1Chap9SummaryBasicconsiderations:actualcycle,idealcycle,carnotcycle,P-V,T-SReciprocatingenginesAssumptionsofgaspowercyclesTDCairstandardassumptions(空氣標(biāo)準(zhǔn)假設(shè)):1)air=idealgas,Cv=const;2)internalreversibleprocess;3)combustionheatadditionprocess;4)exhaustheatrejectionprocessSIengines-OttocycleFourstrokes：compressionstroke,expansionorpowerstroke,exhauststroke,intakestroke.

(壓縮沖程、做功（燃燒、膨脹）沖程、排氣沖程和吸氣沖程)CIengine-DieselCycleTheidealDieselcycle:1-2isentropiccompression(等熵壓縮);2-3constantPheataddition(定壓吸熱);3-4isentropicexpansion(等熵膨脹);4-1constantVheatrejection(定容放熱)Reciprocatingenginesareclassifiedas

spark-ignition(SI)engines(點(diǎn)燃式內(nèi)燃機(jī))compression-ignition(CI)engines(壓燃式內(nèi)燃機(jī))BDCStrokeBoreIntakevalveExhausevalveMEPTheidealOttocycle:

1-2isentropiccompression(等熵壓縮);2-3constantVheataddition(定容吸熱);3-4isentropicexpansion(等熵膨脹);4-1constantVheatrejection(定容放熱)1Chap9SummaryBasicconsiderat2Chap10SummaryCarnotcycleisnotasuitablemodelforvaporpowercycle,RankineCycleWaystoIncreaseη

ofRankineCycleRankincycles(朗肯循環(huán))Rankinecycle:1-2Isentropiccompression(pump);2-3ConstPheataddition(boiler);3-4Isentropicexpansion(turbine);4-1ConstPheatrejection(condenser)Reheatrankinecycle（再熱循環(huán)）Reheatcycle:Expandthesteamintheturbineintwostagesandreheatitinbetween.regenerativerankinecycle(回?zé)嵫h(huán))Regenerativecycle:extractingsteamfromtheturbinetoheatthefeedwaterbeforeboilerBasicidea:increaseThigh,avgforQin,anddecreaseTlow,avgforQout1,Loweringthecondenserpressure(lowerTlow,avg)2,SuperheatingthesteamtohigherT(increaseThigh,avg)3,Increasetheboilerpressure(increaseThigh,avg)Cogeneration(熱電合供循環(huán))Cogenerationistheproductionofmorethanoneusefulformofenergy(suchasprocessheatandfromthesameenergysource2Chap10SummaryCarnotcycleis3Chapter10VaporPowerCycles(蒸汽動(dòng)力循環(huán))3Chapter10VaporPowerCycles4Steamisthemostcommonworkingfluidusedinvaporpowercyclesbecauseofitsmanydesirablecharacteristics:lowcost,availability,andhighhfg.Thischapterismostlydevotedtothediscussionofsteampowerplants.Steampowerplantsarecommonlyreferredtoascoalplants,nuclearplants,ornaturalgasplants,dependingonthetypeoffuelusedtosupplyheattothesteam.Thesteamgoesthroughthesamebasiccycleinallofthem.4Steamisthemostcommonwork510-1TheCarnotVaporCycleCarnotcycleisthemostefficientcycleoperatingbetweentwospecifiedtemperaturelimits;Itwouldbeperfectifwemakeitastheidealcycleforvaporpowerplants.However,itisnotasuitablecycleforpowercycles.Considerasteady-flowcarnotcyclewithinthesaturationdomeofapuresubstance.510-1TheCarnotVaporCycleCaDomeDuomoDomeDuomo71-2:heatedinaboiler.Isothermalexpansion(等溫膨脹)

2-3:expandedinaturbine.Adiabaticexpansion(定熵膨脹)；3-4:condensedinacondenser.Isothermalcompression(等溫壓縮).4-1:compressedinacompressor.Adiabaticcompression(絕熱壓縮).Severalimpracticalitiesinthiscycle(a)For1-2and3-4,isothermalprocessareeasytoachievebykeepthemaconstantP.But,thisisonlyapplicablefortwophasesystems,andMAXTHis373.95℃forwater.2-3isentropicisclosetoawell-designedturbine.Butqualityofsteamisdecreasingduring2-3.Lowquality(highmoistureisbadforturbineblades,becauseoferosionproblem)4-1involvescompressionofliquid-vaportoasaturatedliquid.Itisnotpracticaltodesignacompressorthathandlestwophases.71-2:heatedinaboiler.Isot8Foracarnotcyclelike(b),problemsare:4-1Isentropiccompressiontoextremelyhighpressures1-2isothermalheattransferatvariablepressures.So,weconcludethat:theCarnotcyclecannotbeapproximatedinactualdevicesandisnotarealisticmodelforvaporpowercycles.8Foracarnotcyclelike(b),p910-2Rankinecycle:theidealcycleforvaporpowercyclesRankinecycle（朗肯循環(huán)）

istheidealcycleforvaporpowercycles.Itdoesnotinvolveanyinternalirreversibilitiesandconsistsoffourprocesses.1-2Isentropiccompressioninapump2-3Constantpressureheatadditioninaboiler3-4Isentropicexpansioninaturbine4-1Constantpressureheatrejectioninacondenser910-2Rankinecycle:theideal101-2Isentropiccompressioninapump(泵，等熵壓縮)2-3ConstantPheatadditioninaboiler(鍋爐，定壓加熱)3-4Isentropicexpansioninaturbine(汽輪機(jī)，等熵膨脹)4-1ConstantPheatrejectioninacondenser(冷凝器，定壓放熱)飽和水過冷水過熱蒸汽濕飽和蒸汽101-2Isentropiccompressioni11EnergyAnalysisoftheIdealRankineCycleAllfourcomponentsassociatedwiththeRankinecycle(thepump,boiler,turbine,andcondenser)aresteady-flowdevicesRankinecyclecanbeanalyzedassteady-flowprocesses.Thekineticandpotentialenergychangesofthesteamareusuallysmallandcanbeneglected.So,steady-flowenergyequationperunitmassofthesteamis11EnergyAnalysisoftheIdeal121-2:Pump(q=0)2-3:Boiler(w=0)3-4:Turbine(q=0)4-1:condenser(w=0)ThermalefficiencyEnergyAnalysisoftheIdealRankineCycle121-2:Pump(q=0)EnergyAnalysi13State1:P1,satliquidh1,v1State2:P2,s2=s1

h2State3:P3,T3h3,s3State4:P4,satMix,s4=s3h4Known:P1=P4=75kPa;P2=P3=3MPa,T3=350℃=0.2613State1:P1,satliquid1410-4Howcanweincreasetheefficiencyoftherankinecycle?Thebasicideaofallthemodificationstoincreasethethermalefficiencyofapowercycleisthesame:Increasetheaveragetemperature

atwhichheatistransferredtotheworkingfluidintheboiler(heataddition),ordecreasetheaveragetemperature

atwhichheatisrejectedfromtheworkingfluidinthecondenser(heatrejection).1410-4Howcanweincreasethe1510-4Howcanweincreasetheefficiencyoftherankinecycle?1.Loweringthecondenserpressure(lowerTlow,avg)Loweringthecondenserpressurelowersthetemperatureofsteam,andthusthetemperatureatwhichheatisrejected.1510-4Howcanweincreasethe1610-4Howcanweincreasetheefficiencyoftherankinecycle?1.Loweringthecondenserpressure(lowerTlow,avg)Effects:

(redforpositive,bluefornegative)Increasethenetworkoutput.Area1-4-4’-1’-2’-2-1.Increaseheatinputalso.Areaunder2’-2.Thermalefficiencyofcycleisincreased.Increasethemoisturecontentofsteaminturbine,whichwoulderodestheblades.x4’<x4(canbecorrected)ThereisalowerlimitforthisP:thePsatcorrespondingtoTofthecoolingmedium.P≥Psat@(Tsat=Triver+△T).E.g:Triver=15℃,△T=10℃,P≥

Psat@(Tsat=25℃)=3.2KPaAirleakageintothecondenser.1610-4Howcanweincreasethe1710-4Howcanweincreasetheefficiencyoftherankinecycle?2.SuperheatingthesteamtohigherT(increaseThigh,avg)SuperheatingthesteamtohighTincreasetheTofsteam,andthusthetemperatureatwhichheatisabsorbed.1710-4Howcanweincreasethe1810-4Howcanweincreasetheefficiencyoftherankinecycle?2.SuperheatingthesteamtohigherT(increaseThigh,avg)Effects:

(redforpositive,bluefornegative)Increasethenetworkoutput.Area3-3’-4-4’-3.Increaseheatinputalso.Areaunder3-3’Thermalefficiencyofcycleisincreasedasoveralleffectdecreasethemoisturecontentofsteaminturbine.x4’>x4ThereisalimitforthisT,becauseofmetallurgicalproblem.Current,thehighestTsteamatturbineinletis620℃.ToimproveorreplacethematerialsisonewaytoincreasethisTsteam.Likeusingceramics.1810-4Howcanweincreasethe1910-4Howcanweincreasetheefficiencyoftherankinecycle?3.Increasetheboilerpressure(increaseThigh,avg)Increasingtheoperatingpressureoftheboilerisanotherwayofincreasingtheaveragetemperatureduringtheheatadditionprocess.1910-4Howcanweincreasethe2010-4Howcanweincreasetheefficiencyoftherankinecycle?3.Increasetheboilerpressure(increaseThigh,avg)Effects:

(redforpositive,bluefornegative)Increaseanddecreaseofnetworkoutput.Area2-2’-3’-2andarea3-4-4’-3Increaseanddecreaseheatinput.ThermalefficiencyisincreasedasThigh,avgincreased.increasemoistureofsteaminturbine,butcanbecorrectedbyreheating.Manysteampowerplantsoperateatsupercriticalpressure(P>22.06MPa)andhavethermalefficiencisof40%.2010-4Howcanweincreasethe21212210-5theidealreheatrankinecycle(再熱循環(huán))Then,aquestionis:Howcanwetakeadvantageoftheincreasedefficienciesathigherboilerpressureswithoutfacingtheproblemofexcessivemoistureatthefinalstagesoftheturbine?“3.Increasetheboilerpressure(increaseThigh,avg)”increasesmoistureofsteaminturbineaswellasthermalefficiency2210-5theidealreheatrankin2310-5theidealreheatrankinecycle(再熱循環(huán))Twopossibilitiescometomind:1.Superheatthesteamtoveryhightemperaturesbeforeitenterstheturbine.Butthisisnotaviablesolution,sinceitrequiresraisingthesteamtemperaturetometallurgicallyunsafelevels.2.Expandthesteamintheturbineintwostages,andreheatitinbetween.Inotherwords,modifythesimpleidealRankinecyclewithareheatprocess.itisapracticalsolutiontothemoistureprobleminturbines,andiscommonlyusedinmodernsteampowerplants2310-5theidealreheatrankin2410-5theidealreheatrankinecycle(再熱循環(huán))Intheidealreheatrankinecycle,theexpansionprocesstakesplaceintwostagesFirststage(highpressureturbine),steamisexpandedisentropicallytoanintermediatepressureandsentbacktotheboilertobereheatedatconstantpressure,untilreachtheinletToffirstturbinestage.Secondstage(lowpressureturbine)steamisexpandedisentropicallytothecondenserpressure.2410-5theidealreheatrankin2510-5theidealreheatrankinecycle(再熱循環(huán))Effects:theincorporationofsinglereheatinapowerplantimprovesthecycleefficiencyby4-5%.(Thigh,avgisincreased)Decreasethemoistureofthesteaminturbine.Morethan2reheatisnotpracticalbecause:Efficiencyimprovementgainedby2ndreheatisonlyhalfof1stone;butcausePturbinedecreaseandsuperheatedexhaustthenTlow,avgincrease.AddedcostandcomplexityDoublereheatisonlyusedonsupercriticalpressurepowerplants.IfmaterialscouldwithstandsufficientlyhighT,reheatcycleisnotnecessary.

2510-5theidealreheatrankin2610-6theidealregenerativerankinecycle(回?zé)嵫h(huán))InT-sdiagramoftheRankinecycle,heattransferduringprocess2-2’isfoundatarelativelylowT,solowercycleefficiency;raiseToftheliquidleavingthepumpbeforetheboilerisonesolution;Apracticalprocess(regeneration,回?zé)?isaccomplishedbyextractingsteamfromtheturbineatvariouspointsandheatthefeedwaterbeforetheboiler.Thedevicewherethefeedwaterisheatedbyregenerationiscalledaregenerator(回?zé)崞?,orfeedwaterheater（給水加熱器）.2610-6theidealregenerative2710-6theidealregenerativerankinecycle(回?zé)嵫h(huán))Effectsofregeneration:Improvecycleefficiency.Provideaconvenientmeansofdeaerating(除氣)thefeedwaterandpreventcorrosionintheboiler.Controlthelargevolumeflowrateofthesteamatthefinalstagesoftheturbine(duetolargespecificvolumesatlowpressures)Regenerationhasbeenusedinallmodernsteampowerplantssince1920s.thefeedwatercouldbeheatedbymixingwithsteam(openfeedwaterheaters)orwithoutmixing(closedfeedwaterheaters)2710-6theidealregenerative2810-6theidealregenerativerankinecycle(回?zé)嵫h(huán))Anopen(ordirect-contact)feedwaterheaterisbasicallyamixingchamber,wherethesteamextractedfromtheturbinemixeswiththefeedwaterexitingthepump.2810-6theidealregenerative2910-6theidealregenerativerankinecycle(回?zé)嵫h(huán))Intheclosedfeedwaterheater,heatistransferredfromtheextractedsteamtothefeedwaterwithoutanymixingtakingplace.Thetwostreamscanbeatdifferentpressures,sincetheydonotmix.2910-6theidealregenerative3010-6theidealregenerativerankincycle(回?zé)嵫h(huán))ComparisonOpenfeedwaterheaters

aresimpleandinexpensivehavegoodheattransfercharacteristics.Theybringthefeedwatertothesaturationstate.Foreachheater,however,apumpisrequiredtohandlethefeedwater.

Theclosedfeedwaterheaters

morecomplexbecauseoftheinternaltubingnetwork,andmoreexpensive.Heattransferislesseffectivesincethetwostreamsarenotallowedtobeindirectcontact.However,closedfeedwaterheatersdonotrequireaseparatepumpforeachheatersincetheextractedsteamandthefeedwatercanbeatdifferentP3010-6theidealregenerative10-6theidealregenerativerankinecycle(回?zé)嵫h(huán))Moststeampowerplantsuseacombinationofopenandclosedfeedwaterheaters.3110-6theidealregenerativera3210-8Cogeneration(熱電合共循環(huán))Ingeneral,

cogeneration

istheproductionofmorethanoneusefulformofenergy(suchasprocessheatandelectricpower)fromthesameenergysource.Anidealcogenerationplant:120KWenergyisinputtotheboiler,20KWpowerisproducedinturbine,100KWheatissuppliedasprocessheat.Utilizationfactor(熱量利用系數(shù)):3210-8Cogeneration(熱電合共循環(huán))In3310-8Cogeneration(熱電合共循環(huán))Anidealcogenerationplantisnotpracticalsincethepowerandprocess-heatisnotadjustable.Andamorepracticalcogenerationplantisshowninfig10-22.Cogenerationplants(熱電廠)haveprovedtobeeconomicallyveryattractive.Moreandmorehavebeeninstalledandarebeinginstalled.Especiallyindistrictheating(區(qū)域集中供熱).3310-8Cogeneration(熱電合共循環(huán))An10-310-710-9自學(xué)10-335Chap10SummaryCarnotcycleisnotasuitablemodelforvaporpowercycle,RankineCycleWaystoIncreaseη

ofRankineCycleRankinecycles(朗肯循環(huán))Rankinecycle:1-2Isentropiccompression(pump);2-3ConstPheataddition(boiler);3-4Isentropicexpansion(turbine);4-1ConstPheatrejection(condenser)Reheatrankinecycle（再熱循環(huán)）Reheatcycle:Expandthesteamintheturbineintwostagesandreheatitinbetween.regenerativerankinecycle(回?zé)嵫h(huán))Regenerativecycle:extractingsteamfromtheturbinetoheatthefeedwaterbeforeboilerBasicidea:increaseThigh,avgforQin,anddecreaseTlow,avgforQout1,Loweringthecondenserpressure(lowerTlow,avg)2,SuperheatingthesteamtohigherT(increaseThigh,avg)3,Increasetheboilerpressure(increaseThigh,avg)Cogeneration(熱電合供循環(huán))Cogenerationistheproductionofmorethanoneusefulformofenergy(suchasprocessheatandfromthesameenergysource35Chap10SummaryCarnotcyclei3610-1C10-2C10-7C10-8C10-9C10-10C10-12C

10-29C10-30C10-39C10-40C3610-1C37Chap9SummaryBasicconsiderations:actualcycle,idealcycle,carnotcycle,P-V,T-SReciprocatingenginesAssumptionsofgaspowercyclesTDCairstandardassumptions(空氣標(biāo)準(zhǔn)假設(shè)):1)air=idealgas,Cv=const;2)internalreversibleprocess;3)combustionheatadditionprocess;4)exhaustheatrejectionprocessSIengines-OttocycleFourstrokes：compressionstroke,expansionorpowerstroke,exhauststroke,intakestroke.

(壓縮沖程、做功（燃燒、膨脹）沖程、排氣沖程和吸氣沖程)CIengine-DieselCycleTheidealDieselcycle:1-2isentropiccompression(等熵壓縮);2-3constantPheataddition(定壓吸熱);3-4isentropicexpansion(等熵膨脹);4-1constantVheatrejection(定容放熱)Reciprocatingenginesareclassifiedas

spark-ignition(SI)engines(點(diǎn)燃式內(nèi)燃機(jī))compression-ignition(CI)engines(壓燃式內(nèi)燃機(jī))BDCStrokeBoreIntakevalveExhausevalveMEPTheidealOttocycle:

1-2isentropiccompression(等熵壓縮);2-3constantVheataddition(定容吸熱);3-4isentropicexpansion(等熵膨脹);4-1constantVheatrejection(定容放熱)1Chap9SummaryBasicconsiderat38Chap10SummaryCarnotcycleisnotasuitablemodelforvaporpowercycle,RankineCycleWaystoIncreaseη

ofRankineCycleRankincycles(朗肯循環(huán))Rankinecycle:1-2Isentropiccompression(pump);2-3ConstPheataddition(boiler);3-4Isentropicexpansion(turbine);4-1ConstPheatrejection(condenser)Reheatrankinecycle（再熱循環(huán)）Reheatcycle:Expandthesteamintheturbineintwostagesandreheatitinbetween.regenerativerankinecycle(回?zé)嵫h(huán))Regenerativecycle:extractingsteamfromtheturbinetoheatthefeedwaterbeforeboilerBasicidea:increaseThigh,avgforQin,anddecreaseTlow,avgforQout1,Loweringthecondenserpressure(lowerTlow,avg)2,SuperheatingthesteamtohigherT(increaseThigh,avg)3,Increasetheboilerpressure(increaseThigh,avg)Cogeneration(熱電合供循環(huán))Cogenerationistheproductionofmorethanoneusefulformofenergy(suchasprocessheatandfromthesameenergysource2Chap10SummaryCarnotcycleis39Chapter10VaporPowerCycles(蒸汽動(dòng)力循環(huán))3Chapter10VaporPowerCycles40Steamisthemostcommonworkingfluidusedinvaporpowercyclesbecauseofitsmanydesirablecharacteristics:lowcost,availability,andhighhfg.Thischapterismostlydevotedtothediscussionofsteampowerplants.Steampowerplantsarecommonlyreferredtoascoalplants,nuclearplants,ornaturalgasplants,dependingonthetypeoffuelusedtosupplyheattothesteam.Thesteamgoesthroughthesamebasiccycleinallofthem.4Steamisthemostcommonwork4110-1TheCarnotVaporCycleCarnotcycleisthemostefficientcycleoperatingbetweentwospecifiedtemperaturelimits;Itwouldbeperfectifwemakeitastheidealcycleforvaporpowerplants.However,itisnotasuitablecycleforpowercycles.Considerasteady-flowcarnotcyclewithinthesaturationdomeofapuresubstance.510-1TheCarnotVaporCycleCaDomeDuomoDomeDuomo431-2:heatedinaboiler.Isothermalexpansion(等溫膨脹)

2-3:expandedinaturbine.Adiabaticexpansion(定熵膨脹)；3-4:condensedinacondenser.Isothermalcompression(等溫壓縮).4-1:compressedinacompressor.Adiabaticcompression(絕熱壓縮).Severalimpracticalitiesinthiscycle(a)For1-2and3-4,isothermalprocessareeasytoachievebykeepthemaconstantP.But,thisisonlyapplicablefortwophasesystems,andMAXTHis373.95℃forwater.2-3isentropicisclosetoawell-designedturbine.Butqualityofsteamisdecreasingduring2-3.Lowquality(highmoistureisbadforturbineblades,becauseoferosionproblem)4-1involvescompressionofliquid-vaportoasaturatedliquid.Itisnotpracticaltodesignacompressorthathandlestwophases.71-2:heatedinaboiler.Isot44Foracarnotcyclelike(b),problemsare:4-1Isentropiccompressiontoextremelyhighpressures1-2isothermalheattransferatvariablepressures.So,weconcludethat:theCarnotcyclecannotbeapproximatedinactualdevicesandisnotarealisticmodelforvaporpowercycles.8Foracarnotcyclelike(b),p4510-2Rankinecycle:theidealcycleforvaporpowercyclesRankinecycle（朗肯循環(huán)）

istheidealcycleforvaporpowercycles.Itdoesnotinvolveanyinternalirreversibilitiesandconsistsoffourprocesses.1-2Isentropiccompressioninapump2-3Constantpressureheatadditioninaboiler3-4Isentropicexpansioninaturbine4-1Constantpressureheatrejectioninacondenser910-2Rankinecycle:theideal461-2Isentropiccompressioninapump(泵，等熵壓縮)2-3ConstantPheatadditioninaboiler(鍋爐，定壓加熱)3-4Isentropicexpansioninaturbine(汽輪機(jī)，等熵膨脹)4-1ConstantPheatrejectioninacondenser(冷凝器，定壓放熱)飽和水過冷水過熱蒸汽濕飽和蒸汽101-2Isentropiccompressioni47EnergyAnalysisoftheIdealRankineCycleAllfourcomponentsassociatedwiththeRankinecycle(thepump,boiler,turbine,andcondenser)aresteady-flowdevicesRankinecyclecanbeanalyzedassteady-flowprocesses.Thekineticandpotentialenergychangesofthesteamareusuallysmallandcanbeneglected.So,steady-flowenergyequationperunitmassofthesteamis11EnergyAnalysisoftheIdeal481-2:Pump(q=0)2-3:Boiler(w=0)3-4:Turbine(q=0)4-1:condenser(w=0)ThermalefficiencyEnergyAnalysisoftheIdealRankineCycle121-2:Pump(q=0)EnergyAnalysi49State1:P1,satliquidh1,v1State2:P2,s2=s1

h2State3:P3,T3h3,s3State4:P4,satMix,s4=s3h4Known:P1=P4=75kPa;P2=P3=3MPa,T3=350℃=0.2613State1:P1,satliquid5010-4Howcanweincreasetheefficiencyoftherankinecycle?Thebasicideaofallthemodificationstoincreasethethermalefficiencyofapowercycleisthesame:Increasetheaveragetemperature

atwhichheatistransferredtotheworkingfluidintheboiler(heataddition),ordecreasetheaveragetemperature

atwhichheatisrejectedfromtheworkingfluidinthecondenser(heatrejection).1410-4Howcanweincreasethe5110-4Howcanweincreasetheefficiencyoftherankinecycle?1.Loweringthecondenserpressure(lowerTlow,avg)Loweringthecondenserpressurelowersthetemperatureofsteam,andthusthetemperatureatwhichheatisrejected.1510-4Howcanweincreasethe5210-4Howcanweincreasetheefficiencyoftherankinecycle?1.Loweringthecondenserpressure(lowerTlow,avg)Effects:

(redforpositive,bluefornegative)Increasethenetworkoutput.Area1-4-4’-1’-2’-2-1.Increaseheatinputalso.Areaunder2’-2.Thermalefficiencyofcycleisincreased.Increasethemoisturecontentofsteaminturbine,whichwoulderodestheblades.x4’<x4(canbecorrected)ThereisalowerlimitforthisP:thePsatcorrespondingtoTofthecoolingmedium.P≥Psat@(Tsat=Triver+△T).E.g:Triver=15℃,△T=10℃,P≥

Psat@(Tsat=25℃)=3.2KPaAirleakageintothecondenser.1610-4Howcanweincreasethe5310-4Howcanweincreasetheefficiencyoftherankinecycle?2.SuperheatingthesteamtohigherT(increaseThigh,avg)SuperheatingthesteamtohighTincreasetheTofsteam,andthusthetemperatureatwhichheatisabsorbed.1710-4Howcanweincreasethe5410-4Howcanweincreasetheefficiencyoftherankinecycle?2.SuperheatingthesteamtohigherT(increaseThigh,avg)Effects:

(redforpositive,bluefornegative)Increasethenetworkoutput.Area3-3’-4-4’-3.Increaseheatinputalso.Areaunder3-3’Thermalefficiencyofcycleisincreasedasoveralleffectdecreasethemoisturecontentofsteaminturbine.x4’>x4ThereisalimitforthisT,becauseofmetallurgicalproblem.Current,thehighestTsteamatturbineinletis620℃.ToimproveorreplacethematerialsisonewaytoincreasethisTsteam.Likeusingceramics.1810-4Howcanweincreasethe5510-4Howcanweincreasetheefficiencyoftherankinecycle?3.Increasetheboilerpressure(increaseThigh,avg)Increasingtheoperatingpressureoftheboilerisanotherwayofincreasingtheaveragetemperatureduringtheheatadditionprocess.1910-4Howcanweincreasethe5610-4Howcanweincreasetheefficiencyoftherankinecycle?3.Increasetheboilerpressure(increaseThigh,avg)Effects:

(redforpositive,bluefornegative)Increaseanddecreaseofnetworkoutput.Area2-2’-3’-2andarea3-4-4’-3Increaseanddecreaseheatinput.ThermalefficiencyisincreasedasThigh,avgincreased.increasemoistureofsteaminturbine,butcanbecorrectedbyreheating.Manysteampowerplantsoperateatsupercriticalpressure(P>22.06MPa)andhavethermalefficiencisof40%.2010-4Howcanweincreasethe57215810-5theidealreheatrankinecycle(再熱循環(huán))Then,aquestionis:Howcanwetakeadvantageoftheincreasedefficienciesathigherboilerpressureswithoutfacingtheproblemofexcessivemoistureatthefinalstagesoftheturbine?“3.Increasetheboilerpressure(increaseThigh,avg)”increasesmoistureofsteaminturbineaswellasthermalefficiency2210-5theidealreheatrankin5910-5theidealreheatrankinecycle(再熱循環(huán))Twopossibilitiescometomind:1.Superheatthesteamtoveryhightemperaturesbeforeitenterstheturbine.Butthisisnotaviablesolution,sinceitrequiresraisingthesteamtemperaturetometallurgicallyunsafelevels.2.Expandthesteamintheturbineintwostages,andreheatitinbetween.Inotherwords,modifythesimpleidealRankinecyclewithareheatprocess.itisapracticalsolutiontothemoistureprobleminturbines,andiscommonlyusedinmodernsteampowerplants2310-5theidealreheatrankin6010-5theidealreheatrankinecycle(再熱循環(huán))Intheidealreheatrankinecycle,theexpansionprocesstakesplaceintwostagesFirststage(highpressureturbine),steamisexpandedisentropicallytoanintermediatepressureandsentbacktotheboilertobereheatedatconstantpressure,untilreachtheinletToffirstturbinestage.Secondstage(lowpressureturbine)steamisexpandedisentropicallytothecondenserpressure.2410-5theidealreheatrankin6110-5theidealreheatrankinecycle(再熱循環(huán))Effects:theincorporationofsinglereheatinapowerplantimprovesthecycleefficiencyby4-5%.(Thigh,avgisincreased)Decreasethemoistureofthesteaminturbine.Morethan2reheatisnotpracticalbecause:Efficiencyimprovementgainedby2ndreheatisonlyhalfof1stone;butcausePturbinedecreaseandsuperheatedexhaustthenTlow,avgincrease.AddedcostandcomplexityDoublereheatisonlyusedonsupercriticalpressurepowerplants.IfmaterialscouldwithstandsufficientlyhighT,reheatcycleisnotnecessary.

2510-5theidealreheatrankin6210-6theidealregenerativerankinecycle(回?zé)嵫h(huán))InT-sdiagramoftheRankinecycle,heattransferduringprocess2-2’isfoundatarelativelylowT,solowercycleefficiency;raiseToftheliquidleavingthepumpbeforetheboilerisonesolution;Apracticalprocess(regeneration,回?zé)?isaccomplishedbyextractingsteamfromtheturbineatvariouspointsandheatthefeedwaterbeforetheboiler.Thedevicewherethefeedwaterisheatedbyregenerationiscalledaregenerator(回?zé)崞?,orfeedwaterheater（給水加熱器）.2610-6theidealregenerative6310-6theidealregenerativerankinecycle(回?zé)嵫h(huán))Effectsofregeneration:Improvecycleefficiency.Provideaconvenientmeansofdeaerating(除氣)thefeedwaterandpreventc