工程热力学--aps审核

工程热力学“工程热力学”这门课程主要介绍了热力学几个重要概念，例如压力、温度、热容、热力学能、焓、熵等，并且详细讲解了三大热力学定理以及如何计算分析能量的转化过程。热力学第一定律：“自然界中的一切物质都具有能量，能量不可能被创造，也不可能被消灭，但可以从一种形态转变为另一种形态；在能量转化过程中能量的总量保持不变。”热力学第二定律有两种表达方式：热不能自发地、不付代价地从低温物体传至高温物体；不可能制造出从单一热源吸热，使之全部转化为功而不留下其他任何变化的热力发动机。热力学第三定律：绝对零度不可能达到。卡诺循环（p-v图、T-s图），它是以绝热压缩、定温吸热、绝热膨胀和定温放热四个过程组成的，其热效率为ηt=1−T2T1，它表明了卡诺循环的热效率只决定于高温热源和低温热源的温度，并且其效率只能小于1，决不能等于1，它为提高各种热动力机的效率指明了方向。提高卡诺热机热效率的方法：尽可能提高工质的吸热温度和尽可能降低工质的放热温度。奥拓循环（定容加热理想循环p-v图、T-s图），它是以定熵压缩、定容加热、定熵膨胀和定容放热四个过程组成的，其热效率为ηt=1−1εk−1，提高奥拓循环热效率的方法：提高压缩比狄赛尔循环（定压加热理想循环p-v图、T-s图）它是以定熵压缩、定压加热、定熵膨胀和定容放热四个过程组成的。理想气体状态方程：pV=nRT⟹pv=RgT定压比热容cp、定容比热容cv：cp=dhdTcv=dUdTcp−cv=Rg焓：H=U+pV熵增：若cp恒定，△s1−2=cplnT2T1−Rglnp2p1；若cv恒定，△s1−2=cvlnT2T1+Rglnv2v1；若cp、cv均恒定△s1−2=cvlnp2p1+cplnv2v1克劳修斯不等式（热力学第二定律数学表达式）：δQTr≤0理想气体声速方程c=kpv=kRgT，马赫数Ma=cfc可逆过程工质技术功推动功闭口系统开口系统绝热系统多变过程多变指数孤立系统熵增原理EngineeringThermodynamics“Thermodynamics”mainlyintroducesussomeimportantconceptsofthermodynamics,suchaspressure,temperature,heatcapacity,thermodynamicenergy,enthalpy,entropy,etc.,andexplainsindetailwhatthethreethermodynamiclawsareandhowtocalculateandanalyzetransformationprocessoftheenergy.Firstlawofthermodynamics:Allmatterinnaturehasenergy;energycannotbecreated,cannotbedestroyedbutcanbechangedfromoneformtoanotherform;intheenergyconversionprocessthetotalamountofenergywillbemaintainedunchanged.”SecondLawofThermodynamicshastwoexpressions:“Heatcannotspontaneouslyspreadfromtheobjectoflowtemperaturetotheobjectofhightemperaturewithoutanycost”;“Itisimpossibletocreateanengine,whichcantransformtheheatfromasinglesourcetomaketheengineworkwithoutanyotherchanges.Thirdlawofthermodynamics:absolutezerocannotbeachieved.ForexampleweusetheCarnotcycle(pvdiagram,Tsdiagram)tocomprehendtheworkingprocessesofanidealengine.TheCarnotcycleiscomposedbytworeversibleconstanttemperatureprocesses(可逆定温过程)andtworeversiblethermoinsulationprocesses（可逆绝热过程）.Theworkingmedium(工质)absorbsheatfromaconstanttemperaturesourceT1andreleasesheattoanotherconstanttemperaturesourceT2.Theprocessfromdtoaisthermoinsulationcompressingprocess(绝热压缩),formatobisconstanttemperatureheatabsorbingprocess（定温吸热）,frombtocisthermoinsulationexpandingprocess（绝热膨胀）,fromctodisconstanttemperatureheatreleasingprocess(定温放热).Itsthermalefficiencyη_t=1-T_2/T_1,itshowsthattheCarnotcycleefficiencydependsonlyonhightemperatureandlowtemperatureheatsource,anditsefficiencycanonlybelessthan1,notbeequalto1.Itmakesacleardirectiontoimprovetheefficiency.TheapproachtoimprovetheefficiencyofCarnotheatengine:trytoimprovethehightemperatureanddecreasethelowtemperatureofworkingmedium.Ottocycle(idealcycle,whichheatsatconstantvolumepvdiagram,Tsdiagram),whichincludestheentropycompressionprocess,constantvolumeheatingprocess,fixedentropyheatexpansionprocessandconstantvolumeheatreleasingprocess,anditsthermalefficiencyisη_t=1-1/ε^(k-1).TheapproachtoimprovetheefficiencyofOttoheatengine:trytoimprovethecompressionratio.DiSaiercycle(idealcycle,whichheatsatconstantpressurepvdiagram,Tsdiagram),whichconsistoffixedentropycompressionprocess,constantpressureheatingprocess,fixedentropyexpansionprocessandheatatconstantvolumeprocess.Idealgasequation:pV=nRT⟹pv=R_gTspecificheatcapacityc_p,specificheatcapacityc_v:c_p=dh/dTc_v=dU/dTc_p〖-c〗_v=R_genthalpy:H=U+pVentropy:Ifc_pconstant,△s_(1-2)=c_plnT_2/T_1-R_glnp_2/p_1;ifc_vconstant,△s_(1-2)=c_vlnT_2/T_1+R_glnv_2/v_1;ifc_p,c_vareconstant△s_(1-2)=c_vlnp_2/p_1+c_plnv_2/v_1Clausiusinequality(mathematicalexpressionofthesecondlawofthermodynamics):∮▒δQ/T_r≤0Thesoundspeedoftheidealgasequationc=√kpv=√(kR_gT),MachnumberMa=c_f/c可逆过程Reversibleprocess工质workingmedium技术功Technicalwork推动功pushingwork闭口系统Closedsystem开口系统Opensystem绝热系统adiabaticsystem多变过程Polytropicprocess多变指数Polytropicexponent孤立系统熵增原理IsolatedsystementropyprincipleThezerothlawofthermodynamics,whichunderliesthebasicdefinitionoftemperature.Thefirstlawofthermodynamics,whichmandatesconservationofenergy,andstatesinparticularthattheflowofheatisaformofenergytransfer.Thesecondlawofthermodynamics,whichstatesthattheentropyofanisolatedmacroscopicsystemneverdecreases,or(equivalently)thatperpetualmotionmachinesareimpossible.Thethirdlawofthermodynamics,whichconcernstheentropyofaperfectcrystalatabsolutezerotemperature,andwhichimpliesthatitisimpossibletocoolasystemallthewaytoexactlyabsolutezero.