models.heat.shell_and_tube_heat_exchanger.pdf

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1、SolvedwithCOMSOLMultiphysics4.3bShell-and-TubeHeatExchangerIntroductionShell-and-tubeheatexchangersarecommonlyusedinoilrefineriesandotherlarge-scalechemicalprocesses.Inthismodel,twoseparatedfluidsatdifferenttemperaturesflowthroughtheheatexchanger:onethroughthetubes(tubeside)andtheothert

2、hroughtheshellaroundthetubes(shellside).Severaldesignparametersandoperatingconditionsinfluencetheoptimalperformanceofashell-and-tubeheatexchanger.Themainpurposeofthismodelistoshowthebasicprinciplesforsettingupaheatexchangermodel.Itcanalsoserveasastartingpointformoresophisticatedapplicat

3、ions,suchasparameterstudiesoraddingadditionaleffectslikecorrosion,thermalstress,andvibration.ModelDefinitionFigure1showstheshell-and-tubeheatexchangergeometry.Inlet,airShellOutlet,waterTubesBafflesInlet,waterOutlet,airFigure1:Geometryoftheshell-and-tubeheatexchanger.©2013COMSOL1

4、SHELL-A

5、ND-TUBEHEATEXCHANGERSolvedwithCOMSOLMultiphysics4.3bTheheatexchangerismadeofstructuralsteel.Theparticipatingfluidsarewaterflowingthroughthetubesideandairflowingthroughtheshellside.Thebafflesintroducesomecross-flowtotheairandsuchincreasingtheareaofheatexchange.Anotheradvantageisthatbaffl

6、esreducevibrationduetothefluidmotion.ThismodelusestheNon-IsothermalFlowuserinterfacetogetherwiththek-εturbulencemodel.Ittakesadvantageofsymmetriestomodelonlyonehalfoftheheatexchanger,therebyreducingmodelsizeandcomputationalcosts.BOUNDARYCONDITIONSAllheatexchangerwallsincludingthebaffles

7、aremodeledasshellsin3D.Thisrequiresspecialboundaryconditionsfortheflowandheattransportequations.Theinteriorwallboundaryconditionfortheflowseparatesthefluidsfromeachotherandisalsousedtodescribethebaffles.Onbothsides,itappliesthewallfunctionsneededforsimulatingwallswiththek-εturbulencemod

8、el.Toaccountforthein-planeheatfluxintheshell,thehighlyconductivelayerboundaryconditionisapplied:–n⋅∇()–k∇T=–t⋅()–dsks∇tTHere,∇tisthetangentialderivative,dsisthelayerthickness,andksisthethermalconductivityoftheshell.Waterentersthetubesidewithavelocityof0.1m/sandatemperatureof80°