Introduction to Engineering ThermodynamicsPCB 1043LecturersDr. Khalik M. SabilExt: 7684Email: khalik_msabil@petronas.com.myRoom: 16-03-32

References:Text bookThermodynamics: An Engineering Approach (4 th edition)Yunus A. Cengel & Michael A. BolesSupplements:1) Fundamentals of Engineering Thermodynamics by Moran & Shapiro2) Fundamentals of Thermodynamics by Sonntag, Borgnakke & Van Wylen3) Engineering Thermodynamics by J.B. Jones

Course Outlines:

Chapter 1: Basics Concepts of ThermodynamicsChapter 2: Properties of Pure SubstancesChapter 3: Energy Transfer by Heat, Work and MassChapter 4: The First Law of Thermodynamics Chapter 5: The Second Law of ThermodynamicsChapter 6: EntropyChapter 7: Thermodynamic CyclesChapter 6: Introduction to phase equilibria

CHAPTER 1BASIC CONCEPTS OF THERMODYNAMICS

What is Thermodynamics?Early description: Convert heat into power

Current Definition: The study of energy and energy transformations, including power generation, refrigeration and relationship among the properties of matterGreek WordsTherme(heat)Dynamis(Power)

1.1 What is Energy?Ability to cause changesOne of the most fundamental laws of nature is the Conservation of energy principle - during an interaction, energy can change from one form to another but the total amount of energy remains constant. E.g. a rock falling off a cliff & in the diet industry.Laws of Thermodynamics:Zeroth Law = dealing with thermal equilibriumFirst Law = deal with conservation of energySecond Law = energy has quality as well as quantity, and actual processes occur in the direction of decreasing quality of energy.Hot heat Cold body, spontaneous Coldheat Hot body, requires work

Third Law =entropy of pure crystalline substance at absolute zero temperature is zero

Application Areas of Thermodynamics House-hold utensils appliances:Air-cond, heater, refrigeratorhumidifier, pressure cooker, water heatercomputer & TV

Engines:Automotive, aircraft, rocket

Plant/ FactoryRefinery, power plants, nuclear power plant

1.2 Dimensions and Units

DimensionPrimarySecondaryM - massL - lengthT - temperaturet - timen - moleA - AmpereEg: Volume V velocity v energy EUnitsSI - International System - Commonly appliedEnglish System - also known as United States CustomarySystem (USCS)

1.3Closed and Open SystemsThermodynamic system (system) - quantity of matter or a region in space chosen for study.Surroundings - the mass or region outside the system Boundary - the real or imaginary surface that separates the system from its surrounding - is the contact surface shared by both the system & surroundings - has zero thickness & can either contain any mass nor occupy volume in space. - can be fixed or movable

Boundaryfixedmovable

Types of system:(a) isolated - no heat/ mass transfer across boundary(b) closed(control mass) - only heat transferred(c) open system(control volume) - heat & mass transferred (b)(c)

1.4EnergyForms of energy - thermal, mechanical, chemical, kinetic, potential, electric, magnetic & nuclearE = total energy i.e sum of all energy in a systeme = total energy = E (kJ/kg)mass mForms of energy that make up the total energy of a system :

Energy formmacroscopicmicroscopicenergy of a system as a whole with respect to some outside reference frames, e.g. KE, PE- related to molecular structure of a system and the degree of molecular activity- independent of outside reference frames

Sum of all microscopic forms of energy = Internal Energy (U)Macroscopic forms of energy

Therefore, E = U + KE + PE (kJ)

Kinetic energy (KE)- result of motion relative to some reference frameKE = mv2/2 (kJ)

where v = velocity of the system relative to some fixed reference frame (m/s) m = mass of an object (kg)Potential energy (PE) - due to elevation in a gravitational fieldPE = mgh (kJ)

where g = gravitational acceleration, 9.81 m/s2 h = elevation of center of gravity of a system relative to some arbitrarily plane (m)

1.5Internal EnergyInternal energy - sum of all microscopic forms of energy of a systemrelated to - 1) molecular structure 2) degree of molecular activity

Latent heat - Internal energy associated to with the phase of a system - phase -change process can occur without a change in the chemical composition of a system

I. EKEPEmolecular translationmolecular rotationelectron translationmolecular vibrationelectron spinnuclear spina.k.a sensible energy

depend on the temperature

1.6Properties of a SystemProperty - any characteristic of a system or any quantity that describe a system

Some familiar properties are P, T, V and m. But can be extended to include less familiar ones such as viscosity, thermal conductivity, thermal expansion coefficient and etcDensity (mass per unit volume), (kg/m3) depends on T & P

Specific gravity or relative density (ratio of the density of a substance to the density of some standard substance at a specified temperature) e.g. for water,

Specific volume, (m3/kg)

Specific properties - extensive properties per unit massE.g. specific volume (v = V/m) and specific total energy (e = E/m)

PropertiesIntensiveExtensiveindependent of the size/extent of the systemdependent on the size/extent of the systemT, P, age, colourmVtotal E

1.7State & EquilibriumState a set of properties that describe the condition of a system at certain timeAt a given state, all the properties of a system have fixed values. If the value of one property changes, the state will change to a different one.Equilibrium statesteady state/ state of balance & no change in time

Thermal equilibriumT is the same throughout the system

Mechanical equilibriumP is the same throughout

Phase equilibriumm of each phase unchanged

Chemical equilibriumchemical composition unchanged

Thermal equilibrium(uniform temperature)

1.8Processes & CycleProcessany change that a system undergoes from one equilibrium state to another

PathSeries of states through which a system passes during a process

need to specify the initial & final states of the process, as well as the path it follows, and the interactions with the surroundings.

1.9Quasi-equilibrium/ Quasi-static

When a process proceeds in such a manner that the system remains infinitesimally close to equilibrium state at all times.Sufficiently slow process that allows the system to adjust to itself internally so that properties in one part of the system do not change any faster than those at other parts.

Slow compression(quasi-equilibrium)very fast compression(non-quasi equilibrium)

The prefix iso- is often used to designate a process for which a particular property remains constant.Isothermal Processa process when T remains constant

IsobaricP constant

Isochoric/ Isometricspecific volume v remains constant

A system is said to have undergone a cycle if it returns to its initial state at the end of the process.For a cycle, the initial & final states are identical

1.10PressureP == Unit = N/m2 or Pa Gas or liquidPressureSolidsStressCommon units 1 bar = 105 Pa 1 atm = 101,325 Pa = 1.01325 bars1 kgf/ cm2 = 0.9807 bar = 0.96788 atmEnglish unitIbf/in2 or psi

Absolute pressureActual pressure at at given position & measured relative to absolute vacuumGage pressureDifference between absolute pressure & local atmospheric pressureVacuum pressureDifference between atmospheric pressure & absolute pressure

Absolute, gage & vacuum pressures are all +ve quantities & related to each other by:Pgage = Pabs - Patm(for pressure above Patm)Pvac = Patm - Pabs(for pressure below Patm)

In thermo, absolute pressure is always used unless stated.

Example 1-1A vacuum gage connected to a chamber reads 5.8 psi at a location where the atmospheric pressure is 14.5 psi. Determine the absolute pressure in the chamber.

Using Pvac = Patm - Pabs = 14.5 - 5.8 = 8.7 psi

ManometerSmall to moderate pressure difference are measured by a manometer and a differential fluid column of height h corresponds to a pressure difference between the system and the surrounding of the manometer.

Other Pressure Measurement DeviceBourdon Tube

Modern pressure sensors:1) Pressure transducers2) Piezoelectric material

Example 1-2 A vacuum gage connected to a tank reads 30 kPa at a location where the atmospheric pressure is 98 kPa. What is the absolute pressure in the tank?Solution:Pabs = Patm - Pgage = 98 kPa - 30 kPa = 68 kPa Example 1-3A pressure gage connected to a valve stern of a truck tire reads 240 kPa at a location where the atmospheric pressure is 100 kPa. What is the absolute pressure in the tire, in kPa and in psia?Solution:Pabs = Patm - Pgage = 100 kPa + 240 kPa = 340 kPa

The pressure in psia isPabs = 340 kPa= 49.3 psia

What is the gage pressure of the air in the tire, in psig?Pgage = Pabs - Patm = 49.3 psia - 14.7 psia = 34.6 psigExample 1-4Both a gage and a manometer are attached to a gas tank to measure its pressure. If the pressure gage reads 80 kPa, determine the distance between the two fluid levels of the manometer if the fluids is mercury whose density is 13,600 kg/m3.

Temperature Measure of hotness and coldnessTransfer of heat from higher to lower temp. until both bodies attain the same temp. At that point, heat transfer stops and the two bodies have reached thermal equilibriumrequirement: equality of temperature

Zeroth Law of Thermodynamics:Two bodies are in thermal equilibrium when they have reached the same temperature. If two bodies are in thermal equilibrium with a third body, they are also in thermal equilibrium with each other.

Temperature scales:Celcius (C)Fahrenheit (F)Kelvin (K)Rankine (R)

Conversion:

T(K) = T(C) + 273.15

T(R) = T(F) + 459.67

T K = (T2C +273.15) - (T1C + 273.15) = T2C - T1C = TC

T R = TC

DT

Temperature Scale Comparison

Example 1:

Consider a system whose temperature is 18C. Express this temperature in R, K and F.

Example 2:The temperature of a system drops by 27 F during a cooling process. Express this drop in temperature in K, R & C

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