高等工程熱力學(xué)2熱力學(xué)第一定律第1頁(yè)/共62頁(yè)2Chapter2熱力學(xué)第一定律

TheFirstLawofThermodynamics第2頁(yè)/共62頁(yè)3SummaryaboutHistoricalDevelopmentofthe1stLaw

TheWorkLine——(Machines)The12thcentury,China→ManchesterThe13th,14th,15thcenturies:theproliferationofwater-drivenmachines,airbellows,waterpumps,irrigation,andsoon15th,16th,17th.ThetechnologyandstudyofpumpsTheuseofmathematicalanalysiswasintroducedThebarometerwasinventedbyTorricelli,1644Abasicunderstandingoftheoriginsofatmosphericpressure(Pascal,1648)Theinventionofair(vacuum)pump(Otto,1654)Thefirstatmosphericengine(Thomas,1698)第3頁(yè)/共62頁(yè)4TheConservationofForceandMethodofinfinitesimalCalculus(Leibnitz,1684,Newton,1687)TheLawofUniversalGravitation,TheNewtonThreeLawsofMotion,andGeometricCalculus(Newton,1687)TheConservationofLiveForceinHydraulics,theKinetic-molecularTheoryofGases(Bernoilli,1738)TheMathematicalFoundationsofInviscidFlowFlow(Euler,1755)TheGravitationalFieldTheoryandMathematicsofThermalDiffusion(Laplace,1785)SummaryaboutHistoricalDevelopmentofthe1stLaw

TheWorkLine

FromMechanicstoMachineScience第4頁(yè)/共62頁(yè)5TheLawGoverningFriction(Coulomb,1781)Thefoundationsofdescriptivegeometry[Monge,1795]Thebeginningsofascienceofmachines“CarnotPrinciple”,MaximumEfficiency,continuityofpower[1783]The“dynamicUnit”,W=mgh=1(kg)×9.8(m/s2)×1(m),(Hachette,1811)The“Calorie”asthequantityofheatrequiredtoraisethetemperatureof1kilogramofwaterby10C[Clement,1826]SummaryaboutHistoricalDevelopmentofthe1stLaw

TheWorkLine

FromMechanicstoMachineScience第5頁(yè)/共62頁(yè)6Galilei’sBarothermoscope[1592]Sealed-stemthermometersfilledwithalcohol[1654]Theairthermometer:avolumeofairconfinedbyacolumnofmercuryasindicator(1600s)Themercury-in-glassthermometer[Fahrenheit,1714]SummaryaboutHistoricalDevelopmentofthe1stLaw

TheHeatLine

Thermometry第6頁(yè)/共62頁(yè)7Theelasticityofagas,PV=constantatconstantT(Boyle,1660)Theconstancyoftemperatureduringphasechange(Newton,1701)Thelatentheatoffusionoficeandtheconceptofspecificheat[Wilcke,1772]4.ThegaslawV∝TatconstantP[Gay-Lussac,1802]Thelawofpartialpressureingasmixtures[Avogadro,1811]Thediscoveryofcriticaltemperature[Latour,1810s]TheapproximatecharacterofBoyle’slawforrealgases;measurementofthespecificheatandthermalexpansioncoefficient;[Regnault,mid-1800s]SummaryaboutHistoricalDevelopmentofthe1stLaw

TheHeatLine-Calorimetry第7頁(yè)/共62頁(yè)8Theproportionalitybetweencoolingrate&body-surroundingstemperaturedifference[Newton,1701]ComparativemeasurementofthermalconductivityConvectionasaprincipalheattransfermechanismthroughclothingTheproportionalitybetweenheattransferrate&temperaturegradientDistinctionbetweenthethermalconductivity&theheattransfercoefficientFourierHeatConductionFormulationSummaryaboutHistoricalDevelopmentofthe1stLaw

TheHeatTransfer第8頁(yè)/共62頁(yè)9SummaryaboutHistoricalDevelopmentofthe1stLawThe“firstlaw”asanintegralpartofthenewscienceofthermodynamics

[Clausius,1850,Rankine,1850,Kelvin,1851andlater]第9頁(yè)/共62頁(yè)10ElementsofThermodynamicsTerminologyThermodynamicdescriptionofnaturalprocessesusuallybeginsbydividingtheworldintoa“system”andits“exterior”,“surroundings”

“environment,”whichistherestoftheword.System:Collectionofmatter,regioninspace第10頁(yè)/共62頁(yè)ClosedSystems（封閉系統(tǒng)，閉口系）Masscannotcrosstheboundariesofaclosedsystem,butenergycan.Exchangingheat&mechanicalenergy,butnomatterwiththeenvironment.第11頁(yè)/共62頁(yè)12OpenSystemsThethermodynamicsystemitselfisusuallyreferredtoasthecontrolvolume,thesystemboundaryisthecontrolsurface,andtheparticularpatchesoftheboundarythatarecrossedbymassflowaretheinletoroutletports.控制體—控制面—系統(tǒng)入口—系統(tǒng)出口第12頁(yè)/共62頁(yè)Acontrolvolumemayinvolvefixed,moving,real,andimaginaryboundaries.第13頁(yè)/共62頁(yè)14TrueofFalse:Theboundaryisavirtualsurface.Theboundaryisanimaginarysurface.Theboundaryisanothersystem.Boundary（邊界，界面）Pleasenotethat:Thethicknessofasurfaceismathematicallyzero;Theboundarycanneithercontainmatternorfillavolumeinspace;Boundarymustbesharedbyboththesystemandtheenvironment,because,afterall,thesystemandtheenvironmentareincontactatthispoint.

第14頁(yè)/共62頁(yè)15Ifitisattemptingtoregardthewallastheboundarybetweenthesystem(TH)andtheenvironment(TL).BoundaryWall,notboundaryQQSystemEnvironmentTHTLSgenFluidAFluidBThedrawbackisthatunliketheheattransferinteractionQ,theentropytransferQ/Tisnotconservedasitpassesthroughtheboundary.Unfortunately,thefigurehelpsperpetuatethemysterythatsurroundsthedifferentconceptsofentropy,entropytransfer,andentropygeneration.第15頁(yè)/共62頁(yè)16Thetemperaturevariescontinuouslyacrosseachboundary,hence,boththeheattransferinteractionandentropytransferinteractionareconserved.Inthisfigure,thewallissituatedoutsidethesystem,andforthisreasontheentropygenerationduetothesystem-environmentheatinteractioncanbetermed“internal.”第16頁(yè)/共62頁(yè)17Thewallissituatedinsidethesystem,hence,theoppositechoiceismadeinthisfigure.Itisshownthatentropygenerationduetoenvironment-systemheatinteractioncanbetermed“external”relativetothesystem.第17頁(yè)/共62頁(yè)18Itisshownthatthesystemcanbedividedfurtherintosubsystem,ifthepreciseidentificationofthesourceofentropygeneration(wall)isoneoftheobjectiveofthethermodynamicanalysis.Theboundaryandthetypeofinteractionsthatpresentattheboundaryplayanimportantrole

inthestructure(organization)oftheanalysisdevotedtosolvingacertainproblem.第18頁(yè)/共62頁(yè)19thermodynamicpropertiesTheconceptofStatevariableisequaltothisofStateproperty,Twodescriptionsbelongtothethermodynamicproperties.StateVariable:todescribethestateofasystemintermsofmacroscopicparameterssuchasvolumeV,pressurep,temperatureT,molenumbersofthechemicalconstituentsNk,

whichareself-evident.

Functionsofstatevariables—statefunctions:Sincethefundamentalquantitiesinthermodynamicsarefunctionsofmanystatevariables,suchasenergyU,entropyS,enthalpyH,andsoon.

第19頁(yè)/共62頁(yè)20ExtensiveVariables:VariablessuchasvolumeVandmolenumberNk,whichareproportionaltothesizeofthesystem.IntensiveVariable:VariablessuchastemperatureTandpressurep,thatspecifyalocalproperty,whichareindependentofthesizeofsystem.ThermalEquilibrium:Heatwillflowuntiltheentiresystemreachesastateofuniformtemperature,thestateofthesystemiscalledthermalequilibrium.mVTpr1/2m1/2VTpr1/2m1/2VTpr第20頁(yè)/共62頁(yè)21Inthestateofthermalequilibrium,thevaluesoftotalinternalenergyUandentropySarecompletelyspecifiedbytemperatureT,thevolumeVandthemolenumbersofchemicalconstituentNk.U=U(T,V,Nk)S=S(T,V,Nk)AlsodescribedbyotherextensivestatesU=U(S,V,Nk)S=S(U,V,Nk)T=

(?U/?S)V,Nk第21頁(yè)/共62頁(yè)22Challengefromnon-equilibriumsystemsFornonequilibriumsysteminwhichthetemperatureisnotuniformbutiswelldefinedlocally.N(x),T(x)S(T,N),U(T,N),H(T,N)

UisnolongerafunctionsofotherextensivevariablessuchasS,V,andNdV第22頁(yè)/共62頁(yè)23TheCharacteristicofThermodynamicPropertiesThermodynamicproperties(StateVariables)areonlythosequantitieswhosenumericalvaluesdonotdependonthehistoryofthesystem(process),asthesystemevolvesbetweentwodifferentstates.Quantitiessuchaspressureandtemperaturearepropertiesbecausetheirvaluesdependstrictlyontheinstantaneousconditionduringwhichtheyaremeasured.whereasotherscanbederivedbasedonsuchmeasurements(e.g.,internalenergy,entropy,enthalpy,exergy).第23頁(yè)/共62頁(yè)24Itisnecessarytopayattentiontothequantities,whichareassociatedwiththehistoryofsystem.Thesequantitiesarenotthermodynamicproperties,suchaswork,heattransfer,masstransfer,entropytransfer,entropygeneration,lostavailablework,lostexergy,andsoon.However,wecanusethequantitiestodescribetheevolutionalprocessbetweenaninitialstateandafinalstate.第24頁(yè)/共62頁(yè)25PhaseAcertainphaseofasystemisthecollectionofallthepartsofthesystemthathavethesameintensivestateandthesameper-unit-massvaluesoftheextensiveproperties.第25頁(yè)/共62頁(yè)26Processorpathweusetheconceptofprocessasaone-wordreferencetothechangeofstatefromaninitialstatetoafinalstate.Toknowtheprocessmeanstoknownotonlytheendstatesbutalsotheinteractionsexperiencedbythesystemwhileincommunicationwithitsenvironment(e.g.,worktransfer,heattransfer,entropytransfer,masstransfer).第26頁(yè)/共62頁(yè)27thermodynamiccycleThethermodynamiccycleisaspecialprocessinwhichthefinalstatecoincideswithinitialstate.TheConceptofCycleEvolvedinto:AKeyConceptinthefieldofpowerengineeringAvehiclelogicaldeductioninthermodynamicstheory第27頁(yè)/共62頁(yè)28Stressingagainthefundamentaldifferencebetweenthermodynamicpropertiesandquantitiesthatarenot,notethatthechangesinquantitiesthatarenotpropertiesdependnotonlyontheendstatesbutalsoonthepath.第28頁(yè)/共62頁(yè)29Thermalequilibrium≠Thermodynamicequilibrium當(dāng)忽略重力引起壓力隨高度的變化當(dāng)在系統(tǒng)內(nèi)部沒(méi)有溫度梯度時(shí)當(dāng)系統(tǒng)內(nèi)部沒(méi)有擴(kuò)散或溶解及化學(xué)反應(yīng)時(shí)當(dāng)系統(tǒng)內(nèi)部不存在電位梯度時(shí)力平衡熱平衡化學(xué)平衡電平衡熱力學(xué)平衡狀態(tài)不存在各種不平衡勢(shì)第29頁(yè)/共62頁(yè)30TheFirstLawforClosedSystemsThefirstlawisnothingmorethantheprincipleoftheconservationofenergyappliedtophenomenainvolvingtheproductionofheatandabsorptionofheat.ClosedSystemHeatTransferWorkTransferEnergyChangeEnergyInteractions(Non-Properties)Property第30頁(yè)/共62頁(yè)31Aprocess–veryshortintervalInfinitesimalincrementsDifferentialnotation熱流，單位：J/s=W第31頁(yè)/共62頁(yè)32Heat（熱）熱是一種由溫差引起并流過(guò)系統(tǒng)邊界的能量形式。熱流

：表示能量流，它總伴隨著熵流其中：Q，熱量，單位：J

熱流，單位：J/s=WT，熱力學(xué)溫度，單位：K

，熵流，單位：W/K

第32頁(yè)/共62頁(yè)33Heat（熱）熱只是一種能量形式，而不是能量組成熱只與狀態(tài)改變的過(guò)程相關(guān)，而不用來(lái)描述物理狀態(tài)熱與功的差別：熱流總伴隨有熵流，而功表示系統(tǒng)邊界上無(wú)熵的能量傳遞形式系統(tǒng)內(nèi)的能量組成：熱力學(xué)能動(dòng)能勢(shì)能。。。系統(tǒng)邊界的能量傳遞熱功有熵?zé)o熵系統(tǒng)邊界第33頁(yè)/共62頁(yè)34第34頁(yè)/共62頁(yè)35第35頁(yè)/共62頁(yè)36第36頁(yè)/共62頁(yè)37第37頁(yè)/共62頁(yè)38第38頁(yè)/共62頁(yè)39第39頁(yè)/共62頁(yè)40第40頁(yè)/共62頁(yè)41熱力系能量結(jié)構(gòu)示意圖第41頁(yè)/共62頁(yè)42QuasistaticProcesses(準(zhǔn)靜態(tài)過(guò)程)如果不平衡位勢(shì)是無(wú)限小，因而系統(tǒng)在所有時(shí)間和狀態(tài)下都無(wú)限接近熱力學(xué)平衡狀態(tài)，這樣的過(guò)程則稱(chēng)為準(zhǔn)靜態(tài)過(guò)程，在p-v和T-s圖上可以表示出一條曲線。Reversibleprocesses(可逆過(guò)程)如果在過(guò)程終了時(shí)，系統(tǒng)和環(huán)境都可以恢復(fù)到初始狀態(tài)，在任何環(huán)節(jié)上都沒(méi)有留下任何變化，則說(shuō)系統(tǒng)經(jīng)歷了一個(gè)可逆過(guò)程。第42頁(yè)/共62頁(yè)43可逆過(guò)程與準(zhǔn)靜態(tài)過(guò)程區(qū)別可逆過(guò)程必然是準(zhǔn)靜態(tài)過(guò)程，一個(gè)可逆過(guò)程除了是準(zhǔn)靜態(tài)過(guò)程之外，還絕不能在過(guò)程中包括類(lèi)似固體或液體的摩擦、電阻、非彈性變形、磁滯、和極化滯后等引起系統(tǒng)產(chǎn)生熵增的任何效應(yīng)。第43頁(yè)/共62頁(yè)44HeatTransferAttention:TheFirstLawdoesnotdistinguishbetweenheattransferandworktransferastwopossibleformsofenergyinteractionbetweenasystemanditsenvironment.SupportingforthesecondlawHeattransferistheenergyinteractionaccompaniedbyentropytransfer,whereasworktransferistheenergyinteractionthattakesplaceintheabsenceofentropytransfer.

第44頁(yè)/共62頁(yè)45FurtherDefinitionEffectonthesystemandtheenvironmentfromHeattransfercannotbereproducedsuchthatthesoleeffectexternaltoeachsystemisthechangeinlevelofaweight.Theheattransferistheenergyinteractiondrivenbythetemperaturedifferencebetweenthesystemanditsenvironment.第45頁(yè)/共62頁(yè)46Adiabaticprocesses（絕熱過(guò)程）andDiathermalprocesses（透熱過(guò)程）AdiabaticprocessesThermalconductivityofthelocalmaterialissolowThetimeofheatinteractionissoshortRegardlessofthemagnitudeofthetemperaturegradientTemperaturegradientiszeroeveninthepresenceofheattransferNoRadiationDiathermalProcesses

Tomodelaboundaryasadiabaticordiathermalmeanstocomparethetimescaleoftheprocess,shorttime—adiabatic,longtime—diathermal第46頁(yè)/共62頁(yè)47EnergyChangeTotalEnergyChangeInternalEnergyKineticEnergyGravitationalPotentialEnergyOtherformsofenergystorage第47頁(yè)/共62頁(yè)48Eachenergystorageterm(E2-E1)icanbeincreasedordecreasedonlythroughacharacteristicenergyinteraction,beingindependentofoneanother.Twoformsofenergyinteraction

Theexistenceoftwoormoreenergyinteractionsthatcanaffectthesamemodeofenergystorage.Uncoupled

coupled

Forexample