Thermodynamics: An Engineering Approach, 7 Edition
Thermodynamics: An Engineering Approach, 7th EditionYunus A. Cengel, Michael A. BolesMcGraw-Hill, 2011 Chapter 1INTRODUCTION ANDBASIC CONCEPTSMehmet KanogluCopyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Objectives Identify the unique vocabulary associated withthermodynamics through the precise definition ofbasic concepts to form a sound foundation for thedevelopment of the principles of thermodynamics. Review the metric SI and the English unit systems. Explain the basic concepts of thermodynamics suchas system, state, state postulate, equilibrium,process, and cycle. Review concepts of temperature, temperature scales,pressure, and absolute and gage pressure. Introduce an intuitive systematic problem-solvingtechnique.2
THERMODYNAMICS AND ENERGY Thermodynamics: The science ofenergy. Energy: The ability to cause changes. The name thermodynamics stems fromthe Greek words therme (heat) anddynamis (power). Conservation of energy principle:During an interaction, energy can changefrom one form to another but the totalamount of energy remains constant. Energy cannot be created or destroyed. The first law of thermodynamics: Anexpression of the conservation of energyprinciple. The first law asserts that energy is athermodynamic property.Energy cannot be createdor destroyed; it can onlychange forms (the first law).3
The second law of thermodynamics:It asserts that energy has quality aswell as quantity, and actual processesoccur in the direction of decreasingquality of energy. Classical thermodynamics: Amacroscopic approach to the study ofthermodynamics that does not requirea knowledge of the behavior ofindividual particles. It provides a direct and easy way to thesolution of engineering problems and itis used in this text. Statistical thermodynamics: Amicroscopic approach, based on theaverage behavior of large groups ofindividual particles. It is used in this text only in thesupporting role.Conservation of energyprinciple for the human body.Heat flows in the direction ofdecreasing temperature.4
Application Areas of Thermodynamics5
IMPORTANCE OF DIMENSIONS AND UNITS Any physical quantity can be characterized bydimensions. The magnitudes assigned to the dimensionsare called units. Some basic dimensions such as mass m,length L, time t, and temperature T areselected as primary or fundamentaldimensions, while others such as velocity V,energy E, and volume V are expressed interms of the primary dimensions and arecalled secondary dimensions, or deriveddimensions. Metric SI system: A simple and logicalsystem based on a decimal relationshipbetween the various units. English system: It has no apparentsystematic numerical base, and various unitsin this system are related to each other ratherarbitrarily.6
Some SI and English UnitsWork Force Distance1 J 1 N·m1 cal 4.1868 J1 Btu 1.0551 kJThe SI unit prefixes are used in allbranches of engineering.The definition of the force units.7
W weightm massg gravitationalaccelerationA body weighing60 kgf on earthwill weigh only 10kgf on the moon.The relative magnitudes of the forceunits newton (N), kilogram-force(kgf), and pound-force (lbf).The weight of a unitmass at sea level.8
Dimensional homogeneityAll equations must be dimensionally homogeneous.Unity Conversion RatiosAll nonprimary units (secondary units) can beformed by combinations of primary units.Force units, for example, can be expressed asThey can also be expressed more convenientlyas unity conversion ratios asUnity conversion ratios are identically equal to 1 andare unitless, and thus such ratios (or their inverses)can be inserted conveniently into any calculation toproperly convert units.To be dimensionallyhomogeneous, all theterms in an equationmust have the same unit.9
SYSTEMS AND CONTROL VOLUMES System: A quantity of matter or a regionin space chosen for study.Surroundings: The mass or regionoutside the systemBoundary: The real or imaginary surfacethat separates the system from itssurroundings.The boundary of a system can be fixed ormovable.Systems may be considered to be closedor open.Closed system(Control mass):A fixed amountof mass, and nomass can crossits boundary.10
An open system (acontrol volume) with oneinlet and one exit.Open system (control volume): A properlyselected region in space.It usually encloses a device that involvesmass flow such as a compressor, turbine, ornozzle.Both mass and energy can cross theboundary of a control volume.Control surface: The boundaries of a controlvolume. It can be real or imaginary.11
PROPERTIESOF A SYSTEM Property: Any characteristic of asystem.Some familiar properties arepressure P, temperature T, volumeV, and mass m.Properties are considered to beeither intensive or extensive.Intensive properties: Those thatare independent of the mass of asystem, such as temperature,pressure, and density.Extensive properties: Thosewhose values depend on the size—or extent—of the system.Criterion to differentiate intensiveSpecific properties: Extensiveand extensive properties.properties per unit mass.12
Continuum Matter is made up of atoms that arewidely spaced in the gas phase. Yetit is very convenient to disregard theatomic nature of a substance andview it as a continuous,homogeneous matter with no holes,that is, a continuum.The continuum idealization allows usto treat properties as point functionsand to assume the properties varycontinually in space with no jumpdiscontinuities.This idealization is valid as long asthe size of the system we deal withis large relative to the spacebetween the molecules.This is the case in practically allproblems.In this text we will limit ourconsideration to substances that canbe modeled as a continuum.Despite the large gaps betweenmolecules, a substance can be treated asa continuum because of the very largenumber of molecules even in anextremely small volume.13
DENSITY AND SPECIFIC GRAVITYDensitySpecific volumeSpecific gravity: The ratioof the density of asubstance to the density ofsome standard substanceat a specified temperature(usually water at 4 C).Specific weight: Theweight of a unit volumeof a substance.Density ismass per unitvolume;specific volumeis volume perunit mass.14
STATE AND EQUILIBRIUM Thermodynamics deals withequilibrium states.Equilibrium: A state of balance.In an equilibrium state there are nounbalanced potentials (or drivingforces) within the system.Thermal equilibrium: If thetemperature is the same throughoutthe entire system.Mechanical equilibrium: If there isno change in pressure at any pointof the system with time.Phase equilibrium: If a systeminvolves two phases and when themass of each phase reaches anequilibrium level and stays there.Chemical equilibrium: If thechemical composition of a systemdoes not change with time, that is,no chemical reactions occur.A system at two different states.A closed system reaching thermalequilibrium.15
The State Postulate The number of propertiesrequired to fix the state of asystem is given by the statepostulate: The state of a simplecompressible system iscompletely specified bytwo independent,intensive properties. Simple compressiblesystem: If a system involvesno electrical, magnetic,gravitational, motion, andsurface tension effects.The state of nitrogen isfixed by two independent,intensive properties.16
PROCESSES AND CYCLESProcess: Any change that a system undergoes from one equilibrium state toanother.Path: The series of states through which a system passes during a process.To describe a process completely, one should specify the initial and final states,as well as the path it follows, and the interactions with the surroundings.Quasistatic or quasi-equilibrium process: When a process proceeds in sucha manner that the system remains infinitesimally close to an equilibrium stateat all times.17
Process diagrams plotted byemploying thermodynamic propertiesas coordinates are very useful invisualizing the processes.Some common properties that areused as coordinates are temperatureT, pressure P, and volume V (orspecific volume v).The prefix iso- is often used todesignate a process for which aparticularproperty remains constant.Isothermal process: A processduring which the temperature Tremains constant.Isobaric process: A process duringwhich the pressure P remainsconstant.Isochoric (or isometric) process: Aprocess during which the specificvolume v remains constant.Cycle: A process during which theinitial and final states are identical.The P-V diagram of a compressionprocess.18
The Steady-Flow Process The term steady implies nochange with time. Theopposite of steady isunsteady, or transient.A large number ofengineering devices operatefor long periods of timeunder the same conditions,and they are classified assteady-flow devices.Steady-flow process: Aprocess during which a fluidflows through a controlvolume steadily.Steady-flow conditions canbe closely approximated bydevices that are intended forcontinuous operation suchas turbines, pumps, boilers,condensers, and heatexchangers or power plantsor refrigeration systems.During a steadyflow process, fluidproperties withinthe controlvolume maychange withposition but notwith time.Under steady-flow conditions, the massand energy contents of a control volumeremain constant.19
TEMPERATURE AND THE ZEROTH LAW OFTHERMODYNAMICS The zeroth law of thermodynamics: If two bodies are in thermalequilibrium with a third body, they are also in thermal equilibrium witheach other.By replacing the third body with a thermometer, the zeroth law canbe restated as two bodies are in thermal equilibrium if both have thesame temperature reading even if they are not in contact.Two bodies reachingthermal equilibriumafter being broughtinto contact in anisolated enclosure.20
Temperature Scales P versus T plotsAll temperature scales are based onof thesome easily reproducible states such asexperimentalthe freezing and boiling points of water:the ice point and the steam point.data obtainedfrom a constantIce point: A mixture of ice and watervolume gasthat is in equilibrium with air saturatedwith vapor at 1 atm pressure (0 C orthermometer32 F).using fourdifferent gasesSteam point: A mixture of liquid waterand water vapor (with no air) inat different (butequilibrium at 1 atm pressure (100 C or low) pressures.212 F).Celsius scale: in SI unit systemFahrenheit scale: in English unitsystemThermodynamic temperature scale: Atemperature scale that is independent ofthe properties of any substance.Kelvin scale (SI) Rankine scale (E)A temperature scale nearly identical tothe Kelvin scale is the ideal-gastemperature scale. The temperatureson this scale are measured using aA constant-volume gas thermometer wouldconstant-volume gas thermometer.21read 273.15 C at absolute zero pressure.
Comparison oftemperaturescales.Comparison ofmagnitudes ofvarioustemperatureunits. The reference temperature in the original Kelvin scale was the ice point,273.15 K, which is the temperature at which water freezes (or ice melts).The reference point was changed to a much more precisely reproduciblepoint, the triple point of water (the state at which all three phases of watercoexist in equilibrium), which is assigned the value 273.16 K.22
PRESSUREPressure: A normal force exertedby a fluid per unit area68 kg136 kgAf eet 300cm20.23 kgf/cm20.46 kgf/cm2P 68/300 0.23 kgf/cm2The normal stress (or “pressure”) on thefeet of a chubby person is much greaterthan on the feet of a slim person.Somebasicpressuregages.23
Absolute pressure: The actual pressure at a given position. It ismeasured relative to absolute vacuum (i.e., absolute zero pressure). Gage pressure: The difference between the absolute pressure andthe local atmospheric pressure. Most pressure-measuring devices arecalibrated to read zero in the atmosphere, and so they indicate gagepressure. Vacuum pressures: Pressures below atmospheric pressure. Throughoutthis text, thepressure Pwill denoteabsolutepressureunlessspecifiedotherwise.24
Variation of Pressure with DepthWhen the variation of densitywith elevation is knownThe pressure of a fluid at restincreases with depth (as aresult of added weight).Free-body diagram of a rectangularfluid element in equilibrium.25
In a room filled witha gas, the variationof pressure withheight is negligible.Pressure in a liquidat rest increaseslinearly withdistance from thefree surface.The pressure is thesame at all points ona horizontal plane ina given fluidregardless ofgeometry, providedthat the points areinterconnected bythe same fluid.26
Pascal’s law: The pressure applied to aconfined fluid increases the pressurethroughout by the same amount.The area ratio A2/A1 iscalled the ideal mechanicaladvantage of the hydrauliclift.Lifting of a large weightby a small force by theapplication of Pascal’slaw.27
The ManometerIt is commonly used to measure small andmoderate pressure differences. A manometercontains one or more fluids such as mercury, water,alcohol, or oil.Measuring thepressure drop acrossa flow section or a flowdevice by a differentialmanometer.The basicmanometer.In stacked-up fluid layers, thepressure change across a fluid layerof density ρ and height h is ρgh.28
Other Pressure Measurement Devices Bourdon tube: Consists of a hollow metal tubebent like a hook whose end is closed andconnected to a dial indicator needle. Pressure transducers: Use various techniquesto convert the pressure effect to an electricaleffect such as a change in voltage, resistance,or capacitance. Pressure transducers are smaller and faster,and they can be more sensitive, reliable, andprecise than their mechanical counterparts. Strain-gage pressure transducers: Work byhaving a diaphragm deflect between twochambers open to the pressure inputs. Piezoelectric transducers: Also called solidstate pressure transducers, work on theprinciple that an electric potential is generated ina crystalline substance when it is subjected tomechanical pressure.Various types of Bourdon tubes usedto measure pressure.29
THE BAROMETER AND ATMOSPHERIC PRESSURE Atmospheric pressure is measured by a device called a barometer; thus, theatmospheric pressure is often referred to as the barometric pressure. A frequently used pressure unit is the standard atmosphere, which is defined asthe pressure produced by a column of mercury 760 mm in height at 0 C (ρHg 13,595 kg/m3) under standard gravitational acceleration (g 9.807 m/s2).The length or thecross-sectional areaof the tube has noeffect on the heightof the fluid column ofa barometer,provided that thetube diameter islarge enough toavoid surface tension(capillary) effects.The basic barometer.30
PROBLEM-SOLVING TECHNIQUE Step 1: Problem Statement Step 2: Schematic Step 3: Assumptions and Approximations Step 4: Physical Laws Step 5: Properties Step 6: Calculations Step 7: Reasoning, Verification, and DiscussionEES (Engineering Equation Solver) (Pronounced as ease):EES is a program that solves systems of linear or nonlinearalgebraic or differential equations numerically. It has a largelibrary of built-in thermodynamic property functions as well asmathematical functions. Unlike some software packages, EESdoes not solve engineering problems; it only solves the equationssupplied by the user.31
Summary Thermodynamics and energy Application areas of thermodynamics Importance of dimensions and units Some SI and English units, Dimensional homogeneity,Unity conversion ratios Systems and control volumesProperties of a systemDensity and specific gravityState and equilibrium The state postulate Processes and cycles The steady-flow process Temperature and the zeroth law of thermodynamics Temperature scales Pressure Variation of pressure with depth The manometer and the atmospheric pressureProblem solving technique32
thermodynamics through the precise definition of basic concepts to form a sound foundation for the development of the principles of thermodynamics. Review the metric SI and the English unit systems. Explain the basic concepts of thermodynamics such as system, state, state postulate, equilibrium, process, and cycle.
1.4 Second Law of Thermodynamics 1.5 Ideal Gas Readings: M.J. Moran and H.N. Shapiro, Fundamentals of Engineering Thermodynamics,3rd ed., John Wiley & Sons, Inc., or Other thermodynamics texts 1.1 Introduction 1.1.1 Thermodynamics Thermodynamics is the science devoted to the study of energy, its transformations, and its
Thermodynamics an Engineering Approach by Yunus Cengel and Boles . Engineering Thermodynamics by Achuthan second edition. Thermal Science and Engineering Dr D.S.Kumar Thermodynamics is a science that deals with all aspects of energy conversion, energy exchange and energy
Reversible and Irreversible processes First law of Thermodynamics Second law of Thermodynamics Entropy Thermodynamic Potential Third Law of Thermodynamics Phase diagram 84/120 Equivalent second law of thermodynamics W Q 1 1 for any heat engine. Heat cannot completely be converted to mechanical work. Second Law can be formulated as: (A .
Engineering Fundamentals-Thermodynamics By Professor Paul A. Erickson . Basic Thermodynamics . Systems Engineering: Thermodynamics, Fluid Mechanics, and Heat Transfer Michael J. Moran Howard N. Shapiro Bruce R. Munson David P. DeWitt John Wiley & Sons, Inc.
Thermodynamics : an interactive approach : a text based on webware / Subrata (Sooby) Bhattacharjee, San Diego State University. — First edition. pages cm ISBN-13: 978--13-035117-3 ISBN-10: -13-035117-2 1. Thermodynamics—Textbooks.2. Machinery, Dynamics of—Textbooks. 3. Thermodynamics—Computer-assisted instruction. I. Title. TJ265.B58 2014
Engg. Mathematics 2. Engg. Physics/chemistry Unit: I Laws of thermodynamics 10 Hrs. Introduction of thermodynamics, Review of basic definitions, Thermodynamic properties and their units, Zeroth law of thermodynamics, Macro and Microscopic Approach, First law of thermodynamics, Joules
1. Fundamentals of Engineering Thermodynamics, 8th ed., by Moran, Shapiro, et al., John Wiley and Sons, 2014 (ISBN 9781118412930) 2. Thermodynamics for Engineers (Schaum's Outlines) 3rd Edition by Merle Potter 3. DOE Fundamentals Handbook Thermodynamics, Heat Transfer and Fluid Flow,Volume 1 of 3, DOE-HDBK-1012/3 -92 Optional References TBD
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