Consists of a triangular plate, which is rivetted to the shell plate and end plate as shown.

Fire tubes or flue tubes: Through the boiler drum passes 2 fire tubes. each of fire tubes is corrugated, so as to take up expansion and contraction when the boiler gets hot and cold. These tubes are also made of number of shells. The ends of each of the shell are flanged outwards and the flanges of the twoconnected by means of rivets, so as to get shells of required length.


Boiler drum: This boiler consists of a very large boiler drum. The size of the 3 mts in diameter. This is a very old

type of boiler, in this boiler, the meeting edges of the plate are connected by means of rivetted joints. Steel plates are rolled to form shell and the meeting edges of the shell are

joints. The alternate shells are made smaller in diameter, so that the larger shells of required length can be obtained by inserting one shell into the other

tes of the boiler are flat. These flat end plates, when they are subjected to In order to prevent them

from bulging, they are strengthened by means of stays. There are 2 types of stays.

consists of round bar which extends from one end plate to the order and are connected to the end plates by means of lock nuts. Diagonal Gusset stay: Consists of a triangular plate, which is rivetted to the

Through the boiler drum passes 2 fire tubes. Part of each of fire tubes is corrugated, so as to take up expansion and contraction when the boiler gets hot and cold. These tubes are also made of number of shells. The ends of each of the shell are flanged outwards and the flanges of the two-adjacent shells are connected by means of rivets, so as to get shells of required length.


Page | 68

It is to be noted that, the centre line of fire tubes is slightly below that of the centre line of boiler shell. Because fire tubes are provided approximately in the centre of water, so that heat can be transferred uniformly in all directions.

3. Grate, Brickwork Bridge etc.: Combustion of fuel takes place over the Grate. Top surface of the grate is made up of Fire-bars. Below the great Ash-pit in provided.

When the combustion of fuel takes place, hot gases are generated and the Brickwork bridge deflects the gases to move upwards.

4. Manhole: It gives access to the inside of the boiler drum. It will be sufficiently large enough for a man to pass through it, for cleaning and inspection purpose.

5. Mountings: This boiler is fitted with various mountings. Mountings are necessary for the safe and efficient operation of the boiler. The term mountings refers to the items such as, i) Safety valves: a) Dead weight

b) High steam low water alarm

When the pressure of steam in the boiler drum increases beyond safe value, then these valves will open and allow the surplus steam to escape to the atmosphere, till the pressure of steam in the boiler drum comes to normal working pressure.

ii) Pressure gauge: It indicates pressure inside the boiler drum. iii) Feed check valve: Water enters the boiler drum through feed check valve.

On the inner side of the feed check valve, perforated feed pipe is fitted for feeding the water uniformly in the boiler drum. Below the feed pipe, scum tray is fitted which separates scum and is removed through the scum valve.

iv) Water level indicator: It indicates the water level in the drum. v) Blow-off value: It blow out impurities due to gravity. vi) Steam stop valve: Through this steam will be taken out for use. vii) Anti priming device

It is always desirable that the steam should leave the boiler as dry as possible, for that purpose on anti priming device or steam collecting pipe is provided in the steam space. It consists of a pipe and rectangular openings are provided in its bottom surface. It is fitted by means of baffles from inside. When the wet steam (steam and water particles) enters the pipes, the water particles being heavier than steam, after striking the baffles fall back to water space and steam almost dry will be taken out through the steam stop valve.

6. Accessories: Accessories are used for improving the efficiency of boiler plant. Generally Super heater and Economiser are used as accessories.

7. Path of flue gases: When the combustion of fuel takes place, hot gases are generated and the brick work bridge deflects these gases to move upwards. During their first pass, these gases flow from the front end of the boiler to the rear end through central tubes. During their I-pass, flue gases heat the water from centre outwards. After their I-pass, they pass through the superheater, then enter the common bottom flue at the rear end. Now their II-pass starts, during this gases flow from rear end to front end through the common bottom flue. At the end of II-pass, the gases are bifurcated into two side flued, when the flue gases enter side flues, their III-pass starts and during their


Page | 69

III-pass, they flow from the front end to rear end through side flues and during this pass they heat the water from sides. After their third pass they meet in main common flue, from where they pass through the economiser and then they are exhausted through the chimney.

• Boiler Mountings And Accessories • Mountings

Mountings are the fittings mounted on the pressure part of the boiler, Mountings are necessary for the safe and efficient operation of the boiler without mountings boiler cannot work safely. Special provisions are made on the pressure part to mount the mountings. The term mountings refers to the items such as,

1. Safety valves a) Dead weight safety valve b) Spring loaded safety valve c) Lever safety valve d) High steam and low water alarm.

2. Water level indicators 3. Fusible plug 4. Pressure gauges 5. Steam stop valve 6. Feed check valve 7. Blow-off valve etc.

The above mountings are usually installed in accordance with IBR.

• Accessories Accessories are used to improve the efficiency of the boiler plant. Without accessories

boiler can work safely. These are not mounted on the boiler, but these are connected in the boiler circuit. Usually following accessories are provided with the boiler.

1. Super heater 2. Economiser 3. Air-preheater 5. Steam injector 5. Feed pump 6. Steam trap

• Dead Weight Safety Valve

As the name implies, this valve is used to assure safe working of the boiler. When the pressure of steam inside the boiler drum increases beyond the safe value, it may cause damage to the pressure part, or even a severe accident. It can be prevented surplus steam to escape to the atmosphere, by means of the safety valve.

This valve was first introduced by M/s J.J. Hopkinson and Co. Ltd. It central vertical pipe ‘A’, bottom end of which is flanged and mounted on the mounting blocks of the boiler. ‘B’ is the Gun metal valve, resting over the valve seat ‘C’. Valve seat ‘C’ is fixed on the top of the pipe ‘A’ by means of a securing ring and screw. ‘F’ is the feather which guides the valve B. Valvsteam discharge casing. The weight carrier is suspended from the top of the valve ‘B’weights are placed on the

Weight of the valve ‘B’, spindle, carrier, dead weights & cover will be acting downwards. During normal working conditions, this downward acting load will be balanced by the steam pressure from below. When the steam pressure exceeds prespecified or safe value, then the valve will be lifted up & the surplus steam will be exhausted to the atmosphere.

Ex. Dead weight safety value used on pressure cookers.

• High Steam Low Water Alarm[Please see fig. on next page This valve was also introduced by M/s Hopkinsovalve, i.e. it consists of 2 valves.

(i) High steam valve:surplus steam to escape to the atmosphere.


Dead Weight Safety Valve

As the name implies, this valve is used to assure safe working of the boiler. When the pressure of steam inside the boiler drum increases beyond the safe value, it may cause damage to the pressure part, or even a severe accident. It can be prevented surplus steam to escape to the atmosphere, by means of the safety valve.

This valve was first introduced by M/s J.J. Hopkinson and Co. Ltd. It central vertical pipe ‘A’, bottom end of which is flanged and through this flanged mounted on the mounting blocks of the boiler. ‘B’ is the Gun metal valve, resting over the

seat ‘C’ is fixed on the top of the pipe ‘A’ by means of a securing ring and screw. ‘F’ is the feather which guides the valve B. Valve ‘B’ is also guided by a ring in steam discharge casing. The weight carrier is suspended from the top of the valve ‘B’

s are placed on the weight carrier and these are covered by the Cast Iron cover.

Weight of the valve ‘B’, spindle, carrier, dead weights & cover will be acting downwards. During normal working conditions, this downward acting load will be balanced by the steam pressure from below. When the steam pressure exceeds prespecified or safe

lue, then the valve will be lifted up & the surplus steam will be exhausted to the

Ex. Dead weight safety value used on pressure cookers.

High Steam Low Water Alarm on next page]

This valve was also introduced by M/s Hopkinson and Co Ltd. This is a twoconsists of 2 valves.

High steam valve: During high steam conditions this valve opens and allows surplus steam to escape to the atmosphere.


As the name implies, this valve is used to assure safe working of the boiler. When the pressure of steam inside the boiler drum increases beyond the safe value, it may cause damage to the pressure part, or even a severe accident. It can be prevented by allowing the

This valve was first introduced by M/s J.J. Hopkinson and Co. Ltd. It consists of a through this flanged end it is

mounted on the mounting blocks of the boiler. ‘B’ is the Gun metal valve, resting over the seat ‘C’ is fixed on the top of the pipe ‘A’ by means of a securing ring

e ‘B’ is also guided by a ring in steam discharge casing. The weight carrier is suspended from the top of the valve ‘B’. Dead

weight carrier and these are covered by the Cast Iron cover.

Weight of the valve ‘B’, spindle, carrier, dead weights & cover will be acting downwards. During normal working conditions, this downward acting load will be balanced by the steam pressure from below. When the steam pressure exceeds prespecified or safe

lue, then the valve will be lifted up & the surplus steam will be exhausted to the

n and Co Ltd. This is a two-in-one

high steam conditions this valve opens and allows

(ii) Low water valve:

level, then this valve opens and allows the steam to escape. When the steam is allowed to escape, it makes whistling sound, i.e. it gives warning to the boiler attendant. The whistling sound for high steam conditions will be louder than low water condition, so that one can distinguish between the two. As shown in fig., ‘A’‘B’ in secured in position by means of a ring and feather ‘S’ is cast on it. This feather guides the valve A. ‘C’ is the low water valve, which is resting over the inner edge of the valve ‘A’ as shown ‘R’ is the rib which guides the valve ‘C’. Low water valve which is connected to the rod ‘E’, which is continuation to the spindle of the valve ‘C’. Valve ‘A’ is partly held in position by mans of the weight ‘D’ and partly by means of weight and counter weight outside the steam discharge casing.

In the steam space lever ‘FK’ is provided. A large fire brick float ‘L’ is suspended from the end ‘K’.

During normal working conditions, the float will be sub merged in waterweight of this float in partly balanced by means of counter weight ‘M’of buoyant force due to water, which is acting in the upward direction. But when the water level goes below the safe level, the float gets uncovered by meanbe buoyant force and counter weight. ‘M’ alone will not be sufficient to balance the float.


water valve: When the water level in the boiler drum falls below the level, then this valve opens and allows the steam to escape. When the steam is allowed to escape, it makes whistling sound, i.e. it gives warning to the boiler attendant. The whistling

r high steam conditions will be louder than low water condition, so that one can distinguish between the two. Since it makes whistling sound it is known as alarm.

As shown in fig., ‘A’ is the high steam valve, resting over valve seat ‘B’. in secured in position by means of a ring and feather ‘S’ is cast on it. This feather guides

the valve A. ‘C’ is the low water valve, which is resting over the inner edge of the valve ‘A’ as shown ‘R’ is the rib which guides the valve ‘C’.

‘C’ will be held in position by means of the Dead weight, ‘D’ which is connected to the rod ‘E’, which is continuation to the spindle of the valve ‘C’. Valve ‘A’ is partly held in position by mans of the weight ‘D’ and partly by means of

r weight outside the steam discharge casing.

steam space lever ‘FK’ is provided. A large fire brick float ‘L’ is suspended

During normal working conditions, the float will be sub merged in waterweight of this float in partly balanced by means of counter weight ‘M’ and partly by means of buoyant force due to water, which is acting in the upward direction. But when the water level goes below the safe level, the float gets uncovered by means of water, then there won’t be buoyant force and counter weight. ‘M’ alone will not be sufficient to balance the float.


When the water level in the boiler drum falls below the safe level, then this valve opens and allows the steam to escape. When the steam is allowed to escape, it makes whistling sound, i.e. it gives warning to the boiler attendant. The whistling

r high steam conditions will be louder than low water condition, so that one can Since it makes whistling sound it is known as alarm. is the high steam valve, resting over valve seat ‘B’. Valve seat

in secured in position by means of a ring and feather ‘S’ is cast on it. This feather guides the valve A. ‘C’ is the low water valve, which is resting over the inner edge of the valve ‘A’

‘C’ will be held in position by means of the Dead weight, ‘D’ which is connected to the rod ‘E’, which is continuation to the spindle of the valve ‘C’. Valve ‘A’ is partly held in position by mans of the weight ‘D’ and partly by means of

steam space lever ‘FK’ is provided. A large fire brick float ‘L’ is suspended

During normal working conditions, the float will be sub merged in water and the and partly by means

of buoyant force due to water, which is acting in the upward direction. But when the water s of water, then there won’t

be buoyant force and counter weight. ‘M’ alone will not be sufficient to balance the float.

So, the lever FK tills in the clockwise direction. Then the knife edge projection of the lever ‘FK’ comes in contact with the collaWhen the valve ‘C’ is lifted, steam escapes and makes whistling sound.

During high steam conditions, both the valves are lifted, since the low water valve is resting over inner edge of the high steam val

• Water Level IndicatorIt indicates the water level inside

visible from the boiler room floor by using mirrors. This unit was also introduced by M/s Hopkinson and Co. Ltd

The unit consists of two hollow gunstuffing box will be flanged and through this flanged end it is connected to the front end plate of the boiler. Upper stuffing box is connected to the steam box is connected to the water space. In between the two sfitted. (In between the glass and metal, rubber packing is provided in order to have gas tight joint)

Thus two valves A and B which contrboiler and the glass tube. When these valves are open, the handles are vertical and the water level in the glass tube will be the water level in the boiler drum. A third valve ‘C’ called as Blow-off valve is generally closed. When this valve is closed, its handle is vertical and to blow out sediments and impurities handle is to be made horizontal.

An arrangement is also provided, in order to shut off automatically the steam and water to the glass tube,arrangement consists of a hollow gun

During normal working conditions these balls will be in position shown by full circles. If the glass tube breaks, the rush of wa


lever FK tills in the clockwise direction. Then the knife edge projection of the lever comes in contact with the collar ‘N’ and in turn lifts the hemispherical valve ‘C’.

valve ‘C’ is lifted, steam escapes and makes whistling sound.

During high steam conditions, both the valves are lifted, since the low water valve is resting over inner edge of the high steam valve, and surplus steam will be exhausted.

Water Level Indicator It indicates the water level inside the boiler drum. This water level can be made

visible from the boiler room floor by using mirrors. This unit was also introduced by M/s Hopkinson and Co. Ltd.

The unit consists of two hollow gun-metal stuffing boxes. One end of each of the stuffing box will be flanged and through this flanged end it is connected to the front end plate of the boiler. Upper stuffing box is connected to the steam space and lower stuffing box is connected to the water space. In between the two stuffing boxes a strong glass tube is fitted. (In between the glass and metal, rubber packing is provided in order to have gas tight

valves A and B which control the passage of steam and water between the boiler and the glass tube. When these valves are open, the handles are vertical and the water level in the glass tube will be the water level in the boiler drum. A third valve ‘C’ called as

nerally closed. When this valve is closed, its handle is vertical and to blow out sediments and impurities handle is to be made horizontal.

An arrangement is also provided, in order to shut off automatically the steam and water to the glass tube, if the glass tube breaks due to any reason. This arrangement consists of a hollow gun-metal column ‘D’ and two balls as shown.

During normal working conditions these balls will be in position shown by full circles. If the glass tube breaks, the rush of water in the bottom passage carries the ball into


lever FK tills in the clockwise direction. Then the knife edge projection of the lever r ‘N’ and in turn lifts the hemispherical valve ‘C’.

During high steam conditions, both the valves are lifted, since the low water valve is ve, and surplus steam will be exhausted.

the boiler drum. This water level can be made visible from the boiler room floor by using mirrors. This unit was also introduced by

metal stuffing boxes. One end of each of the stuffing box will be flanged and through this flanged end it is connected to the front end

space and lower stuffing a strong glass tube is

fitted. (In between the glass and metal, rubber packing is provided in order to have gas tight

ol the passage of steam and water between the boiler and the glass tube. When these valves are open, the handles are vertical and the water level in the glass tube will be the water level in the boiler drum. A third valve ‘C’ called as

nerally closed. When this valve is closed, its handle is vertical and to

An arrangement is also provided, in order to shut off automatically the supply of if the glass tube breaks due to any reason. This

metal column ‘D’ and two balls as shown.

During normal working conditions these balls will be in position shown by full ter in the bottom passage carries the ball into

the position shown by dotted circle and shuts off the supply of water. At the same time the steam rushing through the upper passage aided by the water rushing upwards through the column ‘D’ drives the ball insupply. The attendant then can safely close the valves A and B and can replace the tube.

Screw plugs provided at the end of stuffing boxed, give access for cleaning of passages. The glass tube is generally covered from the front and from sides by Guard glass in order to protect the boiler attendant from the flying fragments of glass tube, if it breaks.

• Fusible Plug Function: It actuates itself as the last resort,

falls below the minimum permissible water level. by the heat of steam, the plug drops out and the steam rushers into the combustion chamber and extinguishes the fire. and also warns the boiler attendantpermissible level.

Fusible plug is fitted on the combustion chamber crown, but in the drum. As shown in fig. 10.20 ‘A’ is the hollow gun metal plug screwed into the crown plate. ‘B’ is the second hollow gun metal screwed into the plug ‘A’ and ‘C’ is the third solid copper coplug. The inner surface of ‘B’ and outer surface of ‘C’ are grooved as shown,the fusible metal (either Tin or lead) is poured in between the lugs these two plugs are locked up together. Hexagonal flanges are provided to the plugs ‘B’ anrefitting purpose by using spanners.

Under normal working conditions, fusible plug will be covered by means of water in the drum. This water keeps the temperawhen due to any reason, water level in the drum falls below the minimum permissible water level, the plug gets uncovered from water and is exposed to steam. Due to heat of steam, fusible metal melts and copper plug drops and the steam rushes through the access into the combustion chamber and extinguishes the fire. The ribs provided on the inner side of the


the position shown by dotted circle and shuts off the supply of water. At the same time the steam rushing through the upper passage aided by the water rushing upwards through the column ‘D’ drives the ball into the position shown by dotted circle and shuts off the steam supply. The attendant then can safely close the valves A and B and can replace the tube.

Screw plugs provided at the end of stuffing boxed, give access for cleaning of is generally covered from the front and from sides by Guard glass

in order to protect the boiler attendant from the flying fragments of glass tube, if it breaks.

It actuates itself as the last resort, when the water level in the boifalls below the minimum permissible water level. As a result of which, fusible by the heat of steam, the plug drops out and the steam rushers into the combustion chamber and extinguishes the fire. Thus it safeguards the combustion chamber crown from burning and also warns the boiler attendant about the fall of water level in the drum below minimum

Fusible plug is fitted on the combustion chamber crown, but in the drum. As shown in fig. 10.20 ‘A’ is the hollow gun metal plug screwed into the crown plate. ‘B’ is the

metal screwed into the plug ‘A’ and ‘C’ is the third solid copper cosurface of ‘B’ and outer surface of ‘C’ are grooved as shown,

the fusible metal (either Tin or lead) is poured in between the lugs these two plugs are locked up together. Hexagonal flanges are provided to the plugs ‘B’ and ‘C’ for removal and refitting purpose by using spanners.

Under normal working conditions, fusible plug will be covered by means of water in the drum. This water keeps the temperature of the fusible metal below its melting point. But

reason, water level in the drum falls below the minimum permissible water level, the plug gets uncovered from water and is exposed to steam. Due to heat of steam, fusible metal melts and copper plug drops and the steam rushes through the access into the

mbustion chamber and extinguishes the fire. The ribs provided on the inner side of the


the position shown by dotted circle and shuts off the supply of water. At the same time the steam rushing through the upper passage aided by the water rushing upwards through the

to the position shown by dotted circle and shuts off the steam supply. The attendant then can safely close the valves A and B and can replace the tube.

Screw plugs provided at the end of stuffing boxed, give access for cleaning of is generally covered from the front and from sides by Guard glass

in order to protect the boiler attendant from the flying fragments of glass tube, if it breaks.

when the water level in the boiler drum As a result of which, fusible metal melts

by the heat of steam, the plug drops out and the steam rushers into the combustion chamber mber crown from burning

about the fall of water level in the drum below minimum

Fusible plug is fitted on the combustion chamber crown, but in the drum. As shown in fig. 10.20 ‘A’ is the hollow gun metal plug screwed into the crown plate. ‘B’ is the

metal screwed into the plug ‘A’ and ‘C’ is the third solid copper conical surface of ‘B’ and outer surface of ‘C’ are grooved as shown, so that when

the fusible metal (either Tin or lead) is poured in between the lugs these two plugs are d ‘C’ for removal and

Under normal working conditions, fusible plug will be covered by means of water in fusible metal below its melting point. But

reason, water level in the drum falls below the minimum permissible water level, the plug gets uncovered from water and is exposed to steam. Due to heat of steam, fusible metal melts and copper plug drops and the steam rushes through the access into the

mbustion chamber and extinguishes the fire. The ribs provided on the inner side of the

plug A, hold the plug otherwise the plthe boiler, the attendant removes and refits the plug after interposing the fubetween the plugs ‘B’ and ‘C’.

• Bourdon Pressure GaugeThis is most common type of pressure gauge. This is used to measure pressure ins

the containers and pipe lines etc.

The basic element of this gauge is the tube ‘A’. It is elliptical in cross section and is bent into an arc of circle as shown.

End ‘B’ of this tube is sealed, while open end ‘C’ is connected to the connunion ‘D’. Through the connecting union the gapipes, of whose pressures are to be measured.

When it is mounted on the systems and if the pressure of the system is more than atmosphere (i.e. + ve pressure)[then the tube will tend to curl out. Conversely if theof the system is less than the atmosphere, (i.e. therefore appear as a movement of the end ‘B’. This end ‘B’ is connected by means of a link ‘E’ to a quadrant gear ‘F’. The quadrant gear engages with a pointer ‘H’ is attached.

Thus then change of pressure will appear as the movement of the end ‘B’ which will be transmitted to the quadrant gar, which inturn rotate the pinion and hence the pointer. The pointer rotates over the calibrated scale, which directly gives the pressure re


plug A, hold the plug otherwise the plug fall into the combustion chamber. Before refiring the boiler, the attendant removes and refits the plug after interposing the fubetween the plugs ‘B’ and ‘C’.

Bourdon Pressure Gauge This is most common type of pressure gauge. This is used to measure pressure ins

the containers and pipe lines etc.

The basic element of this gauge is the tube ‘A’. It is elliptical in cross section and is bent into an arc of circle as shown.

End ‘B’ of this tube is sealed, while open end ‘C’ is connected to the connunion ‘D’. Through the connecting union the gauge will be mounted over the containers or pipes, of whose pressures are to be measured.

When it is mounted on the systems and if the pressure of the system is more than atmosphere (i.e. + ve pressure)[then the tube will tend to curl out. Conversely if theof the system is less than the atmosphere, (i.e. – ve pressure)] The change of pressure will therefore appear as a movement of the end ‘B’. This end ‘B’ is connected by means of a link ‘E’ to a quadrant gear ‘F’. The quadrant gear engages with a small gear ‘G’ on to which a

Thus then change of pressure will appear as the movement of the end ‘B’ which will be transmitted to the quadrant gar, which inturn rotate the pinion and hence the pointer. The pointer rotates over the calibrated scale, which directly gives the pressure re


ug fall into the combustion chamber. Before refiring the boiler, the attendant removes and refits the plug after interposing the fusible metal

This is most common type of pressure gauge. This is used to measure pressure inside

The basic element of this gauge is the tube ‘A’. It is elliptical in cross section and is

End ‘B’ of this tube is sealed, while open end ‘C’ is connected to the connecting uge will be mounted over the containers or

When it is mounted on the systems and if the pressure of the system is more than atmosphere (i.e. + ve pressure)[then the tube will tend to curl out. Conversely if the pressure

ve pressure)] The change of pressure will therefore appear as a movement of the end ‘B’. This end ‘B’ is connected by means of a link

small gear ‘G’ on to which a

Thus then change of pressure will appear as the movement of the end ‘B’ which will be transmitted to the quadrant gar, which inturn rotate the pinion and hence the pointer. The pointer rotates over the calibrated scale, which directly gives the pressure readings.

• Steam Stop Valve Through the steam stop

The function of the steam stop valve is to shut of steam from the flow of steam the boiler to the steam pipe or from the steam pipe to engine. When used for the former purposes, it is called Junction valve. Usually the junction valve means a regulating valve means a regulating valve of larger size & a stop valve refers to a regulsize.

The junction valve is mounted on the top most part of the steam space of the boiler and is connected to the steam pipe which carries the steam to the engine.

Figure shows the different part of a common type of steam stop valve. This valve body is usually made of C.I. has two flanges. One flange is bolted to the boiler at the highest point of the steam space and the other flange is connected to the steam outlet a spindle which passes through glands and stuffing box. necessary to make the valve leak proof. The upper portion of the spindle is threaded and it passage through a nut in a cross bar supported by the pillars screvalve. The valve disc rests on a valve seat. By rotating the hand wheel, the valve can be opened or closed.

• Feed Check Valve Through the feed check valve, water enters the boiler drum. It allows the water to flew

into the drum and it will not allow the heater to flow out of the drum, so it is called as a check valve.

• Blow off Valve Mud or any other settled impurities are blown out

• Superheater The steam generated from a simple low pressure boiler is generally wet. So for

superheating the steam, superheaters are used. In the superheater, wet steam is first dried at the same temperature and pressure and then it is superheated at constant pressure.


Through the steam stop valve, steam will be taken out for power generation purpose.

The function of the steam stop valve is to shut of steam from the flow of steam the boiler to the steam pipe or from the steam pipe to engine. When used for the former purposes, it is called Junction valve. Usually the junction valve means a regulating valve means a regulating valve of larger size & a stop valve refers to a regulating valve of smaller


Figure shows the different part of a common type of steam stop valve. This valve body is usually made of C.I. has two flanges. One flange is bolted to the boiler at the highest point of the steam space and the other flange is connected to the steam outlet a spindle which passes through glands and stuffing box. The glands and packing are necessary to make the valve leak proof. The upper portion of the spindle is threaded and it passage through a nut in a cross bar supported by the pillars screwed in the body of the valve. The valve disc rests on a valve seat. By rotating the hand wheel, the valve can be

Through the feed check valve, water enters the boiler drum. It allows the water to flew into the drum and it will not allow the heater to flow out of the drum, so it is called as a

Mud or any other settled impurities are blown out through this valve.

The steam generated from a simple low pressure boiler is generally wet. So for superheating the steam, superheaters are used. In the superheater, wet steam is first dried at the same temperature and pressure and then it is superheated at constant pressure.


out for power generation purpose.

The function of the steam stop valve is to shut of steam from the flow of steam from the boiler to the steam pipe or from the steam pipe to engine. When used for the former purposes, it is called Junction valve. Usually the junction valve means a regulating valve

ating valve of smaller


Figure shows the different part of a common type of steam stop valve. This valve body is usually made of C.I. has two flanges. One flange is bolted to the boiler at the highest point of the steam space and the other flange is connected to the steam outlet pipe. There is

The glands and packing are necessary to make the valve leak proof. The upper portion of the spindle is threaded and it

wed in the body of the valve. The valve disc rests on a valve seat. By rotating the hand wheel, the valve can be

Through the feed check valve, water enters the boiler drum. It allows the water to flew into the drum and it will not allow the heater to flow out of the drum, so it is called as a

The steam generated from a simple low pressure boiler is generally wet. So for superheating the steam, superheaters are used. In the superheater, wet steam is first dried at the same temperature and pressure and then it is superheated at constant pressure.

Generally, same heat of the flue gases is used for superheating purpose and hence superheaters are placed in the path of flue gases. However in bigger installations superheaters are provided with independent furnaces.

• Advantages of Superheating the 1. Increase in amount of work output, for the same amount of steam and hence increase

in cycle efficiency.2. Loss due to condensation of steam in the pipe line connecting the boiler to the steam

engine or steam turbine is reduced.3. Loss due to condensation4. When the superheated steam is used, moisture will be absent, hence it will reduce

corrosion and erosion of steam engine and steam turbine parts.

Fig. 10.23 shows Sudgen’s Hair pin type of superheater arranged with Lancashire / Cornish boiler. The superheater is placed at the back end of the boiler and the flue after their first pass, they pass through the superheater.

Here the temperature of flue gases is not less than 550superheat of 40 to 95o C

This superheater consists of two Mild Steel boxes or Headers and a number of tubes bent to U-shape. The end of the tubes, in the headers will be either expanded or welded in order to have gas tight joint. Between front and rear header some space is providespace is covered by means of a cover. This gives access for cleaning / inspection and repair purpose.

As long as temperature of the flue gases is less than 550burning of tubes. But when the temperature increases delivery of steam from the boiler to the steam turbine through the superheater is suspfor a long time, then the following arrangements are made so as to protect the tubes from burning out.


Generally, same heat of the flue gases is used for superheating purpose and hence superheaters are placed in the path of flue gases. However in bigger installations superheaters are provided with independent furnaces.

s of Superheating the Steam Increase in amount of work output, for the same amount of steam and hence increase in cycle efficiency. Loss due to condensation of steam in the pipe line connecting the boiler to the steam engine or steam turbine is reduced. Loss due to condensation of steam in the steam engine / steam turbine is reduced.When the superheated steam is used, moisture will be absent, hence it will reduce corrosion and erosion of steam engine and steam turbine parts.

Fig. 10.23 shows Sudgen’s Hair pin type of superheater arranged with Lancashire / Cornish boiler. The superheater is placed at the back end of the boiler and the flue after their first pass, they pass through the superheater.

flue gases is not less than 550o C. This superheater gives a

This superheater consists of two Mild Steel boxes or Headers and a number of tubes shape. The end of the tubes, in the headers will be either expanded or welded in

order to have gas tight joint. Between front and rear header some space is providespace is covered by means of a cover. This gives access for cleaning / inspection and repair

As long as temperature of the flue gases is less than 550o C then there is no danger of burning of tubes. But when the temperature increases beyond this and also when the delivery of steam from the boiler to the steam turbine through the superheater is suspfor a long time, then the following arrangements are made so as to protect the tubes from


Generally, same heat of the flue gases is used for superheating purpose and hence superheaters are placed in the path of flue gases. However in bigger installations

Increase in amount of work output, for the same amount of steam and hence increase

Loss due to condensation of steam in the pipe line connecting the boiler to the steam

steam engine / steam turbine is reduced. When the superheated steam is used, moisture will be absent, hence it will reduce

Fig. 10.23 shows Sudgen’s Hair pin type of superheater arranged with Lancashire / Cornish boiler. The superheater is placed at the back end of the boiler and the flue gases

C. This superheater gives a

This superheater consists of two Mild Steel boxes or Headers and a number of tubes shape. The end of the tubes, in the headers will be either expanded or welded in

order to have gas tight joint. Between front and rear header some space is provided and this space is covered by means of a cover. This gives access for cleaning / inspection and repair

C then there is no danger of beyond this and also when the

delivery of steam from the boiler to the steam turbine through the superheater is suspended for a long time, then the following arrangements are made so as to protect the tubes from

1. Flooding the superheater tubes.

through the superheater again starts.2. Diverting the flow of flue gases. This is done by Damper ‘D’ which is operated by

means of handle ‘H’ An arrangement is also provided so as to pass the

to the main steam pipe as may be required. ‘M’ is the main steam pipe, PQ and R are stop valves. When the super heater is in action valves P and Q are open ‘R’ is closed. When steam is to be taken out directly from thclose and R is opened.

• Economiser One of the major heat losses in the boiler plant is the heat carried away by the

exhaust gasses. And economiser is a device or appliance, which recovers some of the heat of the exhaust gases. preheated water when it is supplied toconversion into steam. This reduces the amount of fuel required and thus the efficiency of boiler plant increases.

[Please see fig. on next pageFig. 10.24 shows the Green’s economiser. It is used with

boilers. It consists of a number of vertical pipes ‘A’. These pipes are arranged in groups of 4,

8, 12, 16, etc. Upper ends of the pipes are connected to the upper


superheater tubes. This water is to be, drained before the supply through the superheater again starts. Diverting the flow of flue gases. This is done by Damper ‘D’ which is operated by

is also provided so as to pass the steam through superheater or directly

to the main steam pipe as may be required. ‘M’ is the main steam pipe, PQ and R are stop valves. When the super heater is in action valves P and Q are open ‘R’ is closed. When steam is to be taken out directly from the boiler to the steam pipe, then valves P and Q are

One of the major heat losses in the boiler plant is the heat carried away by the exhaust gasses. And economiser is a device or appliance, which recovers some of the heat of the exhaust gases. This recovered heat in utilised for preheating the water.

water when it is supplied to the boiler drum, it requires less heat for its conversion into steam. This reduces the amount of fuel required and thus the efficiency of boiler plant increases.

Please see fig. on next page] Fig. 10.24 shows the Green’s economiser. It is used with stationary low pressure

It consists of a number of vertical pipes ‘A’. These pipes are arranged in groups of 4, , etc. Upper ends of the pipes are connected to the upper


This water is to be, drained before the supply of steam

Diverting the flow of flue gases. This is done by Damper ‘D’ which is operated by

steam through superheater or directly to the main steam pipe as may be required. ‘M’ is the main steam pipe, PQ and R are stop valves. When the super heater is in action valves P and Q are open ‘R’ is closed. When

e boiler to the steam pipe, then valves P and Q are

One of the major heat losses in the boiler plant is the heat carried away by the exhaust gasses. And economiser is a device or appliance, which recovers some of the

This recovered heat in utilised for preheating the water. This the boiler drum, it requires less heat for its

conversion into steam. This reduces the amount of fuel required and thus the efficiency

stationary low pressure

It consists of a number of vertical pipes ‘A’. These pipes are arranged in groups of 4,

boxes ‘B’. These boxes ‘B’ are inturn connected to the common header ‘D’. Lower ends of the pipes are connected to lower boxes. These lower boxes are pipe ‘C’ through the cross pipes. All the tubes are enclosed in theeconomiser except header ‘D’ and pipe ‘C’.

Water will be pumped by means of a feed pump, water enters the economiser through the stop valve at the inlet ‘F’ and passes into through the cross pipes and tprovided in the path of flue gases, the water rising through the tubes recovers heat and becomes hot. Hot water will be then collected into the top common header. This not water from the top header is taken out through the stop valve ‘H’, from where it goes to the boiler drum. ‘K’ is the safety valve for the economiser.

Since the economiser is provided in the path of flue gases, soot (or ash)be collected over the tubes. It retards the rate of heat transfer from inside the tubes. In order to avoid this, soot in scrapped by means of scrapestwo-adjacent tubes are coupled to form one pair connected by means of a chain, which passes over pulley ‘P’. Pulley ‘P’ is connected to worm wheel ‘W’, which is in turn driven by means of worm shaft, in such a way that when one pair of scrappers comes to top most positposition, then it automatically motion as long as the economiser is in action.

By pass arrangement: (fig. 10.25) By pass arrangements are provided for the flue gases and for feed water, so that the economiser may be put out of action when not required. Fig shows such an arrangement for two Lancashire boilers fitted with an economiserthe economiser is in service, then dampers ‘L’ and ‘M’ are open and the damper ‘N’ is closed. For isolating the economiser damper ‘N’ is opened and dampers ‘L’ and ‘M’ are closed.

• Air Preheater: The air is heated, by using the heat of flue gases inpreheater. Thus heat of the flue gases is also extracted in the Air perheater, which otherwise would have been lost to the atmosphere. By using Air per heater the overall efficiency will increase by about 10%


boxes ‘B’. These boxes ‘B’ are inturn connected to the common header ‘D’. Lower ends of the pipes are connected to lower boxes. These lower boxes are connected to the horizontal pipe ‘C’ through the cross pipes. All the tubes are enclosed in the brick work of the economiser except header ‘D’ and pipe ‘C’.

Water will be pumped by means of a feed pump, water enters the economiser through the stop valve at the inlet ‘F’ and passes into the pipe ‘C’, from where it flows through the cross pipes and then rises through the vertical tubes ‘A’. Since the economiser is provided in the path of flue gases, the water rising through the tubes recovers heat and becomes hot. Hot water will be then collected into the top common header. This not water

header is taken out through the stop valve ‘H’, from where it goes to the boiler drum. ‘K’ is the safety valve for the economiser.

the economiser is provided in the path of flue gases, soot (or ash)be collected over the tubes. It retards the rate of heat transfer from the flue gases to the water inside the tubes. In order to avoid this, soot in scrapped by means of scrapes

adjacent tubes are coupled to form one pair and two such pairs of scrapers are connected by means of a chain, which passes over pulley ‘P’. Pulley ‘P’ is connected to worm wheel ‘W’, which is in turn driven by means of worm shaft, in such a way that when one pair of scrappers comes to top most position, another pair will be at the bottom most position, then it automatically reverses the direction of motion. The scrapers are kept in motion as long as the economiser is in action.

By pass arrangement: (fig. 10.25) By pass arrangements are provided for the flue gases and for feed water, so that the economiser may be put out of action when not required.

shows such an arrangement for two Lancashire boilers fitted with an economiserthe economiser is in service, then dampers ‘L’ and ‘M’ are open and the damper ‘N’ is closed. For isolating the economiser damper ‘N’ is opened and dampers ‘L’ and ‘M’ are

The air is heated, by using the heat of flue gases in a device called Air preheater. Thus heat of the flue gases is also extracted in the Air perheater, which otherwise would have been lost to the atmosphere. By using Air per heater the overall efficiency will increase by about 10%


boxes ‘B’. These boxes ‘B’ are inturn connected to the common header ‘D’. Lower ends of connected to the horizontal

brick work of the

Water will be pumped by means of a feed pump, water enters the economiser the pipe ‘C’, from where it flows

hen rises through the vertical tubes ‘A’. Since the economiser is provided in the path of flue gases, the water rising through the tubes recovers heat and becomes hot. Hot water will be then collected into the top common header. This not water

header is taken out through the stop valve ‘H’, from where it goes to the boiler

the economiser is provided in the path of flue gases, soot (or ash) is likely to the flue gases to the water

inside the tubes. In order to avoid this, soot in scrapped by means of scrapes. Scrapers of the and two such pairs of scrapers are

connected by means of a chain, which passes over pulley ‘P’. Pulley ‘P’ is connected to worm wheel ‘W’, which is in turn driven by means of worm shaft, in such a way that when

ion, another pair will be at the bottom most reverses the direction of motion. The scrapers are kept in

By pass arrangement: (fig. 10.25) By pass arrangements are provided for the flue gases and for feed water, so that the economiser may be put out of action when not required.

shows such an arrangement for two Lancashire boilers fitted with an economiser. When the economiser is in service, then dampers ‘L’ and ‘M’ are open and the damper ‘N’ is closed. For isolating the economiser damper ‘N’ is opened and dampers ‘L’ and ‘M’ are

a device called Air preheater. Thus heat of the flue gases is also extracted in the Air perheater, which otherwise would have been lost to the atmosphere. By using Air per heater the overall

• Feed Pump: It is an applia

feed pump may be either rotary or reciprocating type.

• Steam Injector: When injects or pumps or delivers feed water to the boiler drum, by

• Steam Trap: It automaticalpartial condensation of steam, without allowing any seam to escape is known as steam trap.

• Boiler Draught • Draught is the pressure difference, which is necessary to draw the required quantity of

air for combustion and to remove the flue gases out Thus the object of producing draught in a boiler is,

i) To provide sufficient quantity of air for combustionii) To iii) To discharge these gases to the atmosphere, through the chimney.

Usually this drought (pressure difference) in boiler is of small magnitude and is measured in mm of water column by means of draught

Note: The amount of draught depends upon,

i) Nature and depth of fuel on the grate.ii) Design of combustion chamber/firebox.iii) Rate of combustion required.iv) Resistance offered in the system due to baffles, tubes,

Superheater,

• Classification Draught is broadly classified into 21. Natural or chimney 2. Artificial draught

(a) Fan Draught (Produced by Mechanical Fans)i) Forced draughtii) Induced draught


It is an appliance used to pump the feed water into the boiler drum. The feed pump may be either rotary or reciprocating type.

When the feed pump fails due to any reasons, then steam injector, injects or pumps or delivers feed water to the boiler drum, by the use of steam.

It automatically collects and returns to the boiler, the water resulting from partial condensation of steam, without allowing any seam to escape is known as steam

is the pressure difference, which is necessary to draw the required quantity of air for combustion and to remove the flue gases out of the system.

Thus the object of producing draught in a boiler is, To provide sufficient quantity of air for combustionTo make the resulting hot gases, to flow through the system.To discharge these gases to the atmosphere, through the chimney.

Usually this drought (pressure difference) in boiler is of small magnitude and is measured in mm of water column by means of draught gauge / manometer.

The amount of draught depends upon,

Nature and depth of fuel on the grate. Design of combustion chamber/firebox. Rate of combustion required. Resistance offered in the system due to baffles, tubes, Superheater, economiser, air pre-heater, etc.

Draught is broadly classified into 2-types, Natural or chimney draught

Fan Draught (Produced by Mechanical Fans)

Forced draught Induced draught


nce used to pump the feed water into the boiler drum. The

the feed pump fails due to any reasons, then steam injector, the use of steam.

the water resulting from partial condensation of steam, without allowing any seam to escape is known as steam

is the pressure difference, which is necessary to draw the required quantity of

To provide sufficient quantity of air for combustion make the resulting hot gases, to flow through the system.

To discharge these gases to the atmosphere, through the chimney. Usually this drought (pressure difference) in boiler is of small magnitude and is

gauge / manometer.

iii) Balanced draught

(b) Steam jet draught (Producei) Induced draughtii) Forced draught

1. Natural or chimney draught

In this case the amount of draught directly depends upon the produced due to the difference in density between chimney and a similar column of cold air out side the chimney.

Let us first consider the case when fires are not lighted.

Let, the atmospheric pressure at grate level be Pat an altitude H. The pressure Ppressure goes on decreasing.

Now let us consider the case when fires are lighted and the chimney is full of hot gases. Under these circumstances, the pressure P2 at the top and the pressure due to hot gas column ‘H’. But pressure Pthe sum of pressure P2 and the pressure due to similar cold column of air H

Since, Pcold air > phot gases

P2 + Pressure due to cold column H > P

Pressure at grate due to cold column >column H.

This difference is called static draughtair will rush to the combustion chamber, where combustion of air and fuel takes place and hot gases are generated. Then these hot gases because of draught,and finally they are exhausted to the atmosphere through the chimney.


Balanced draught Steam jet draught (Produced by steam jet),

Induced draught Forced draught

Natural or chimney draught: It is produced by means of chimney only.In this case the amount of draught directly depends upon the height of chimney. It is produced due to the difference in density between the column of hot gases in the chimney and a similar column of cold air out side the chimney.

Let us first consider the case when fires are not lighted.

Let, the atmospheric pressure at grate level be P1 and p2 be the atmospheric pressure pressure P2 is lower than the pressure P1, because with the altitude

pressure goes on decreasing.

Now let us consider the case when fires are lighted and the chimney is full of hot gases. Under these circumstances, the pressure at the base of the chimney is the sum of

at the top and the pressure due to hot gas column ‘H’. But pressure Pand the pressure due to similar cold column of air H

hot gases

+ Pressure due to cold column H > P2 + Pressure due to hot column H

Pressure at grate due to cold column > Pressure at the chimney base due to hot

static draught and because of this pressure difference, (draught) air will rush to the combustion chamber, where combustion of air and fuel takes place and

. Then these hot gases because of draught, flow through the system and finally they are exhausted to the atmosphere through the chimney.


It is produced by means of chimney only. height of chimney. It is

the column of hot gases in the

be the atmospheric pressure , because with the altitude

Now let us consider the case when fires are lighted and the chimney is full of hot pressure at the base of the chimney is the sum of

at the top and the pressure due to hot gas column ‘H’. But pressure P1 at grate is and the pressure due to similar cold column of air H

+ Pressure due to hot column H

Pressure at the chimney base due to hot

and because of this pressure difference, (draught) air will rush to the combustion chamber, where combustion of air and fuel takes place and

flow through the system

Advantages of natural draught

1) Easy to construct.2) No power is required for producing the draught.3) Long life of 4) No maintenance is required.

Disadvantages

1) Tall chimney is required.2) Poor efficiency.3) Decreases with increase in out side temperature.4) No flexibility to create more draught to take peak loads.

2. Artificial draught:

In bigger power plants,required. For producing this much draught, the chimney height has to be increased considerably, which is neither convenient nor economical. Also, since the draught depends upon the climatic conditionproducing the required draught and draught. (a) i) Forced draught

[Please see fig. on next page] In a Forced draught system, a Fan or Blower is provided as shown in fig. which

forces the air in the combustion chamber. In the combustion chamber combustion of air and fuel takes place and hot gases are generated. These gases are then flues, economiser, air pregases. This draught system is known positive draught system, since the pressure of gases throughout the system is above atmospheric pressure.

It is to be noted that, the function of chimney used is to discharge the gases high in the atmosphere to reduce air pollution and it is not much significant for producing draught.


Advantages of natural draught

Easy to construct. No power is required for producing the draught. Long life of chimney. No maintenance is required.

Tall chimney is required. Poor efficiency. Decreases with increase in out side temperature. No flexibility to create more draught to take peak loads.

In bigger power plants, the draught of the order of 25-350 mm of H2 O column is required. For producing this much draught, the chimney height has to be increased considerably, which is neither convenient nor economical. Also, since the draught depends upon the climatic conditions, some mechanical equipments are producing the required draught and the draughts so produced is called as the

i) Forced draught [Please see fig. on next page]

In a Forced draught system, a Fan or Blower is provided as shown in fig. which forces the air in the combustion chamber. In the combustion chamber combustion of air and fuel takes place and hot gases are generated. These gases are then forced to pass throflues, economiser, air pre-heater and then they are exhausted after recovering heat of flue

system is known positive draught system, since the pressure of gases system is above atmospheric pressure.



No flexibility to create more draught to take peak loads.

O column is required. For producing this much draught, the chimney height has to be increased considerably, which is neither convenient nor economical. Also, since the draught

s, some mechanical equipments are adopted for produced is called as the Artificial

In a Forced draught system, a Fan or Blower is provided as shown in fig. which forces the air in the combustion chamber. In the combustion chamber combustion of air and

forced to pass through the heater and then they are exhausted after recovering heat of flue

system is known positive draught system, since the pressure of gases


(a) ii) Induced Draught

In this system, the Blower or Induced Draught fan is located near the base of chimney. The air is sucked in the system, by reducing the pressure through the system below atmosphere. The flue gases, generated after combustion are and after recovering heat in the economiser, airchimney to the atmosphere.

Here it is to be noted that the draught produced is independent of the temperature of hot gases, to the gases may be discharged as cold as pas possible.

• Advantage of Forced Draught (F.D.) over Induced Draught (I.D.)1. The size and power 2. Since the I.D. fan handles hot gases, water cooled or

used. 3. F.D. fan consumers less power and normal bearing can be used.


ii) Induced Draught

In this system, the Blower or Induced Draught fan is located near the base of chimney. The air is sucked in the system, by reducing the pressure through the system below atmosphere. The flue gases, generated after combustion are drawn through the system

d after recovering heat in the economiser, air-preheater, they are exhausted through the chimney to the atmosphere.

Here it is to be noted that the draught produced is independent of the temperature of hot gases, to the gases may be discharged as cold as possible after recovering as much heat

Advantage of Forced Draught (F.D.) over Induced Draught (I.D.)The size and power required by I.D. fan is more because this fan handles more gases.Since the I.D. fan handles hot gases, water cooled or air cooled bearings are to be

F.D. fan consumers less power and normal bearing can be used.


In this system, the Blower or Induced Draught fan is located near the base of chimney. The air is sucked in the system, by reducing the pressure through the system

drawn through the system preheater, they are exhausted through the

Here it is to be noted that the draught produced is independent of the temperature of ossible after recovering as much heat

Advantage of Forced Draught (F.D.) over Induced Draught (I.D.) required by I.D. fan is more because this fan handles more gases.

air cooled bearings are to be

(a) iii) Balanced Draught

It is always preferable to use combination of I.D. and F.D. instead of Induced draught alone.


iii) Balanced Draught

It is always preferable to use combination of I.D. and F.D. instead of


It is always preferable to use combination of I.D. and F.D. instead of Forced or

Applied Thermodynamic notes

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