2004《工程热力学》试卷(A)

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1、工程热力学试卷（A）(120minutes)班级班级序号姓名成绩题号SectionASectionBSectionC总分得分阅卷人SectionA:Answerthefollowingquestions(8*5)1.Whatistheconditionofthefollowingequations?2.Whatisthedifferencebetweengagepressureandabsolutepressure?3.Whatisaperpetual-motionmachineofthefirstkindandwhatisaperpetual-motionmachineo

2、fthesecondkind?4.Ingasrefrigerationcycles,canwereplacetheturbinebyanexpansionvalveaswedidinvapor-compressionrefrigerationcycles?Why?5.PleaseuseaT-sdiagramtoillustratetheinfluenceofturbineinletpressuretotheefficiencyofasimpleidealRankinecycle.6.WhatfourprocessesmakeupthesimpleidealBraytoncy

3、cle?7.Howdorelativeandspecifichumilitieschangeduringasimpleheatingprocess?Answerthesamequestionforasimplecoolingprocess.1.Ifairflowsintoanozzleatanultrasonicspeed,whatkindofnozzleshouldbeused?Why?SectionB:Drawdiagramaccordingtotherequest(2*10)1.PleasedrawthefollowingcycleinaT-sdiagram.Pv12

4、345ssvpv2.Please,showtheschematicofareheatRankinecycleandindicatethenameofequipmenteach.SectionC:Calculation1.(15)Anidealgaspowercycle.Theairiscompressedadiabaticallyfromstate1(p1＝1.01bar、t1=15℃、Vl＝0.014m3)tostate2(V2=0.0028m3).Afterthis,heatedatconstantvolumetostate3(p3=18.5bar).Thenexpan

5、dadiabaticallytostate4(p4=1.01bar).Finally,theairbacktostate1atconstantpressure.Pleasecalculate:(1)Thenetworkofthiscycle.(2)Theefficiencyofthiscycle.(R=287J/kg.Kk=1.4takecp,cvasconstant)2.(10)Please,useClausuisinequalitytojudgethefollowingcycle’sdirection(engineorrefrigerator)/Q2/=3000JT2=

6、700KT1=300K/W/=1000J1.(15)AstoaregenerativeRankinecycle,theenthalpyateachpointhasbeenshowninthefollowingschematic.Ifeachfeedwaterheatergivesthesameenthalpyincreasetothefeedwaterandthepowerforpumpcanbeneglected,then:(1)Pleasederivetheexpressionofthefractionofsteamextractedforeachfeedwaterhe

7、ater.(2)TheexpressionofefficiencyTurbineinletenthalpyh1Extractionenthalpyofstage2h7Drainageenthalpyofstage1h6Feedwaterenthalpyh4Extractionenthalpyofstage1h5SteamTurbineCondenseroutletenthalpyh3Turbineexhaustenthalpyh2Boiler