ansys fluent教程fluent12-lecture07-heat-transfer

7-1ANSYS,Inc.Proprietary©2009ANSYS,Inc.Allrightsreserved.April28,2009Inventory#002600Chapter7HeatTransferModelingIntroductoryFLUENTTrainingHeatTransferModeling7-2ANSYS,Inc.Proprietary©2009ANSYS,Inc.Allrightsreserved.April28,2009Inventory#002600TrainingManualOutline•EnergyEquation•WallBoundaryConditions•ConjugateHeatTransfer•Thinandtwo-sidedwalls•NaturalConvection•RadiationModels•Reporting-ExportHeatTransferModeling7-3ANSYS,Inc.Proprietary©2009ANSYS,Inc.Allrightsreserved.April28,2009Inventory#002600TrainingManualEnergyEquation–Introduction•Energytransportequation:–EnergyEperunitmassisdefinedas:–Pressureworkandkineticenergyarealwaysaccountedforwithcompressibleflowsorwhenusingthedensity-basedsolvers.Forthepressure-basedsolver,theyareomittedandcanbeaddedthroughthetextcommand:–TheTUIcommanddefine/models/energy?Willgivemoreoptionswhenenablingtheenergyequation.ConductionSpeciesDiffusionViscousDissipationConductionUnsteadyEnthalpySource/SinkHeatTransferModeling7-4ANSYS,Inc.Proprietary©2009ANSYS,Inc.Allrightsreserved.April28,2009Inventory#002600TrainingManualEnergyEquationforSolidRegions•Abilitytocomputeconductionofheatthroughsolids•Energyequation:–histhesensibleenthalpy:•Anisotropicconductivityinsolids(pressure-basedsolveronly)HeatTransferModeling7-5ANSYS,Inc.Proprietary©2009ANSYS,Inc.Allrightsreserved.April28,2009Inventory#002600TrainingManualWallBoundaryConditions•Fivethermalconditions–HeatFlux–Temperature–Convection–simulatesanexternalconvectionenvironmentwhichisnotmodeled(user-prescribedheattransfercoefficient).–Radiation–simulatesanexternalradiationenvironmentwhichisnotmodeled(user-prescribedexternalemissivityandradiationtemperature).–Mixed–CombinationofConvectionandRadiationboundaryconditions.•Wallmaterialandthicknesscanbedefinedfor1Dorshellconductioncalculations.heattransfercalculations.HeatTransferModeling7-6ANSYS,Inc.Proprietary©2009ANSYS,Inc.Allrightsreserved.April28,2009Inventory#002600TrainingManualConjugateHeatTransfer•InCHT,heatconductioninsolidregionsiscoupledtoconvectiveheattransferinfluidregions.•MakesuseoftheCoupledboundaryconditiononwallzoneswhichdefinefluid/solidinterfaces.CoolantFlowPastHeatedRodsGridVelocityVectorsTemperatureContoursHeatTransferModeling7-7ANSYS,Inc.Proprietary©2009ANSYS,Inc.Allrightsreserved.April28,2009Inventory#002600TrainingManualConjugateHeatTransferExampleCircuitboard(externallycooled)k=0.1W/m∙Kh=1.5W/m2∙KT∞=298KAirinletV=0.5m/sT=298KElectronicComponent(onehalfismodeled)k=1.0W/m∙KHeatgenerationrateof2watts(eachcomponent)Topwall(externallycooled)h=1.5W/m2∙KT∞=298KSymmetryPlanesAiroutletHeatTransferModeling7-8ANSYS,Inc.Proprietary©2009ANSYS,Inc.Allrightsreserved.April28,2009Inventory#002600TrainingManualProblemSetup–HeatSource•Anenergy(heat)sourceisaddedtothesolidzonetosimulatetheheatgenerationbytheheat-generatingelectroniccomponents.HeatTransferModeling7-9ANSYS,Inc.Proprietary©2009ANSYS,Inc.Allrightsreserved.April28,2009Inventory#002600TrainingManualTemperatureDistribution(FrontandTopView)FlowdirectionConvectionBoundary1.5W/m2K298Kfreestreamtemp.Convectionboundary1.5W/m2K298KfreestreamtempFrontViewTopView(imagemirroredaboutsymmetryplane)Elect.Component(solidzone)2WattssourceBoard(solidzone)Air(fluidzone)298426410394378362346330314Temp.(ºF)FlowdirectionHeatTransferModeling7-10ANSYS,Inc.Proprietary©2009ANSYS,Inc.Allrightsreserved.April28,2009Inventory#002600TrainingManualAlternateModelingStrategies•Analternatetreatmentoftheboardsurfacewouldbetomodelitasawallwithspecifiedthickness(ThinWallmodel).•Inthiscase,thereisnoneedtomeshthelowersolidzone(representingtheboard).HeatTransferModeling7-11ANSYS,Inc.Proprietary©2009ANSYS,Inc.Allrightsreserved.April28,2009Inventory#002600TrainingManualMeshedWallvs.ThinWallApproach•Meshedwallapproach–Energyequationissolvedinasolidzonerepresentingthewall.–Wallthicknessmustbemeshed.–Thisisthemostaccurateapproachbutrequiresmoremeshingeffort.–Alwaysusesthecoupledthermalboundaryconditionsincetherearecellsonbothsidesofthewall.FluidzoneSolidzoneWallzone(withshadow)WallthermalresistancedirectlyaccountedforintheEnergyequation;Through-thicknesstemperaturedistributioniscalculated.Bidirectionalheatconductioniscalculated.HeatTransferModeling7-12ANSYS,Inc.Proprietary©2009ANSYS,Inc.Allrightsreserved.April28,2009Inventory#002600TrainingManualMeshedWallvs.ThinWallApproach•Thinwallapproach–Artificiallymodelsmodelsthethermalresistanceofthewall.–Necessarydataissuppliedthroughwallboundaryconditions(materialconductivityandthickness).–Usesthecoupledthermalboundaryconditiononlyforinternalwalls.FluidzoneWallzone(noshadow)Wallthermalresistanceiscalculatedusingartificialwallthicknessandmaterialtype.Through-thicknesstemperaturedistributionisassumedtobelinear.Conductionisonlycalculatedinthewall-normaldirectionunlessShellConductionisenabled.HeatTransferModeling7-13ANSYS,Inc.Proprietary©2009ANSYS,Inc.Allrightsreserved.April28,2009Inventory#002600TrainingManualShellConductionOption•Theshellconductionoptionisusedtoenablein-planeconductioncalculations.•Additionalconductioncellsa