Chap.3 SummaryAsinglechemicalelementorcompoundAsubstancethat hasPure substanceHomogeneousmixtureofvariouschemicalelementsorcompoundsafixedchemicalcompositionmixtureoftwoormorephasesapuresubstanceCompressed liguid orsubcooled liquidliquidSaturated liquidSatruated liquid-vapor mixturePhase changeprocessSatruated vaporvaporSuperheatedvapor+Psat,Tsat,Latentheatoffusion/vaporization,sublimationsolidCritical pointSaturated liquid/vapor lineSuperheatedvaporregionT-v,P-v,P-T, P-v-T diagramsTripple pointCompressedliquid regionSaturated liquid-vaporregion1Enthalpy/焰:acombinationpropertyh=u+Pv(kJ/kg);Entropy/PropertiestablesSaturated liguid/vaporormixture.ht,ha,haQuality x=[0,1]SuperheatedvaporCompressedliquid P,TReferencestatevalues1PV=RTPV=mRTR,RuIdeal gasequationofstateIdeal-gas/realgasZ=Pv/RTCompressibilityfactorReducedPReducedTequationofstateGeneralizedVanderwallsPrincipleofcorresponding statescompressibility chartequationofstate
Chap.3 Summary 1 A substance that has a fixed chemical composition Phase change process A single chemical element or compound Enthalpy/焓: a combination property h=u+Pv (kJ/kg); Entropy/熵 Critical point T-v, P-v,P-T, P-v-T diagrams Properties tables Ideal-gas / real gas equation of state Pure substance liquid vapor solid Homogeneous mixture of various chemical elements or compounds mixture of two or more phases a pure substance Saturated liquid Satruated liquid-vapor mixture Satruated vapor Superheated vapor Compressed liquid or subcooled liquid Psat, Tsat, Latent heat of fusion/vaporization, sublimation Tripple point Saturated liquid/vapor line Superheated vapor region Compressed liquid region Saturated liquid-vapor region Saturated liquid/vapor or mixture. hf ,hg,hfg Quality x=[0,1] Superheated vapor Compressed liquid P, T Reference state/values Ideal gas equation of state Pv=RT PV=mRT R, Ru Compressibility factor Z=Pv/RT Reduced P Reduced T Principle of corresponding states Generalized compressibility chart Van der walls equation of state
Chap4 SummaryGeneral:Ow,=Pdy,P-VdiagramThework associatedBoundary workwithexpansionandIsobaricprocess,Pvn=const PolytropicprocesscompressionisothermalprocessofanidealgasW,=P,V,ln(V2/V)AE.(KJ)E-EouEnergyBalancesyatenNet enengy tnansferChange in intemal,kioctic.foranysystemandanyprocessbyhealwortandmasspoteatial,tc,enengis1stlawforclosedsystem=WWWWQ=Qnetin=0-0aet.ououtEnergyBalanceforclosedsystemO-W=AEThe energyrequired to raise T of 1kg ofa substanceby 1K,kJ/(kg.k)ahSpecific heatCv atconstant1Cp atconstantPCp22aTIdealgases:Cp=Cv+R;k=Cp/CvForsolidsand liquids,Cp=Cv=cU,h fromtable.Ah=h-hc,(T)dTepavg(T-T)Changes ofu, h for ideal gasesByusingCvorCpUsingaveragespecificheats.Cv,avg=Cv(T2/2+T1/2)Cp,avg=Cp(T2/2+T1/2)Forimcompressiblec(T)dT=Cav(T2-T)Ah=Au+VAPChanges of u,h for solid/fluidsubstances
Chap4 Summary 2 The work associated with expansion and compression 1st law for closed system General: δWb=Pdv, P-V diagram U,h from table. Specific heat Changes of u, h for ideal gases Changes of u, h for solid/fluid Boundary work Energy Balance for any system and any process Isobaric process, PVn=const Polytropic process isothermal process of an ideal gas Wb=P1V1ln(V2/V1) The energy required to raise T of 1kg of a substance by 1K, kJ/(kg.k) By using Cv or Cp Using average specific heats. Cv,avg=Cv(T2/2+T1/2) Cp,avg=Cp(T2/2+T1/2) Energy Balance for closed system Cv at constant V Cp at constant P Ideal gases: Cp=Cv+R; k=Cp/Cv For solids and liquids, Cp=Cv=C For imcompressible substances
Chapter 4 Energy analysis of closed systemsmoving boundary work or P dVwork general energy balance applied to closed systemsCp,Cy -specific heat at constant pressure/volumeincompressible substances , the changes in their internalenergy and enthalpy Solve energy balance problems for closed (fixed mass)systems that involve heat and work interactions forgeneral pure substances, ideal gases, andincompressiblesubstances
Chapter 4 Energy analysis of closed systems • moving boundary work or P dV work • general energy balance applied to closed systems. • Cp ,Cv -specific heat at constant pressure/volume • incompressible substances , the changes in their internal energy and enthalpy. • Solve energy balance problems for closed (fixed mass) systems that involve heat and work interactions for general pure substances, ideal gases, and incompressible substances. 3
4-1 Moving Boundary WorkMovingboundarywork:oneformofmechanicalworkassociatedwiththeexpansionorcompressionofagasinadevicelikecarengines. PdVExpansionworkCompressionworkThemost common formofmechanical workFor real engines (compressors),to analyze the moving boundarywork.Piston moves at very higherspeed.StatesarehardtodefineProcessesPathWork-pathfunctionGAS
4-1 Moving Boundary Work • Moving boundary work: one form of mechanical work associated with the expansion or compression of a gas in a device like car engines. PdV – Expansion work – Compression work – The most common form of mechanical work • For real engines (compressors), to analyze the moving boundary work. – Piston moves at very higher speed. – States are hard to define – Processes – Path – Work- path function 4
4-1 Moving Boundary Work:Aquasi-equilibriumprocess:thesystemremainsnearlyinequilibriumat all times of a process.ApproximationMaximum work output(engines)minimumworkinput (compressors)ReversibleprocessSW.=Fds=PAds=PdVP-absolutepressure, positivedVpositivefor expansionprocess,negativeforcompressionprocessGASThis explains why the moving boundary work is called PdV work
4-1 Moving Boundary Work • A quasi-equilibrium process: the system remains nearly in equilibrium at all times of a process. – Approximation – Maximum work output (engines) – minimum work input (compressors) • Reversible process • This explains why the moving boundary work is called PdV work 5 P-absolute pressure, positive dV—positive for expansion process, negative for compression process