制冷技术英文版Ch090528VIP免费

1Part2.ThePrinciplesofRefrigeration(116pages)Chapter2.ThermodynamicAnalysisofrefrigerationcycle2-1)TheLawsofThermodynamicsandTheirRelationtoRefrigerationThermodynamicsareprimarilyconcernedwithtwoformsofenergy:heatandwork.ThereforeEngineeringThermodynamicsisthestudyoftheinterrelationbetweenheat,work,andinternalenergy.Therearetwoimportantconceptsofthermodynamicanalysis:SystemandEnvironment.Asystem（系统、体系）isdefinedasanyquantityofmatterorregionofspacetowhichattentionisdirectedforpurposeofanalysis;andeverythingoutsidethesystemboundaryisreferredtoastheenvironment（环境）.[1,2]（1）The0thLawofThermodynamicsTheZerothLawofThermodynamicsstates:热平衡定律—温度定义1.Iftwosystemsareeachequalintemperaturetoathirdsystem,thenthetemperaturesofthetwosystemsthemselvesareequal.2.Iftwoclosedsystems(togetherisolated),withdifferenttemperaturesarebroughtintothermalcontact,thenthetemperaturesofthetwosystemswillchangetoapproachthesametemperature.Thatis,thetemperatureofthesystemwhichisatahighertemperaturewilldecreaseandthetemperatureofthesystemwiththelowertemperaturewillincrease.Theywilleventuallyhavethesametemperature.热力学第零定律的重要性在于它给出了温度的定义和温度的测量方法。定律中所说的热力学系统是指由大量分子、原子组成的物体或物体系。它为建立温度概念提供了实验基础。这个定律反映出：处在同一热平衡状态的所有的热力学系统都具有一个共同的宏观特征，这一特征是由这些互为热平衡系统的状态所决定的一个数值相等的状态函数，这个状态函数被定义为温度。而温度相等是热平衡之必要的条件。（2）The1stLawofThermodynamics---能量守恒定律Theenergyofanisolatedsystemremainsconstant.（isolatedsystem孤立体系=体系+环境）这里的环境：包括体系以外的全部—冷源、热源和做功的机械2Fig.1-2,RefrigerationandHeatPumpWithinanisolatedsystem,wherenootherenergyormaterialcanenterorleave,energycanneitherbecreatednordestroyed.Althoughenergycannotbecreatedordestroyed,itcanbetransferredtoworkotherformsofenergy.TheFirstLawofThermodynamicscanbeexpressedasamathematicalinterpretationasWdUQ(2-1)对一个循环来说，0dU012WQQ(2-2)InBritishSystemofUnits,Btu（abbr.BritishThermalUnit）isstillusedastheunitofheatandinnerenergy,whichwasdefinedasthequantityofheatrequiredtoraisethetemperatureofoneIbofwaterbyF01from63Fo.to64Fo.Thefollowingrelationsexist.joulesBtu06.10551;Btujoule410478.91(2-3)orhBtuhkcaljouleW/41214.3/859845.0sec/11CoefficientofPerformance性能系数COP,isdefinedastheratioofdesiredresulttorequiredinput.WQinputrequiredresultdesiredCOP1for“refrigerator”(2-4a)WQInputrequiredresultdesiredCOP2for“heatpump”(2-4b)ThisvaluesofCOPmaybelargerthan100%forrefrigeratororheatpump.AndCOPisexpectedtobeaslargeaspossible.（而热机的效率%100inQWinputrequiredresultdesired）（3）The2ndLawofThermodynamics---不可逆的自发过程；熵3Thereareseveralalternatebutequivalentwaystodescribethe2ndLaw:1.HeatTransfer:Heatflowsspontaneouslyfromahotbodytoacoolbodyinabsenceofothereffects,nottheopposite.2.MassTransfer:Fluidflowsspontaneouslyfromahighpressuretolowpressureinabsenceofothereffects,nottheopposite.3.Diffusion:Twogases,whenplacedinanisolatedchamber,willmixuniformlythroughoutthechamber,butwillnotseparatespontaneouslyoncemixed.以上是3种不可逆的自发过程4.3Itisimpossibletoconvertheatcompletelyintousefulwork.5.Foranisolatedsystem,anychangeovertimeofentropySiseitherpositiveorzero,thatis:熵的定义TdQdS0isolaS(2-5)Inthecasesofrefrigeratororheatpump,theheatistobetakenoutfromacold...