化工热力学授课教案ch8

Chapter8ProductionofPowerfromHeatcontent8.1Thesteampowerplant8.2Internal-CombustionEngines8.3JetEngines;RocketEnginesIntroductionFormsofenergyusedbymankindEnergyfromthesunThekineticenergyassociatedwithatmosphericwindsThepotentialenergyoftidesHydroelectricpowerThischapterisdevotedtotheanalysisofseveralcommonheat-enginecycles目的：研究循环中热、功转换的效果及其影响因素，探求提高能量转换效果的途径。内容：讨论蒸汽动力循环的热效率、功以及循环中各工质状态的变化。要求：HeatMechanicalenergyChemicalenergyoffuelsNuclearenergythesteampowerplanttheinternal-combustionengineHeatenginecombustionfission掌握工作原理、工质状态变化、能量转换计算、能量转换效果热力学分析。8.1ThesteampowerplantHistoryReviewCarnotcycleTSdiagramofcarnotcycleCarnotcycleismadeupoffourstepsStep1-2：ReversibleisothermalevaporationprocessStep2-3：ReversibleadiabaticexpansionprocessStep3-4：ReversibleisothermalcondensionprocessStep4-1：ReversibleadiabaticcompressionprocessCarnot’sTheoremFortwogivenheatreservoirsnoenginecanhaveathermalefficiencyhigherthanthatofaCarnotengine.3214TSTHTcCarnotefficiency1CHHWTQT8.1.1Carnot-enginecycleforsteamEquipmentsBoilerTurbineCondenserPump:ProcessesSteamgeneratedinaboilerisexpandedinanadiabaticturbinetoproducework.Thedischargesteamfromtheturbinepassestoacondenserfromwhichitispumpedadiabaticallybacktotheboiler.TSdiagramandstepsBoilerCondenserturbineHQ(turbine)SWCQ(pump)SW3142Step1-2：IsothermalevaporationprocessintheboilerStep2-3：ReversibleadiabaticexpansionprocessintheturbineStep3-4：IsothermalpartialcondensionincondenserStep4-1：ReversibleadiabaticcompressionprocessbythepumpAnalysisforwholesystem2()2suHgzmQW0sQW()()sssWWturbineWpumpHCQQQ()()sssHCWWturbineWpumpQQEfficiency1CHHWTQTPracticaldifficultiesattendtheoperationofequipment（1）湿蒸汽对汽轮机有侵蚀作用；14TS32TCTH0（2）绝热压缩过程难以实现；（3）蒸气比体积比液体大上千倍，设备及功耗大；（4）上限温度受制于临界温度，热效率不高。8.1.2RankinecycleTThheerreeaassoonnffoorriinnttrroodduucciinnggtthheeRRaannkkiinneeCCyyccllee??EquipmentsBoilerTurbineCondenserPumpStepsandTSdiagramBoilerCondenserturbineHQ(turbine)SWCQ(pump)SW3142Step1-2：Aconstant-pressureheatingprocessinaboilerStep2-3：ReversibleadiabaticexpansionofvaporinaturbineStep3-4：Aconstant-pressure,constant-temperatureprocessinacondenserStep4-1：Reversibleadiabaticpumpingofthesaturatedliquidtothepressureoftheboiler,producingcompressedliquidThedifferencesbetweenTheRankineCycleandTheCarnotCycleTTwwoommaajjoorrrreessppeeccttssTheCarnotCycleTS1432TS1432TCTHTheRankineCycleThePraticalRankineCycleDuetoirreversibilities,forstep2→3，4→1，thelinesarenolongervertical,buttendinthedirectionofincreasingentropyAnalysisforthePraticalRankineCycle2()2suHgzmQW0sQW()()sssWWturbineWpumpHCQQQ()()sssHCWWturbineWpumpQQThermodynamicCalculationforTheRankineCycleTS1432141′ST3′320Onthebasisofaunitmassoffluid21HHQHH32(turbine)()SRSHWHHH14(pump)SRHWHH43CHQHH22suHgzQWThermodynamicCalculationforTheSimplePracticalCycleOnthebasisofaunitmassoffluid21HHQHH32(turbine)sHWHH14(pump)sHWHH43CHQHH22suHgzQWTS1′43′2TS143′23Turbineefficiencyorisentropicefficiency3232turbineturbineWHHWHHSsSR（）（）PumpefficiencyppumppumpWWSRS（）（）32(turbine)sWHH32(turbine)()SRSWHHH14(pump)SRWHH14(pump)sWHHSolution8.1(a)ForRankinecycleReviewandanalysisRankinecycle32(turbine)sWHH14(pump)sWHH21(bolier)QHHThermalefficiency（循环热效率）HWQs()()WRankineQboilerss()()()WturbineWpumpQboilerSSC（汽耗率）TS143′21′3Review？11SSSCkgkJWT2P2223391.66.6858HS326.6858SSSteamwiththisentropyat10kPaiswet33333()lvlSSxSS330.64938.1511lvSS30.8047x33333()lvlHHxHH33191.82584.8lvHH32117HAnalysisp4=10kPasaturationliquiddHSdTVdPVdP141414()PPHHVdPVPP21()3191.1QboilerHHAnalysisTS143’22222PTHS3333PTHS111PTH444PTH4191.8Hs3214()()()()()1274.28.71265.5ssWRankineWturbineWpumpHHHHs()1265.50.3966()3191.1WRankineQboiler(b)ForpracticalRankinecycleReviewandanalysisturbineefficiencyWturbineWturbineSsSR（）（）WturbineWturbineSsSR（）（）pumpefficiencypWpumpWpumpSRS（）（）pWpumpWpumpSRS（）（）21()QbolierHHAnalysis32(turbine)(0.751274.50.75955.6sWHH）14()8.7(pump)11.60.750.75sHHWs()()()955.611.6944.0ssWRankineWturbineWpump14(pump)191.811.6203.4sHHWAnalysis？21(bolier)3391.6203.43188.2QHHs()944.00.2961()3188.2WRankineQboiler(c)Forapowerratingof80000kW()()ssWnetmWnet-1()8000084.75()944.0ssWnetmkgsWnet51()()84.753188.22.70210QboilermQboilerkJs43()191.82436.02244.2QcondenserHHAnalysis5-1()()84.75(2244.2)1.90210QcondensermQcondenserkgs8.1.3ModificationoftheRankineCycle朗肯循环中，等温放热、等熵膨胀和等熵压缩过程基本上能够与卡诺循环相符合，差别最大的过程是吸热过程。关键是使吸热过程向卡诺循环靠近，以提高热效率。措施：提高蒸汽的过热温度提高蒸汽压力改善循环方式等方法(1)Toincreasethevaporizationtemperature在相同的蒸汽压力下，提高蒸汽的过热温度,可提高平均吸热温度，增大作功量，提高循环的热效率，并且可以降低汽耗率乏气的干度增加，使透平机的相对内部效率也可提高。但蒸汽最高温度受到金属材料性能的限制，不能无限提高(2)Toincreasethevaporizationpressure当蒸汽压力提高时，热效率提高、而汽耗率下降。随着压力提高，乏汽干度下降，引起透平机相对内部效率降低．并使透平中最后几级的叶片受磨蚀，缩短寿命。蒸汽压力提高，不能超过水临界压力，且设备制造费用也会大幅上升。3TS142TS142TS1432562′5回热加热器1过热器汽轮机水泵冷凝器64Q1WS322′（3）TheRegenerativeCycle(回热循环)Waterfromthecondenser,ratherthanbeingpumueddirectlybacktotheboiler,isfirsth