Prof. R. Shanthini Dec 10, 2011
1
Module 01
Energy Basics
Energy
Power
Forms of energy
Thermodynamic laws
Entropy
Exergy
Combustion fundamentals
Prof. R. Shanthini Dec 10, 2011
2
A few suggested references
Shanthini, R., 2009. Thermodynamics for beginners.
Peradeniya: Science Education Unit.
Certain chapters available from:
http://www.rshanthini.com/ThermoBook.htm
MacKay, D.J.C., 2009. Sustainable energy: without
the hot air. Cambridge: UIT Cambridge Ltd.
Available from:
http://www.withouthotair.com/download.html
Prof. R. Shanthini Dec 10, 2011
3
• What is energy?
– energy is the ability to do work (defined loosely)
Energy is not a ‘thing’ or ‘substance’.
Energy cannot be seen, heard or felt.
Energy is a concept.
Prof. R. Shanthini Dec 10, 2011
4
• What is energy?
– energy is the ability to do work (defined loosely)
• What is work?
– force exerted over a distance (scientific definition)
FF is the force pushing the ball
Prof. R. Shanthini Dec 10, 2011
5
• What is energy?
– energy is the ability to do work (defined loosely)
• What is work?
– force exerted over a distance (scientific definition)
F
D
Work = F x D
D is the distance over which the ball is moved
F is the force pushing the ball
Prof. R. Shanthini Dec 10, 2011
6
• What is energy?
– energy is the ability to do work (defined loosely)
• What is power?
– power is the rate at which work is done
Work = Force x Distance
Power = Work / Time
Prof. R. Shanthini Dec 10, 2011
7
• What is the unit of Energy?
• What is the unit of Work?
• What is the unit of Power?
Prof. R. Shanthini Dec 10, 2011
8
Units for energy / work
joule in SI-system
1 J (joule) = 1 N·m = 1 (N/m2) ·m3 = 1 Pa·m3
1 N (newton) = 1 (kg.m/s2) is the unit of force
1 Pa (pascal) = 1 N/m2 is the unit for pressure
Prof. R. Shanthini Dec 10, 2011
9
Submultiples Multiples
Value Symbol Name Value Symbol Name
10−1 J dJ decijoule 101 J daJ decajoule
10−2 J cJ centijoule 102 J hJ hectojoule
10−3 J mJ millijoule 103 J kJ kilojoule
10−6 J µJ microjoule 106 J MJ megajoule
10−9 J nJ nanojoule 109 J GJ gigajoule
10−12 J pJ picojoule 1012 J TJ terajoule
10−15 J fJ femtojoule 1015 J PJ petajoule
10−18 J aJ attojoule 1018 J EJ exajoule
10−21 J zJ zeptojoule 1021 J ZJ zettajoule
10−24 J yJ yoctojoule 1024 J YJ yottajoule
SI multiples for joules (W)
http://en.wikipedia.org/wiki/Orders_of_magnitude_(energy)
Prof. R. Shanthini Dec 10, 2011
10
Units for power
watt in SI-system
1 W (watt) = 1 J/s = 1 N.m/s
60 W = 60 J/s
= 60*60 J/m
= 60*60*60 J/h
= 216,000 J/h
= 216 kJ/h
Prof. R. Shanthini Dec 10, 2011
11
Submultiples Multiples
Value Symbol Name Value Symbol Name
10−1 W dW deciwatt 101 W daW decawatt
10−2 W cW centiwatt 102 W hW hectowatt
10−3 W mW milliwatt 103 W kW kilowatt
10−6 W µW microwatt 106 W MW megawatt
10−9 W nW nanowatt 109 W GW gigawatt
10−12 W pW picowatt 1012 W TW terawatt
10−15 W fW femtowatt 1015 W PW petawatt
10−18 W aW attowatt 1018 W EW exawatt
10−21 W zW zeptowatt 1021 W ZW zettawatt
10−24 W yW yoctowatt 1024 W YW yottawatt
SI multiples for watts (J)
Prof. R. Shanthini Dec 10, 2011
12
Global Energy Consumption
http://en.wikipedia.org/wiki/Orders_of_magnitude_(energy)
Global Consumption = 15 TW = 15x1012 W
= 250,000,000,000 of 60 W bulbs
= about 35 of 60 W bulbs per person
Prof. R. Shanthini Dec 10, 2011
13
Global Energy Consumption
http://en.wikipedia.org/wiki/Orders_of_magnitude_(energy)
Global Consumption = 15 TW = 15x1012 W
= 250,000,000,000 of 60 W bulbs
= about 35 of 60 W bulbs per person
Prof. R. Shanthini Dec 10, 2011
14
http://en.wikipedia.org/wiki/Orders_of_magnitude_(energy)
Global Consumption = 15 TW = 15x1012 J/s = 54x1015 J/h
Global Energy Consumption
Prof. R. Shanthini Dec 10, 2011
15
One joule in everyday life is approximately:
The energy required to raise the temperature of cool, dry air by one degree Celsius.
A person at rest releases 100 joules of heat every second.
Prof. R. Shanthini Dec 10, 2011
16
• What is energy?– energy is the ability to do work (defined loosely)
• What is work?– force exerted over a distance (scientific definition)
• Is heat energy too?– heat is a form of energy that flows from a warmer object to a cooler object
– work sometimes gets converted to heat (think of examples)
– heat sometimes gets converted to work (think of examples)
Prof. R. Shanthini Dec 10, 2011
17
Units for heat
Joule / Calorie
1 calorie
= the energy needed to raise the temperature of 1 gram of water by 1oC
= 4.184 J (joules)
= 0.003 964 BTU (British thermal units)
Prof. R. Shanthini Dec 10, 2011
18
http://www.aps.org/policy/reports/popa-reports/energy/units.cfm
For more on energy units and conversions,
Visit
The American Physical Society Site
Prof. R. Shanthini Dec 10, 2011
19
• Kinetic Energy: • Potential Energy:• Thermal (or Heat) Energy:• Chemical Energy:• Electrical Energy:• Electrochemical Energy: • Sound Energy: • Electromagnetic Energy (light):• Nuclear Energy:
Basic Forms of Energy
Prof. R. Shanthini Dec 10, 2011
20
• Thermal (or Heat) Energy:
– Consider a hot cup of coffee. The coffee is said to possess "thermal energy", or "heat energy," which is really the collective, microscopic, kinetic, and potential energy of the molecules in the coffee.
• Chemical Energy:– Consider the ability of your body to do work. The glucose
(blood sugar) in your body is said to have "chemical energy" because the glucose releases energy when chemically reacted (combusted) with oxygen.
Source: http://euclidstube.com/poe/Thermodynamics.ppt
Basic Forms of Energy (continued)
Prof. R. Shanthini Dec 10, 2011
21
• Electrical Energy:
– All matter is made up of atoms, and atoms are made up of smaller particles, called protons, neutrons, and electrons. Electrons orbit around the center, or nucleus, of atoms, just like the moon orbits the earth. The nucleus is made up of neutrons and protons.
– Material, like metals, have certain electrons that are only loosely attached to their atoms. They can easily be made to move from one atom to another if an electric field is applied to them. When those electrons move among the atoms of matter, a current of electricity is created.
Source: http://euclidstube.com/poe/Thermodynamics.ppt
Basic Forms of Energy (continued)
Prof. R. Shanthini Dec 10, 2011
22
• Electrochemical Energy:
– Consider the energy stored in a battery. Like the example above involving blood sugar, the battery also stores energy in a chemical way. But electricity is also involved, so we say that the battery stores energy "electro-chemically". Another electron chemical device is a "fuel-cell".
Source: http://euclidstube.com/poe/Thermodynamics.ppt
Basic Forms of Energy (continued)
Prof. R. Shanthini Dec 10, 2011
23
• Sound Energy:
– Sound waves are compression waves associated with the potential and kinetic energy of air molecules. When an object moves quickly, for example the head of drum, it compresses the air nearby, giving that air potential energy. That air then expands, transforming the potential energy into kinetic energy (moving air). The moving air then pushes on and compresses other air, and so on down the chain.
Source: http://euclidstube.com/poe/Thermodynamics.ppt
Basic Forms of Energy (continued)
Prof. R. Shanthini Dec 10, 2011
24
Source: http://euclidstube.com/poe/Thermodynamics.ppt
• Electromagnetic Energy (light):
– Consider the energy transmitted to the Earth from the Sun by light (or by any source of light). Light, which is also called "electro-magnetic radiation". Why the fancy term? Because light really can be thought of as oscillating, coupled electric and magnetic fields that travel freely through space (without there having to be charged particles of some kind around).
– It turns out that light may also be thought of as little packets of energy called photons (that is, as particles, instead of waves). The word "photon" derives from the word "photo", which means "light".
Basic Forms of Energy (continued)
Prof. R. Shanthini Dec 10, 2011
25
Basic Forms of Energy (continued)
• Nuclear Energy:
– The Sun, nuclear reactors, and the interior of the Earth, all have "nuclear reactions" as the source of their energy, that is, reactions that involve changes in the structure of the nuclei of atoms.
Source: http://euclidstube.com/poe/Thermodynamics.ppt
Prof. R. Shanthini Dec 10, 2011
26
Energy is available in different forms.
Energy cannot be created or destroyed (which is a natural law).
Energy can change from one form to the other.
Prof. R. Shanthini Dec 10, 2011
27
The study of conversion of energy is known as
Thermodynamics.
Mostly, it is study of the connection between heat and work, and the conversion of one into the other.
Engineering examples: ……………………………………
Prof. R. Shanthini Dec 10, 2011
28
Thermodynamicsis based on fundamentals laws,
which are the natural laws.
These laws have not been proven wrong so far.
These laws will remain as fundamental laws until someone finds out that they are wrong.
If that happens then we need to redo all thermodynamics that has been developed so far.
Prof. R. Shanthini Dec 10, 2011
29
First Law of Thermodynamics
Energy is conserved.
That means, energy cannot be created or destroyed.
However, energy can change from one form to the other.
Prof. R. Shanthini Dec 10, 2011
30
Qin Wout
First Law of Thermodynamics
Heat energy that entered the system
Work energy that left the system
System
Energy of the system
E
Prof. R. Shanthini Dec 10, 2011
31
Qin Wout
Efinal - Einitial = Qin – Wout
ΔE = Qin – Wout
First Law of Thermodynamics
E
Prof. R. Shanthini Dec 10, 2011
32
First Law of Thermodynamics
First law is about the balance of quantities of energy.
It helps to keep account of what happen to all forms of energy that are involved in a process.
Prof. R. Shanthini Dec 10, 2011
33
Hot reservoir at TH K
Wout
Qin
Heat Engine
Apply First law to Heat Engine
Cold reservoir at TC K
Qout
A heat engine is a mechanical system.As it cycles through a repetitive motion, transfers heat from a high temperature heat bath to a low temperature bath, and performs work on its environment.
Example: Diesel cycle auto.howstuffworks.com/diesel.htm
Prof. R. Shanthini Dec 10, 2011
34
Hot reservoir at TH K
Wout
Qin
Heat Engine
Apply First law to Heat Engine
Cold reservoir at TC K
Qout
Qin = Wout + Qout
First law gives the following relationship:
Prof. R. Shanthini Dec 10, 2011
35
Hot reservoir at TH K
Wout
Qin
Heat Engine
We like to have an engine that converts all heat into work. That is, we would like to have
Is it possible?
Qin = Wout
Prof. R. Shanthini Dec 10, 2011
36
Qout
Hot reservoir at TH K
Wout
Qin
Heat Engine
Second law of thermodynamics says it is not possible to convert all heat into work in an engine.
It says it is necessary to throw away some heat to the environment.
Second Law of Thermodynamics
WHY?
Prof. R. Shanthini Dec 10, 2011
37
Hot reservoir at TH K
Wout
Qin
Heat Engine
Second Law of Thermodynamics
Cold reservoir at TC K
Qout
ηCarnot
= TC
1 - TH
Maximum possible thermal efficiency of the heat engine is
< 1ηCarnot
Since TC can never be zero,
Prof. R. Shanthini Dec 10, 2011
38
Hot reservoir at TH K
Wout
Qin
Heat Engine
Second Law of Thermodynamics
Cold reservoir at TC K
Qout
ηth = Wout
Qin
< ηth ηCarnot
< 1
Thermal efficiency of the heat engine is
Prof. R. Shanthini Dec 10, 2011
39
Hot reservoir at TH K
Wout
Qin
Heat Engine
Second Law of Thermodynamics
Cold reservoir at TC K
Qout
Qout ≠ 0
ηth = Wout
Qin
Thermal efficiency of the heat engine is
< 1
Qin ≠ Wout
Some heat is thrown away.
Prof. R. Shanthini Dec 10, 2011
40
EntropyWhen heat is transformed into work, as in the heat engines,
some heat is always lost to the environment (according to the Second Law).
This irrevocable loss of some energy to the environment is associated with an increase of disorder in that system.
Entropy acts as a function of the state of a system - where a high amount of entropy translates to higher chaos within the system, and low entropy signals a highly ordered state.
The Second Law tells that the quality of energy is degraded every time energy is used in any process. This ‘energy quality’ has been named exergy.
Prof. R. Shanthini Dec 10, 2011
41
ExergyThe Second Law tells us that the quality of a particular amount
of energy diminishes for each time this energy is used.
This means that the quality of energy in the universe as a whole is constantly diminishing.
All real processes are irreversible, since the quality of the energy driving them is lowered for all times.
Prof. R. Shanthini Dec 10, 2011
42
ExergyThe Second Law tells us about the direction of the universe
and all processes, namely towards a decreasing exergy content of the universe.
Processes that follow this general principle will be preferred.
The usable energy in a system is called exergy, and can be measured as the total of the free energies in the system. Unlike energy, exergy can be consumed.
Prof. R. Shanthini Dec 10, 2011
43
The energy of the universe is constant (First Law). Exergy is constantly consumed (Second Law).
In the end (very long time from now), exergy is used up in the universe, and no processes can run.
The entropy of a system increases whenever exergy is lost.
Prof. R. Shanthini Dec 10, 2011
44
Zeroth Law of Thermodynamics
If object A is in thermal equilibrium with object C,and object B is in thermal equilibrium with object C,then object A & B are also in thermal equilibrium.
Thermal Equilibrium = Same temperature
Thermal Equilibrium = No heat flow
Prof. R. Shanthini Dec 10, 2011
45
Third Law of Thermodynamics
It is impossible to reach absolute zero in a finite number of steps.
Prof. R. Shanthini Dec 10, 2011
46
Combustion is a process in which oxidizable materials such as fossil fuels are oxidized by use of oxygen (present in the air).
During this process energy is released in the form of heat.
Major combustion product is the global pollutant, carbon dioxide (CO2), which is a greenhouse gases.
Combustion products also include other local pollutants.
Combustion fundamentals include the nature of the fuels being burned, the nature of the products formed and the stoichiometry of the combustion reaction.
Combustion Fundamentals
Prof. R. Shanthini Dec 10, 2011
47
Combustion (or Fire) Triangle
Prof. R. Shanthini Dec 10, 2011
48
Combustion Engine
The combustion engine is used to power nearly all land vehicles and many water-based and air-based vehicles.
In an internal combustion engine, a fuel (gasoline for example) fills a chamber, then it is compressed to heat it up, and then is ignited by a spark plug, causing a small explosion which generates work.
Prof. R. Shanthini Dec 10, 2011
49
Combustion Engine
Prof. R. Shanthini Dec 10, 2011
50
Combustion Engine
Prof. R. Shanthini Dec 10, 2011
51
Combustion Engine
http://bancroft.berkeley.edu/Exhibits/physics/images/origins18.jpg
Prof. R. Shanthini Dec 10, 2011
52
Combustion Engine
http://images.yourdictionary.com/images/main/A4gastrb.jpg
Prof. R. Shanthini Dec 10, 2011
53
Stoichiometric (or theoretical) combustion is the ideal combustion process where fuel is burned completely.
A complete combustion is a process burning
- all the carbon (C) to (CO2),
- all the hydrogen (H) to (H2O) and
- all the sulphur (S) to (SO2).
With unburned components in the exhaust gas, such as C, H2, CO, the combustion process is incomplete and not stoichiometric.
http://www.engineeringtoolbox.com/stoichiometric-combustion-d_399.html
Combustion Fundamentals
Prof. R. Shanthini Dec 10, 2011
54
If an insufficient amount of air is supplied to the burner, unburned fuel, soot, smoke, and carbon monoxide exhausts from the boiler - resulting in heat transfer surface fouling, pollution, lower combustion efficiency, flame instability and a potential for explosion.
To avoid inefficient and unsafe conditions boilers normally operate at an excess air level.
http://www.engineeringtoolbox.com/stoichiometric-combustion-d_399.html
Combustion Fundamentals
Prof. R. Shanthini Dec 10, 2011
55
if air content is higher than the stoichiometric ratio - the mixture is said to be fuel-lean
if air content is less than the stoichiometric ratio - the mixture is fuel-rich
http://www.engineeringtoolbox.com/stoichiometric-combustion-d_399.html
Combustion Fundamentals
Prof. R. Shanthini Dec 10, 2011
56
Example - Stoichiometric Combustion of Methane - CH4
CH4 + 2 (O2 + 3.76 N2) -> CO2 + 2 H2O + 7.52 N2
If more air is supplied some of the air will not be involved in the reaction. The additional air is termed excess air, but the term theoretical air may also be used. 200% theoretical air is 100% excess air.
The chemical equation for methane burned with 25% excess air can be expressed asCH4 + 1.25 x 2 (O2 + 3.76 N2) -> CO2 + 2 H2O + 0.5 O2 + 9.4 N2
http://www.engineeringtoolbox.com/stoichiometric-combustion-d_399.html
Combustion Fundamentals
Prof. R. Shanthini Dec 10, 2011
57
Combustion Fundamentals
Excess Air and O2 and CO2 in Flue Gas
Approximate values for CO2 and O2 in the flue gas as result of
excess air (for various fuels) are estimated in the table below:
Excess Air%
Carbon Dioxide - CO2 - in Flue Gas (% volume)Oxygen in Flue Gas for all fuels (% volume)
Natural Gas
Propane Butane
Fuel OilBituminous Coal
Anthracite Coal
0 12 14 15.5 18 20 0
20 10.5 12 13.5 15.5 16.5 3
40 9 10 12 13.5 14 5
60 8 9 10 12 12.5 7.5
80 7 8 9 11 11.5 9
100 6 6 8 9.5 10 10
http://www.engineeringtoolbox.com/stoichiometric-combustion-d_399.html
Top Related