Chap6 Summary-1Whyweneed2ndLaw?Allprocessessatisfy1stLawSatisfying1stdoesnotensuretheprocesscanactuallyoccurIntroductionto2ndLawAprocesshasdirectionEnergyhasqualityandquantityHeat SinkHeat SourceHeatengineThermalenergyReservoirWact.ouOReceiveheatQfromahightemperature sourceHMthQHWConvert part Qtowork Wnet.outnetoutOHeatEnginesQTihRejectwaste heatQtoalowtemperature sink92ndlawKelvin-PlanckStatement:Itisimpossibleforanydevicethatoperatesonacycletoreceiveheatfromasinglereservoirandproduceanetamountofwork.Noheatenginecanhaven=100%Refrigerators/heatpump:ThedevicesdriveheatQtransferfromT,toTHW.RefrigeratorThework inputtotherefrigerator/heatpumpnet,inwants QLQHeatQabsorbedfromrefrigeratedspaceTHeatpumpQHHeatQrejectedtohightemperature THwants QHRefrigerator,HeatPumpDesiredoulputuDesired outputQ,AirCOPCOPHCOPW.WreLinRequired inputRequired inputConditionerDCEI2nd law,Clausius Statement:Heatdoesnot,of its ownvolition,transferfromacoldmediumtoawarmerone.（热不能自发地、不付代价地从低温物体传到高温物体）
Chap6 Summary-1 1 Why we need 2nd Law? All processes satisfy 1st Law; Satisfying 1st does not ensure the process can actually occur Heat Engines Refrigerator, Heat Pump Introduction to 2nd Law Refrigerators/heat pump: The devices drive heat Q transfer from TL to TH, Thermal energy Reservoir Receive heat QH from a high temperature source The work input to the refrigerator/heat pump Heat QL absorbed from refrigerated space TL A process has direction Energy has quality and quantity Heat Source Heat Sink Convert part QH to work Wnet,out Reject waste heat QL to a low temperature sink Heat engine 2nd law, Kelvin-Planck Statement: It is impossible for any device that operates on a cycle to receive heat from a single reservoir and produce a net amount of work. No heat engine can have η=100% Heat QH rejected to high temperature TH Refrigerator wants QL Heat pump wants QH COP 2nd law, Clausius Statement: Heat does not, of its own volition, transfer from a cold medium to a warmer one. (热不能自发地、不付代价地从低温物体传到高温 物体) Air Conditioner
Chap6 Summary-2SystemAprocesscanbereversedwithouleavinganytraceonthesurroundingsSurroundingsReversible ProcessesInternal RevExternal RevWhy need RevIrreversible:heattransferThe bestknown reversible cycle; four reversible processesIsothermal expansionAdiabatic expansionIsothermalCompressionAdiabaticcompressionCarnotCycleCarnotheatengineReversed CarnotCycleCarnotrefrigerator/heat pumpCarnot Principle 1:Given T,andTh,Nth.irrev<.Nth,revCarnot Principle 2:GivenT,andTh,Nth.all rev=Nth,revThe heat engine operates on the reversible Carnot Cycleirreversibleheat engineMhrevCarnot HeatEngineTLQLreversible heat engineTth,revThTih.revTHOn二impossibleheatengineTih,reyThe refrigerator / heat pump operates on a reversible Carnot CycleCarnotRefrigeratorCOPR.ECOPRIEVirreversiblerefrigeratoTH/T,-1Carnot Heat PumpCOPCOPRrevreversiblerefrigeratorCOPHPeCOPR.revimpossiblerefrigeratorI-TL/TH2
Chap6 Summary-2 2 A process can be reversed without leaving any trace on the surroundings. Carnot Cycle Carnot Refrigerator Carnot Heat Pump Reversible Processes The heat engine operates on the reversible Carnot Cycle The best known reversible cycle; four reversible processes Carnot heat engine Carnot Principle 1: Given TL and TH, ηth,irrev < ηth,rev System Surroundings Internal Rev External Rev Why need Rev Irreversible: heat transfer Isothermal expansion Isothermal Compression Adiabatic compression Reversed Carnot Cycle Carnot refrigerator /heat pump Carnot Principle 2: Given TL and TH, ηth,all rev = ηth,rev Carnot Heat Engine The refrigerator / heat pump operates on a reversible Carnot Cycle Adiabatic expansion
Chap7 SummaryClausiusinequality:thecyclicintegral ofisalways≤zeroEntropy（熵）60QAS= S, - SiASEntropyIsoTTotintrevEntropychangeofaclosedsystemASm=S,-S,ReversibleprocessIrreversibleprocess2ASm-S1-S1-JSm= S, - S,>IncreaseofEntropySgen≥0Principle(增原理Increaseofentropyprinciple（孤立系统炳增原理，简称摘增原理）：theentropyofanisolatedsystemduringaprocessalwaysincreaseor,inthelimitingcaseofareversibleprocessremainsconstant.（孤立系统的焰可以增大，或保持不变，但不可能减少）AS=mAS=m(S.EntropychangeofpuresubstancesS0,0,ASsys=S.S2,IsentropicprocessadibaticReversibleas=03,T-S,h-sdiagramsdsAeSomeremarks4,The3rd lawof thermodaynamics:The entropy ofapurecrystallinesubstance atabsolutezerotemperatureiszerodhvdpPdvdudsas5,Tds relationsTTTT6,reversibleworkoutputAkeADC
Chap7 Summary 3 Clausius inequality: the cyclic integral of is always ≦ zero Increase of Entropy Principle(熵增原理) Entropy (熵) 1, Entropy change of pure substances: Entropy change of a closed system: Increase of entropy principle (孤立系统熵增原理，简称熵增原理)：the entropy of an isolated system during a process always increase or , in the limiting case of a reversible process remains constant. (孤立系统的熵可以增大，或保持不变，但不可能减少) Entropy Some remarks Iso T Reversible process Irreversible process ≥ 0 sf at 0.01℃=0 kJ/kg.k 2, Isentropic process 0, adibatic 0, Reversible 3, T-S, h-s diagrams = 4, The 3rd law of thermodaynamics: The entropy of a pure crystalline substance at absolute zero temperature is zero 5, T ds relations: 6, reversible work output >
Chapter 7 Entropy
Chapter 7 Entropy 4
7-1 EntropyThe 2nd law of thermodynamics leads toexpressions that involve inequalitiesHeat engine:Nth,irrev< Nth,rev- Heat pump: COPHP,irev< COPHP,rev COPR,irev < COPR,rev :Clausius inequality:Thecyclicintegralofisalwayslessthanorequal tozero.Stated byR.J.E.Clausius.Valid for all cycles, reversible or irreversibleThecyclicintegral ofcanbeviewed asthe sumof all thesedifferential amounts of heat transfer divided by the temperature of theboundary
7-1 Entropy • The 2nd law of thermodynamics leads to expressions that involve inequalities. – Heat engine:ηth,irrev< ηth,rev – Heat pump: COPHP,irrev < COPHP,rev COPR,irrev < COPR,rev ; • Clausius inequality: – The cyclic integral of is always less than or equal to zero. – Stated by R.J.E. Clausius. – Valid for all cycles, reversible or irreversible – The cyclic integral of can be viewed as the sum of all these differential amounts of heat transfer divided by the temperature of the boundary. 5