Chap6 Summary-1Whyweneed2ndLaw?Allprocessessatisfy1stLaw,Satisfying1stdoesnotensuretheprocesscanactuallyoccurIntroductionto2ndLawAprocesshasdirectionEnergyhasqualityandquantityHeat SinkHeat SourceHeatengineThermalenergyReservoirWact.ouOReceiveheatQfromahightemperature sourceHMthQHWConvert part Q to work Wnet.outnetoutOHeatEnginesQTihRejectwaste heatQtoalowtemperature sink92ndlawKelvin-PlanckStatement:Itisimpossibleforanydevicethatoperatesonacycletoreceiveheatfromasinglereservoirandproduceanetamountofwork.No heat engine can haven=100%Refrigerators/heatpump:ThedevicesdriveheatQtransferfromT,toTHW.RefrigeratorTheworkinputtotherefrigerator/heatpumpnet,inwants QLQHeatQabsorbedfromrefrigeratedspaceTHeatpumpQHHeat Qrejected tohightemperature 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）6
Chap6 Summary-1 6 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/TH
Chap6 Summary-2 7 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