192ndLawofThermodynamics熱力學(xué)第二定律課件

19.2ndLawofThermodynamics熱力學(xué)第二定律Reversibility&Irreversibility 1.可逆性和不可逆性The2ndLawofThermodynamics 2.熱力學(xué)第二定律Applicationsofthe2ndLaw 3.第二定律的應(yīng)用Entropy&EnergyQuality 4.熵和能量品質(zhì)19.2ndLawofThermodynamicsMostenergyextractedfromthefuelinpowerplantsisdumpedtotheenvironmentaswasteheat,hereusingalargecoolingtower.發(fā)電廠內(nèi)從燃料抽取的能量，大部份都被當(dāng)成廢熱而丟到環(huán)境裏；圖中用的是一個(gè)大型冷卻塔。Whyissomuchenergywasted?為甚麼浪費(fèi)這麼多能量？2ndlaw:noQWwith100%efficiency第二定律：沒有QW可以達(dá)到100%効率。MostenergyextractedfromtheEfficiencies 効率Engine引擎Efficiency効率Gasoline汽油18~20%Diesel柴油upto可達(dá)40%Steam蒸氣~8%GasTurbine氣渦輪upto可達(dá)40%PowerPlant發(fā)電廠Efficiency効率Coal燃煤36%Nuclear核子30%Efficiencies 効率Engine引擎Effic19.1.Reversibility&Irreversibility可逆性和不可逆性Blocksloweddown 質(zhì)塊因摩擦力byfriction: 而慢下來:Irreversible 不可逆Bouncingball: 彈跳的球:

reversible 可逆Examplesofirreversibleprocesses:不可逆程序範(fàn)例:Beatinganegg,blendingyolk&white打一個(gè)蛋，蛋黃蛋白混成一團(tuán)Cupsofcold&hotwaterincontact幾杯冷和熱水貼在一起Spontaneousprocess: 自發(fā)性程序:orderdisorder 有序無(wú)序(statisticallymoreprobable) (統(tǒng)計(jì)上較有可能)時(shí)間19.1.Reversibility&IrreversGOTIT?19.1.Whichoftheseprocessesareirreversible: 以下那些程序是不可逆的：stirringsugarintocoffee, (a)把糖攪進(jìn)咖啡中，buildingahouse, (b)建一幢房子，demolishingahousewithawreckingball, (c)用鐵球撞毀一幢房子，demolishingahousebytakingitapartpiecebypiece, (d)把房子逐塊拆下，harnessingtheenergyoffallingwatertodrivemachinery,(e)利用水下墮的能量驅(qū)動(dòng)機(jī)器，harnessingtheenergyoffallingwatertoheatahouse? (f)利用水下墮的能量加熱房子？GOTIT?19.1.Whichofthesep19.2.The2ndLawofThermodynamics熱力學(xué)第二定律Heatengineextractsworkfromheatreservoirs.熱引擎從熱庫(kù)取熱。gasoline&dieselengines 汽油和柴油引擎fossil-fueled&nuclearpowerplants 化石燃料和核子發(fā)電廠jetengines 噴射引擎2ndlawofthermodynamics(Kelvin-Planckversion):Thereisnoperfectheatengine.熱力學(xué)第二定律

(凱爾文-普朗克版)：沒有完美熱引擎。Perfectheatengine:covertsheattoworkdirectly.

完美熱引擎:把熱直接變成功。熱庫(kù)Heatdumped倒掉的廢熱Noprocessispossibleinwhichthesoleresultistheabsorptionofheatfromareservoiranditscompleteconversionintowork.沒有任何程序的淨(jìng)効果可以是從單一個(gè)熱庫(kù)吸收熱量，然後把它全部變成功。19.2.The2ndLawofThermodynsimpleheatengine簡(jiǎn)單熱引擎

cylindercompressedadiabatically氣缸絕熱地壓縮(TrisestoThadiabaticallyT絕熱地升至Th

)gasincontactwithTh,expandsisothermallytodowork;heatQh=Whabsorbed氣缸與Th接觸，氣體等溫膨脹作工；吸進(jìn)Qh=Wh的熱

cylinderexpandsadiabatically氣缸絕熱地膨脹(TdropstoTcadiabaticallyT絕熱地降至Tc

)cylinderincontactwithTc,gascompressedisothermallyheat

Qc=Wcdumped氣缸與Tc接觸，氣體等溫壓縮；倒出Qc=Wc的熱Efficiency効率(anyengine)任何引擎(Simpleengine)簡(jiǎn)單引擎(anycycle)任何循環(huán)simpleheatenginecylinderCarnotEngine(Cycle) 卡諾引擎(循環(huán))Isothermalexpansion等溫膨脹: T=Th,W1=Qh>0Adiabaticexpansion絕熱膨脹: Th

Tc,W2>0Isothermalcompression等溫壓縮: T=Tc,W3=Qc<04.Adiabaticcompression絕熱壓縮: Tc

Th,W4=W2<0Idealgas理想氣體：Adiabaticprocesses絕熱程序：AB:Heatabs.吸收了熱CD:Heatrej.排出熱BC:Workd.做了功DA:Workd.被做了功CarnotEngine(Cycle) 卡諾引擎(循環(huán)Example19.1.CarnotEngine卡諾引擎ACarnotengineextracts240JfromitshighTreservoirduringeachcycle,&rejects100Jtotheenvironmentat15C.一部卡諾引擎每週期從它的高T熱庫(kù)提取240J，再於15C向外丟出100J。Howmuchworkdoestheenginedoineachcycle?引擎每週期作功多少？What’sitsefficiency? 它的功率為何？What’stheTofthehotreservoir? 高溫?zé)釒?kù)的T為何？workdone所作功Efficiency功率Example19.1.CarnotEngineEngines,Refrigerators,&the2ndLaw

引擎，冷凍機(jī)，和第二定律Carnot’stheorem卡諾定理:AllCarnotenginesoperatingbetweentemperaturesTh&Tchavethesameefficiency.所有在溫度Th&Tc

之間運(yùn)作的卡諾引擎都有同樣的効率。NootherengineoperatingbetweenTh&Tccanhaveagreaterefficiency.沒有其他在溫度Th&Tc

之間運(yùn)作的引擎可以有更大的効率。Refrigerator:extractsheatfromcoolreservoirintoahotone.冷凍機(jī):從冷庫(kù)抽送熱量到一個(gè)熱庫(kù)。workrequired所需功Engines,Refrigerators,&th2ndlawofthermodynamics(Clausiusversion):Thereisnoperfectrefrigerator.熱力學(xué)第二定律

(克勞修斯版)：沒有完美冷凍機(jī)。perfectrefrigerator:movesheatfromcooltohotreservoirwithoutworkbeingdoneonit.完美冷凍機(jī)：不用對(duì)它作功就可以把熱量從低移到高溫?zé)釒?kù)。Noprocessispossiblewhosesoleresultisthetransferofheatfromabodyoflowertemperaturetoabodyofhighertemperature.沒有任何程序的淨(jìng)効果可以是把熱從一個(gè)較低溫的物體送到一個(gè)較高溫的物體。2ndlawofthermodynamics(ClPerfectrefrigerator

Perfectheatengine完美冷凍機(jī)

完美熱引擎 ClausiusKelvin-Planck

克勞修斯

凱爾文-普朗克完美冷凍機(jī)完美熱引擎實(shí)在的熱引擎PerfectrefrigeratorPerf

Carnotengineismostefficient

卡諾引擎效率最高eCarnot=thermodynamicefficiency

熱力效率eCarnot

erev>eirrevCarnotrefrigerator卡諾冷凍機(jī),e=60%Hypotheticalengine

假想引擎,e=70%完美熱引擎Carnotengineismostef19.3.Applicationsofthe2ndLaw第二定律的應(yīng)用Powerplant發(fā)電廠fossil-fuel化石燃料:Th=650K

Nuclear核能:Th=570K

Tc=310KActualvalues實(shí)在數(shù)值:efossil~40% enuclear

~34% ecar~20%Prob54&55Heatsource熱源Boiler鍋爐Turbine渦輪機(jī)Generator發(fā)電機(jī)Electricity電Condenser冷凝器Wastewater廢水Coolingwater冷卻用水溫度溫度溫度水蒸氣水入出19.3.Applicationsofthe2ndApplication:Combined-CyclePowerPlant

應(yīng)用:聯(lián)合-循環(huán)發(fā)電廠Turbineengines:highTh(1000K2000K)&Tc(800K)…notefficient.渦輪機(jī):高Th(1000K2000K)&Tc(800K)…無(wú)効率。Steamengines:Tc~ambient300K.蒸氣機(jī):Tc~周圍的300K.Combined-cycle聯(lián)合-循環(huán):Th(1000K2000K)&Tc(300K)…e~60%Application:Combined-CyclePExample19.2.Combined-CyclePowerPlant

聯(lián)合-循環(huán)發(fā)電廠Thegasturbineinacombined-cyclepowerplantoperatesat1450C.一個(gè)聯(lián)合-循環(huán)發(fā)電廠內(nèi)的氣渦輪機(jī)在1450C下運(yùn)作。Itswasteheatat500Cistheinputforaconventionalsteamcycle,withitscondenserat8C.它的500C廢熱輸入另一個(gè)冷凝器在8C的傳統(tǒng)蒸氣循環(huán)。Findeofthecombined-cycle,&compareitwiththoseoftheindividualcomponents.求此聯(lián)合-循環(huán)的e，並與其個(gè)別組件的值比較。氣渦輪機(jī)燃燒溫度氣渦輪機(jī)蒸氣循環(huán)中介溫度冷卻水溫度Example19.2.Combined-CycleRefrigerators冷凍機(jī)Coefficientofperformance(COP)forrefrigerators:冷凍機(jī)的績(jī)效系數(shù)COPishighifTh

Tc.Th

Tc時(shí)COP高M(jìn)ax.theoreticalvalue(Carnotcycle)理論最大值(卡諾循環(huán))1stlawW=0(COP=)formovingQwhenTh

=Tc.若Th

=Tc

，移動(dòng)Q時(shí)W=0(COP=)。Refrigerators冷凍機(jī)CoefficientoExample19.3.HomeFreezer家用冰箱AtypicalhomefreezeroperatesbetweenTc=18CtoTh=30C.家用冰箱通常都在Tc=18C到Th=30C之間運(yùn)作。What’sitsmaximumpossibleCOP? 它可能的最大COP值為何？WiththisCOP,howmuchelectricalenergywouldittaketofreeze500gofwaterinitiallyat0C?在這COP值之下，需要多少電能才可以把500g在0C的水凝固？Table17.12ndlaw:onlyafractionofQcanbecomeWinheatengines.第二定律：熱引擎中祇有一部份Q能變成W。 alittleWcanmovealotofQinrefrigerators.

冷凍機(jī)內(nèi)一點(diǎn)W可以產(chǎn)生很多Q。Example19.3.HomeFreezerHeatPumps熱泵HeatpumpasAC:以熱泵作冷氣機(jī)Heatpumpasheater:以熱泵作暖爐Groundtemp~10Cyearround土地溫度整年都~10CHeatpump:movesheatfromTctoTh.HeatPumps熱泵HeatpumpasAGOTIT?19.2.AcleverengineerdecidestoincreasetheefficiencyofaCarnotenginebycoolingthelow-TreservoirusingarefrigeratorwiththemaximumpossibleCOP.一個(gè)聰明的工程師決定要提高卡諾引擎的効率，方法是用一部具有最大COP可能值的冷凍機(jī)來冷卻低溫?zé)釒?kù)。Willtheoverallefficiencyofthissystem這系統(tǒng)的整體效率會(huì)exceed 超過，belessthan 低於，equalthatof 等於theoriginalenginealone 原來引擎本身的值？seeProb32forproof證明可參考Prob32GOTIT?19.2.Acleverenginee19.4.Entropy&EnergyQuality 熵和能量品質(zhì)EnergyqualityQmeasurestheversatilityofdifferentenergyforms.能量品質(zhì)

Q衡量各種能量的可用性。2ndlaw:Energyofhigherqualitycanbeconvertedcompletelyintolowerqualityform.第二定律：高質(zhì)能量可以完全變成較低質(zhì)能量Butnotviceversa.反之卻不成。最高質(zhì)最低質(zhì)機(jī)械，電能高溫低溫19.4.Entropy&EnergyQualityConceptualExample19.1.EnergyQuality,EndUse,&Cogeneration

能量品質(zhì)，終端使用，和共發(fā)電Youneedanewwaterheater,&you’retryingtodecidebetweengas&electric.你需要一個(gè)新的熱水器；現(xiàn)正在瓦斯和電熱兩者之間作一選擇。Thegasheateris85%efficient,meaning85%ofthefuelenergygoesintoheatingwater.瓦斯熱水器的効率是85%，亦即85%的燃料能可以用來熱水。Theelectricheaterisessentially100%efficient. 電熱水器的効率可說是100%。Thermodynamically,whichheatermakesthemostsense? 從熱力學(xué)來看，那一個(gè)熱水器比較值得用?Cogeneration共發(fā)電:WasteheatfromelectricitygenerationusedforlowQneeds.發(fā)電時(shí)產(chǎn)生的廢熱用在低Q的需求上。Ans. 答Only1/3offuelenergyisconvertedtoelectricityatapowerplant.發(fā)電廠祗把燃料能的1/3轉(zhuǎn)成電能。Withthisinmind,thegasheaterisabetterchoice.在這考量下，瓦斯熱水器是較佳選擇。ConceptualExample19.1.EnerMakingtheConnection 連起來Iftheelectricitycomesfromamoreefficientgas-firedpowerplantwithe=48%,假設(shè)電力來自効率較佳，e=48%，的天然氣發(fā)電廠，comparethegasconsumptionofyourtwoheaterchoices.比較上述兩種熱水器的瓦斯消耗。Gasheater: 1unitoffuelenergybecomes0.85unitofheat.瓦斯熱水器: 1單位的燃料能可變成0.85單位的熱。Electricheater: 1unitoffuelenergybecomes0.48unitofelectricenergy,電熱水器: 1單位的燃料能可變成0.48單位的電能， thenbecomes0.48unitofheat.

再變成0.48單位的熱。Electricheaterconsumes0.85/0.48=1.8timesthefuelconsumedbygasheater.電熱水器消耗0.85/0.48=1.8倍瓦斯熱水器所需的燃料。MakingtheConnection 連起來IfthEntropy 熵lukewarm:can’tdoW,Q

微溫：不能作功，Q

Carnotcycle(reversibleprocesses):卡諾循環(huán)(可逆程序)Qh=heatabsorbed所吸熱Qc=heatrejected所排熱Qh,Qc=heatabsorbed 所吸熱C=anyclosedpath任何閉口路徑S=entropy

熵[S]=J/KIrreversibleprocessescan’tberepresentedbyapath.不可逆程序不能以路徑表達(dá)。等溫線體積壓力絕熱線C=Carnotcycle卡諾循環(huán)Contour=sumofCarnotcycles.路徑=所有卡諾循環(huán)之和Entropy 熵lukewarm:can’tdoW,Entropy 熵lukewarm:can’tdoW,Q

微溫：不能作功，Q

Carnotcycle(reversibleprocesses):卡諾循環(huán)(可逆程序)Qh=heatabsorbed所吸熱Qc=heatrejected所排熱Qh,Qc=heatabsorbed 所吸熱C=anyclosedpath任何閉口路徑S=entropy

熵[S]=J/KIrreversibleprocessescan’tberepresentedbyapath.不可逆程序不能以路徑表達(dá)。等溫線體積壓力絕熱線C=Carnotcycle卡諾循環(huán)Entropy 熵lukewarm:can’tdoW,Entropychangeispath-independent.熵變量與路徑無(wú)關(guān)。(Sisathermodynamicvariable)(S是一個(gè)熱力變數(shù))S=0overanyclosedpath任何閉口路徑上，S=0

S21

+

S12=0

S21

=

S21

Entropychangeispath-indepenEntropyinCarnotCycle 卡諾循環(huán)的熵Idealgas理想氣體：Adiabaticprocesses絕熱程序：Heatabsorbed:吸收的熱Heatrejected:排出的熱EntropyinCarnotCycle 卡諾循環(huán)的熵IrreversibleHeatTransfer 不可逆熱傳遞Cold&hotwatercanbemixedreversiblyusingextraheatbaths.冷和熱水可以用額外的熱庫(kù)來達(dá)成可逆性混合。Actualmixing,irreversibleprocesses原來的混合，不可逆程序reversibleprocesses可逆程序T1=somemediumT.某個(gè)中介T。T2=somemediumT.某個(gè)中介T。IrreversibleHeatTransfer 不可逆AdiabaticFreeExpansion 絕熱性自由膨脹Adiabatic 絕熱Qad.exp.=0Scanbecalculatedbyanyreversibleprocessbetweenthesamestates.p=const. p=定值Can’tdowork 不能作功Qdegraded. Q被貶。

S可從兩態(tài)之間任何可逆程序計(jì)算真空提取功拿走隔板氣隔板isothermal等溫

AdiabaticFreeExpansion 絕熱性自由Entropy&AvailabilityofWork熵與可用的功Beforeadiabaticexpansion,gascandoworkisothermally絕熱膨脹之前，氣體可以在等溫下作功Afteradiabaticexpansion,gascannotdowork,whileitsentropyincreasesby絕熱膨脹之後，氣體不能作功，它的熵則增加了Inageneralirreversibleprocess在一個(gè)廣泛的不可逆程序中CoolestTinsystemEntropy&AvailabilityofWorkExample19.4.

LossofQ Q的損耗A2.0Lcylindercontains5.0molofcompressedgasat300K.一個(gè)2.0L氣筒灌了5.0mol在300K的壓縮氣體。Ifthecylinderisdischargedintoa150Lvacuumchamber&itstemperatureremainsat300K,如果氣筒往一個(gè)150L真空倉(cāng)放氣，而且它的溫度保持在300K，howmuchenergybecomesunavailabletodowork?有多少能量變成不能作功？閥打開之前氣閥關(guān)上真空之後Example19.4.LossofQ Q的損耗AStatisticalInterpretationofEntropy 熵的統(tǒng)計(jì)詮釋Gasof2distinguishablemoleculesoccupying2sidesofabox由可存在盒子兩邊的兩個(gè)可分辨分子所組成的氣體Microstates微觀態(tài)Macrostates巨觀態(tài)probabilityofmacrostate巨觀態(tài)的或然率

1/42?=?1/4AStatisticalInterpretationoGasof4distinguishablemoleculesoccupying2sidesofabox由可存在盒子兩邊的4個(gè)可分辨分子所組成的氣體Microstates微觀態(tài)Macrostates巨觀態(tài)probabilityofmacrostate巨觀態(tài)的或然率

1/16=0.0641/16=?=0.2541/16=?=0.251/16=0.0661/16=3/8=0.38Gasof4distinguishablemolecGasof100molecules100個(gè)分子的氣體Gasof1023molecules1023個(gè)分子的氣體Equaldistributionofmolecules分子平均分佈或然率Statisticaldefinitionofentropy:熵的統(tǒng)計(jì)定義：#ofmicrostates=微觀態(tài)數(shù)目Gasof100moleculesGasof102Entropy&the2ndLawofThermodynamics

熵與熱力學(xué)第二定律2ndLawofThermodynamics:熱力學(xué)第二定律inanyclosedsystem任何密閉系統(tǒng)中Scandecreaseinanopensystembyoutsideworkonit.S可以在一個(gè)開放系統(tǒng)中因外界對(duì)它作功而減少。However,S0forcombinedsystem.不過，如果把”外界”也算進(jìn)來，整個(gè)系統(tǒng)還是S0。 S0intheuniverse 整個(gè)宇宙S0 Universetendstodisorder 宇宙趨向混亂Life生命?Entropy&the2ndLawofThermGOTIT?19.3.Ineachofthefollowingprocesses,doestheentropyofthenamedsystem increase,decrease,orstaythesame?在下列每個(gè)程序中，熵在提到的系統(tǒng)裏是增加，減少，或是不變？aballooninflates 氣球充氣cellsdifferentiateinagrowingembryo,formingdifferentorgans細(xì)胞在成長(zhǎng)中的胚胎裏分化，形成各種器官ananimaldies,itsremainsgraduallydecays 一個(gè)動(dòng)物死了，它的遺體慢慢腐爛anearthquakedemolishesabuilding 一場(chǎng)地震把一幢建築物毀了aplantutilizesunlight,CO2,&watertomanufacturesugar一棵植物用陽(yáng)光，CO2

，和水來制做糖apowerplantburnscoal&produceselectricalenergy 一所發(fā)電廠燒煤來產(chǎn)生電能acar’sfrictionbasedbrakesstopthecar. 以摩擦力為主的剎車把車子停下來。GOTIT?19.3.Ineachofthef19.2ndLawofThermodynamics熱力學(xué)第二定律Reversibility&Irreversibility 1.可逆性和不可逆性The2ndLawofThermodynamics 2.熱力學(xué)第二定律Applicationsofthe2ndLaw 3.第二定律的應(yīng)用Entropy&EnergyQuality 4.熵和能量品質(zhì)19.2ndLawofThermodynamicsMostenergyextractedfromthefuelinpowerplantsisdumpedtotheenvironmentaswasteheat,hereusingalargecoolingtower.發(fā)電廠內(nèi)從燃料抽取的能量，大部份都被當(dāng)成廢熱而丟到環(huán)境裏；圖中用的是一個(gè)大型冷卻塔。Whyissomuchenergywasted?為甚麼浪費(fèi)這麼多能量？2ndlaw:noQWwith100%efficiency第二定律：沒有QW可以達(dá)到100%効率。MostenergyextractedfromtheEfficiencies 効率Engine引擎Efficiency効率Gasoline汽油18~20%Diesel柴油upto可達(dá)40%Steam蒸氣~8%GasTurbine氣渦輪upto可達(dá)40%PowerPlant發(fā)電廠Efficiency効率Coal燃煤36%Nuclear核子30%Efficiencies 効率Engine引擎Effic19.1.Reversibility&Irreversibility可逆性和不可逆性Blocksloweddown 質(zhì)塊因摩擦力byfriction: 而慢下來:Irreversible 不可逆Bouncingball: 彈跳的球:

reversible 可逆Examplesofirreversibleprocesses:不可逆程序範(fàn)例:Beatinganegg,blendingyolk&white打一個(gè)蛋，蛋黃蛋白混成一團(tuán)Cupsofcold&hotwaterincontact幾杯冷和熱水貼在一起Spontaneousprocess: 自發(fā)性程序:orderdisorder 有序無(wú)序(statisticallymoreprobable) (統(tǒng)計(jì)上較有可能)時(shí)間19.1.Reversibility&IrreversGOTIT?19.1.Whichoftheseprocessesareirreversible: 以下那些程序是不可逆的：stirringsugarintocoffee, (a)把糖攪進(jìn)咖啡中，buildingahouse, (b)建一幢房子，demolishingahousewithawreckingball, (c)用鐵球撞毀一幢房子，demolishingahousebytakingitapartpiecebypiece, (d)把房子逐塊拆下，harnessingtheenergyoffallingwatertodrivemachinery,(e)利用水下墮的能量驅(qū)動(dòng)機(jī)器，harnessingtheenergyoffallingwatertoheatahouse? (f)利用水下墮的能量加熱房子？GOTIT?19.1.Whichofthesep19.2.The2ndLawofThermodynamics熱力學(xué)第二定律Heatengineextractsworkfromheatreservoirs.熱引擎從熱庫(kù)取熱。gasoline&dieselengines 汽油和柴油引擎fossil-fueled&nuclearpowerplants 化石燃料和核子發(fā)電廠jetengines 噴射引擎2ndlawofthermodynamics(Kelvin-Planckversion):Thereisnoperfectheatengine.熱力學(xué)第二定律

(凱爾文-普朗克版)：沒有完美熱引擎。Perfectheatengine:covertsheattoworkdirectly.

完美熱引擎:把熱直接變成功。熱庫(kù)Heatdumped倒掉的廢熱Noprocessispossibleinwhichthesoleresultistheabsorptionofheatfromareservoiranditscompleteconversionintowork.沒有任何程序的淨(jìng)効果可以是從單一個(gè)熱庫(kù)吸收熱量，然後把它全部變成功。19.2.The2ndLawofThermodynsimpleheatengine簡(jiǎn)單熱引擎

cylindercompressedadiabatically氣缸絕熱地壓縮(TrisestoThadiabaticallyT絕熱地升至Th

)gasincontactwithTh,expandsisothermallytodowork;heatQh=Whabsorbed氣缸與Th接觸，氣體等溫膨脹作工；吸進(jìn)Qh=Wh的熱

cylinderexpandsadiabatically氣缸絕熱地膨脹(TdropstoTcadiabaticallyT絕熱地降至Tc

)cylinderincontactwithTc,gascompressedisothermallyheat

Qc=Wcdumped氣缸與Tc接觸，氣體等溫壓縮；倒出Qc=Wc的熱Efficiency効率(anyengine)任何引擎(Simpleengine)簡(jiǎn)單引擎(anycycle)任何循環(huán)simpleheatenginecylinderCarnotEngine(Cycle) 卡諾引擎(循環(huán))Isothermalexpansion等溫膨脹: T=Th,W1=Qh>0Adiabaticexpansion絕熱膨脹: Th

Tc,W2>0Isothermalcompression等溫壓縮: T=Tc,W3=Qc<04.Adiabaticcompression絕熱壓縮: Tc

Th,W4=W2<0Idealgas理想氣體：Adiabaticprocesses絕熱程序：AB:Heatabs.吸收了熱CD:Heatrej.排出熱BC:Workd.做了功DA:Workd.被做了功CarnotEngine(Cycle) 卡諾引擎(循環(huán)Example19.1.CarnotEngine卡諾引擎ACarnotengineextracts240JfromitshighTreservoirduringeachcycle,&rejects100Jtotheenvironmentat15C.一部卡諾引擎每週期從它的高T熱庫(kù)提取240J，再於15C向外丟出100J。Howmuchworkdoestheenginedoineachcycle?引擎每週期作功多少？What’sitsefficiency? 它的功率為何？What’stheTofthehotreservoir? 高溫?zé)釒?kù)的T為何？workdone所作功Efficiency功率Example19.1.CarnotEngineEngines,Refrigerators,&the2ndLaw

引擎，冷凍機(jī)，和第二定律Carnot’stheorem卡諾定理:AllCarnotenginesoperatingbetweentemperaturesTh&Tchavethesameefficiency.所有在溫度Th&Tc

之間運(yùn)作的卡諾引擎都有同樣的効率。NootherengineoperatingbetweenTh&Tccanhaveagreaterefficiency.沒有其他在溫度Th&Tc

之間運(yùn)作的引擎可以有更大的効率。Refrigerator:extractsheatfromcoolreservoirintoahotone.冷凍機(jī):從冷庫(kù)抽送熱量到一個(gè)熱庫(kù)。workrequired所需功Engines,Refrigerators,&th2ndlawofthermodynamics(Clausiusversion):Thereisnoperfectrefrigerator.熱力學(xué)第二定律

(克勞修斯版)：沒有完美冷凍機(jī)。perfectrefrigerator:movesheatfromcooltohotreservoirwithoutworkbeingdoneonit.完美冷凍機(jī)：不用對(duì)它作功就可以把熱量從低移到高溫?zé)釒?kù)。Noprocessispossiblewhosesoleresultisthetransferofheatfromabodyoflowertemperaturetoabodyofhighertemperature.沒有任何程序的淨(jìng)効果可以是把熱從一個(gè)較低溫的物體送到一個(gè)較高溫的物體。2ndlawofthermodynamics(ClPerfectrefrigerator

Perfectheatengine完美冷凍機(jī)

完美熱引擎 ClausiusKelvin-Planck

克勞修斯

凱爾文-普朗克完美冷凍機(jī)完美熱引擎實(shí)在的熱引擎PerfectrefrigeratorPerf

Carnotengineismostefficient

卡諾引擎效率最高eCarnot=thermodynamicefficiency

熱力效率eCarnot

erev>eirrevCarnotrefrigerator卡諾冷凍機(jī),e=60%Hypotheticalengine

假想引擎,e=70%完美熱引擎Carnotengineismostef19.3.Applicationsofthe2ndLaw第二定律的應(yīng)用Powerplant發(fā)電廠fossil-fuel化石燃料:Th=650K

Nuclear核能:Th=570K

Tc=310KActualvalues實(shí)在數(shù)值:efossil~40% enuclear

~34% ecar~20%Prob54&55Heatsource熱源Boiler鍋爐Turbine渦輪機(jī)Generator發(fā)電機(jī)Electricity電Condenser冷凝器Wastewater廢水Coolingwater冷卻用水溫度溫度溫度水蒸氣水入出19.3.Applicationsofthe2ndApplication:Combined-CyclePowerPlant

應(yīng)用:聯(lián)合-循環(huán)發(fā)電廠Turbineengines:highTh(1000K2000K)&Tc(800K)…notefficient.渦輪機(jī):高Th(1000K2000K)&Tc(800K)…無(wú)効率。Steamengines:Tc~ambient300K.蒸氣機(jī):Tc~周圍的300K.Combined-cycle聯(lián)合-循環(huán):Th(1000K2000K)&Tc(300K)…e~60%Application:Combined-CyclePExample19.2.Combined-CyclePowerPlant

聯(lián)合-循環(huán)發(fā)電廠Thegasturbineinacombined-cyclepowerplantoperatesat1450C.一個(gè)聯(lián)合-循環(huán)發(fā)電廠內(nèi)的氣渦輪機(jī)在1450C下運(yùn)作。Itswasteheatat500Cistheinputforaconventionalsteamcycle,withitscondenserat8C.它的500C廢熱輸入另一個(gè)冷凝器在8C的傳統(tǒng)蒸氣循環(huán)。Findeofthecombined-cycle,&compareitwiththoseoftheindividualcomponents.求此聯(lián)合-循環(huán)的e，並與其個(gè)別組件的值比較。氣渦輪機(jī)燃燒溫度氣渦輪機(jī)蒸氣循環(huán)中介溫度冷卻水溫度Example19.2.Combined-CycleRefrigerators冷凍機(jī)Coefficientofperformance(COP)forrefrigerators:冷凍機(jī)的績(jī)效系數(shù)COPishighifTh

Tc.Th

Tc時(shí)COP高M(jìn)ax.theoreticalvalue(Carnotcycle)理論最大值(卡諾循環(huán))1stlawW=0(COP=)formovingQwhenTh

=Tc.若Th

=Tc

，移動(dòng)Q時(shí)W=0(COP=)。Refrigerators冷凍機(jī)CoefficientoExample19.3.HomeFreezer家用冰箱AtypicalhomefreezeroperatesbetweenTc=18CtoTh=30C.家用冰箱通常都在Tc=18C到Th=30C之間運(yùn)作。What’sitsmaximumpossibleCOP? 它可能的最大COP值為何？WiththisCOP,howmuchelectricalenergywouldittaketofreeze500gofwaterinitiallyat0C?在這COP值之下，需要多少電能才可以把500g在0C的水凝固？Table17.12ndlaw:onlyafractionofQcanbecomeWinheatengines.第二定律：熱引擎中祇有一部份Q能變成W。 alittleWcanmovealotofQinrefrigerators.

冷凍機(jī)內(nèi)一點(diǎn)W可以產(chǎn)生很多Q。Example19.3.HomeFreezerHeatPumps熱泵HeatpumpasAC:以熱泵作冷氣機(jī)Heatpumpasheater:以熱泵作暖爐Groundtemp~10Cyearround土地溫度整年都~10CHeatpump:movesheatfromTctoTh.HeatPumps熱泵HeatpumpasAGOTIT?19.2.AcleverengineerdecidestoincreasetheefficiencyofaCarnotenginebycoolingthelow-TreservoirusingarefrigeratorwiththemaximumpossibleCOP.一個(gè)聰明的工程師決定要提高卡諾引擎的効率，方法是用一部具有最大COP可能值的冷凍機(jī)來冷卻低溫?zé)釒?kù)。Willtheoverallefficiencyofthissystem這系統(tǒng)的整體效率會(huì)exceed 超過，belessthan 低於，equalthatof 等於theoriginalenginealone 原來引擎本身的值？seeProb32forproof證明可參考Prob32GOTIT?19.2.Acleverenginee19.4.Entropy&EnergyQuality 熵和能量品質(zhì)EnergyqualityQmeasurestheversatilityofdifferentenergyforms.能量品質(zhì)

Q衡量各種能量的可用性。2ndlaw:Energyofhigherqualitycanbeconvertedcompletelyintolowerqualityform.第二定律：高質(zhì)能量可以完全變成較低質(zhì)能量Butnotviceversa.反之卻不成。最高質(zhì)最低質(zhì)機(jī)械，電能高溫低溫19.4.Entropy&EnergyQualityConceptualExample19.1.EnergyQuality,EndUse,&Cogeneration

能量品質(zhì)，終端使用，和共發(fā)電Youneedanewwaterheater,&you’retryingtodecidebetweengas&electric.你需要一個(gè)新的熱水器；現(xiàn)正在瓦斯和電熱兩者之間作一選擇。Thegasheateris85%efficient,meaning85%ofthefuelenergygoesintoheatingwater.瓦斯熱水器的効率是85%，亦即85%的燃料能可以用來熱水。Theelectricheaterisessentially100%efficient. 電熱水器的効率可說是100%。Thermodynamically,whichheatermakesthemostsense? 從熱力學(xué)來看，那一個(gè)熱水器比較值得用?Cogeneration共發(fā)電:WasteheatfromelectricitygenerationusedforlowQneeds.發(fā)電時(shí)產(chǎn)生的廢熱用在低Q的需求上。Ans. 答Only1/3offuelenergyisconvertedtoelectricityatapowerplant.發(fā)電廠祗把燃料能的1/3轉(zhuǎn)成電能。Withthisinmind,thegasheaterisabetterchoice.在這考量下，瓦斯熱水器是較佳選擇。ConceptualExample19.1.EnerMakingtheConnection 連起來Iftheelectricitycomesfromamoreefficientgas-firedpowerplantwithe=48%,假設(shè)電力來自効率較佳，e=48%，的天然氣發(fā)電廠，comparethegasconsumptionofyourtwoheaterchoices.比較上述兩種熱水器的瓦斯消耗。Gasheater: 1unitoffuelenergybecomes0.85unitofheat.瓦斯熱水器: 1單位的燃料能可變成0.85單位的熱。Electricheater: 1unitoffuelenergybecomes0.48unitofelectricenergy,電熱水器: 1單位的燃料能可變成0.48單位的電能， thenbecomes0.48unitofheat.

再變成0.48單位的熱。Electricheaterconsumes0.85/0.48=1.8timesthefuelconsumedbygasheater.電熱水器消耗0.85/0.48=1.8倍瓦斯熱水器所需的燃料。MakingtheConnection 連起來IfthEntropy 熵lukewarm:can’tdoW,Q

微溫：不能作功，Q

Carnotcycle(reversibleprocesses):卡諾循環(huán)(可逆程序)Qh=heatabsorbed所吸熱Qc=heatrejected所排熱Qh,Qc=heatabsorbed 所吸熱C=anyclosedpath任何閉口路徑S=entropy

熵[S]=J/KIrreversibleprocessescan’tberepresentedbyapath.不可逆程序不能以路徑表達(dá)。等溫線體積壓力絕熱線C=Carnotcycle卡諾循環(huán)Contour=sumofCarnotcycles.路徑=所有卡諾循環(huán)之和Entropy 熵lukewarm:can’tdoW,Entropy 熵lukewarm:can’tdoW,Q

微溫：不能作功，Q

Carnotcycle(reversibleprocesses):卡諾循環(huán)(可逆程序)Qh=heatabsorbed所吸熱Qc=heatrejected所排熱Qh,Qc=heatabsorbed 所吸熱C=anyclosedpath任何閉口路徑S=entropy

熵[S]=J/KIrreversibleprocessescan’tberepresentedbyapath.不可逆程序不能以路徑表達(dá)。等溫線體積壓力絕熱線C=Carnotcycle卡諾循環(huán)Entropy 熵lukewarm:can’tdoW,Entropychangeispath-independent.熵變量與路徑無(wú)關(guān)。(Sisathermodynamicvariable)(S是一個(gè)熱力變數(shù))S=0overanyclosedpath任何閉口路徑上，S=0

S21

+

S12=0

S21

=

S21

Entropychangeispath-indepenEntropyinCarnotCycle 卡諾循環(huán)的熵Idealgas理想氣體：Adiabaticprocesses絕熱程序：Heatabsorbed:吸收的熱Heatrejected:排出的熱EntropyinCarnotCycle 卡諾循環(huán)的熵IrreversibleHeatTransfer 不可逆熱傳遞Cold&hotwatercanbemixedreversiblyusingextraheatbaths.冷和熱水可以用額外的熱庫(kù)來達(dá)成可逆性混合。Actualmixing,irreversibleprocesses原來的混合，不可逆程序reversibleprocesses可逆程序T1=somemediumT.某個(gè)中介T。T2=somemediumT.某個(gè)中介T。Irre