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1、CompanyConfidentialCopyright2001FluentInc.Allrightsreserved.,1,NewInitiativesatFluentInc.,PhaseChangeinHeatExchangers,BrianBell,FluentInc.,UGM2001,CompanyConfidentialCopyright2001FluentInc.Allrightsreserved.,2,Motivation,DemonstratetheuseofFluenttomodelphasechangeinheatexchangersProcessesofinterestC
2、ondensationEvaporationBoilingIllustratehowtomodelonesuchprocessthroughuseofadetailedexampleShell-and-tubecondenserProvidemotivationforuserstobegindevelopingmodelsoftheirowndevices,CompanyConfidentialCopyright2001FluentInc.Allrightsreserved.,3,Outline,ProblemDescriptionShell-and-tubecondenserPurevapo
3、rcondensationNon-condensablegasesModelingApproachPorousmediumHeatandmasstransfermodelingModelImplementationUser-DefinedFunctionsandUser-DefinedMemoryResultsSteamcondenserwithnon-condensablegasesCommercialchillercondenser,CompanyConfidentialCopyright2001FluentInc.Allrightsreserved.,4,DescriptionofPro
4、blem,Shell-and-tubecondenser,CompanyConfidentialCopyright2001FluentInc.Allrightsreserved.,6,FilmCondensationProcess,DrivingpotentialforcondensationisthetemperaturedifferencebetweenvaporandcoolingwaterDrivingpotentialvariationcausedbyPressuredropRiseofcoolingwatertemperatureNon-condensables,CompanyCo
5、nfidentialCopyright2001FluentInc.Allrightsreserved.,7,CFDModelingTheory,PorousmediumapproachTubebundletreatedasporousmediumEnablescomputationallyefficientmodelingofentirecondenserComparisonwithdetailedmodelingapproachIn2-D,O(100)-O(1000)controlvolumespertubeversusmorethanonetubepercontrolvolumeHeata
6、ndmasstransfermodelsCondensationratecalculationCondensationratedeterminedfromlocalflowfieldandcoolingwatertemperatureLiquidfilmflowratetrackedinbundlefromtoptobottomCoolingwatertemperaturetrackedfrominlettooutlet,CompanyConfidentialCopyright2001FluentInc.Allrightsreserved.,8,PorousMediumApproach,Rep
7、resentationoftubebundleasporousmediumPorosityisonlyrequiredparameterPorositydefinedasratiooffluidvolumetototalvolume,Example:staggeredtubebundlewithequilateraltriangularlayout,Porosity,b,expressedas:,CompanyConfidentialCopyright2001FluentInc.Allrightsreserved.,9,TransportEquations,Generictransporteq
8、uationforporousmediumapproach,DistributedresistancetakesformofsourcetermsthatmodeldetailsoftheflowthatarenotresolvedbythegridPorosityinconvectionanddiffusiontermsnotmodeledinFluentDistributedresistancetermsmostsignificantintubebundleregion,CompanyConfidentialCopyright2001FluentInc.Allrightsreserved.
9、,10,EvaluationofModelingApproach,AdvantagesComputationallyefficientDoesanalternate,tractableapproachexist?ApproachdemonstratedtogivemeaningfuldatabyseveralauthorsDisadvantagesLossofsomeflowdetailsduetoaveragingCanbeovercomebydetailedmodelingofsmallregionsofcondenser,CompanyConfidentialCopyright2001F
10、luentInc.Allrightsreserved.,11,HeatTransferProcess,Filmcondensationonhorizontaltube,CoolingWater,TubeWall,CondensateFilm,Liquid-vaporInterface,RefrigerantVapor,Latentheatreleasedatliquid-vaporinterfacetransferredtocoolingwater,CompanyConfidentialCopyright2001FluentInc.Allrightsreserved.,12,HeatTrans
11、ferModel,HeattransferismodeledbycouplingofthermalresistancenetworkwithCFDcode,Tcw,Tt,i,Tt,o,Ti,Rcw,Rtube,Rcond,CoolingWater,CFDcodeprovidesinterfacetemperature,TiCoolingwaterandtubethermalresistancesaregenerallywell-knownFilmheattransfercoefficientisrequiredforRcond,CompanyConfidentialCopyright2001F
12、luentInc.Allrightsreserved.,13,FilmHeatTransferCoefficient,CriticalcomponentofheattransfermodelObtainfromexperiment,OrobtainfromliteratureSteamcondensationonsmoothtubes,FigurecourtesyofKansasStateUniversity,ProfessorSteveEckles,andDuaneL.Randall,CompanyConfidentialCopyright2001FluentInc.Allrightsres
13、erved.,14,ModelingAssumptions,EffectofliquidonflowfieldisneglectedApproachcanalsobeimplementedinEulerian-EulerianmultiphaseframeworkSatisfactorymodelforliquidphaserepresentationnotcurrentlyavailablePublishedresultsofthistypeofmodeldonotappeartoshowsignificantadvantageVaporisassumedtobesaturatedNosup
14、erheatingVaportemperaturedeterminedfrompressurefieldcalculatedbyCFDcode,CompanyConfidentialCopyright2001FluentInc.Allrightsreserved.,15,ImplementationofModelwithUDFs,UDFsarerequiredfor:SourcetermsrequiredbyporousmediumapproachCondensationratePressuredropinporousregionRepresentationoftubebundlePorosi
15、tyCondensatefilmflowrateaccountingCoolingwatertemperaturecalculationwithmultipletubepasses,CompanyConfidentialCopyright2001FluentInc.Allrightsreserved.,16,CoolingwatertemperaturecalculationforeachsegmentEveryiteration,condensationrateissummedovereachsegmentInletcoolingwatertemperature=outlettemperat
16、urefromprevioussegmentSegmentoutletcoolingwatertemperaturecalculatedbyenergybalance.Log-meantemperatureforeachsegmentcalculatedbasedonvaportemperatureandcoolingwaterinletandoutlettemperatures,TubeBundleRepresentation,BundleconsistsofNpassesandMsegmentsEachsegmentdefinedasuniquecellzone,Example:2PassbundleN=2,M=4,CompanyConfidentialCopyright2001FluentInc.Allrightsreserved.,17,TubeBundleGridStructure,Structured,cartesiangridusedintubebundleEachcontrolvolumehasuniquei,j,kindex,Gridstructu
