flow boiling in microchannels - texas a&m university：微通道中流动沸腾-德克萨斯&amp；m大学

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1、FlowBoilinginMicrochannelsAbhiishekVelichalaAnandVijaykumarEniolaEniketNellieRajarovaCourtesy-MKMoharan(IITK)INTRODUCTIONWhatisaMicrochannel?NeedtodissipatehighheatfluxesinMEMSandelectroniccoolingdevices.PioneeringworkonMicrochannels:Investigatedtheupperlimitofburnoutconditionsonsmalldiamete

2、rtubes[1964].TuckermanandPeasedemonstratedtheimportanceofmicrochannelsincoolingofintegratedcircuitry[1981].Classification:FlowBoilinginaMicrochannelFlowboilinginachannelisnothingbutboilingoccurringduetheflowofaliquidwithcertainvelocitywhosewallsaresubjectedtoheatMicrochannelflowsaredrivenbyp

3、umpswithmeanflowvelocitiesintherangeoffewmillimeterspersecondtomanycentimeterspersecondFlowinmicrochannelswillbemainlylaminarMicrochannelVsConventionalChannelThe2phaseheattransfercorrelationsformicrochannelsaredifferentfromconventionalchannelsSurfacetensionforcesaremoredominantandgravityforc

4、esarenegligibleinmicrochannelsSeparatestudiesneedtobeconductedformicrochannelsWhymicrochannel?FeaturesandmotivationHigherSurfaceDensityHigherHeatTransferCoefficients(h=Nu.k/D,Nu=constantforlaminarflow)LowThermalResistanceVolumetricheattransferratedependsinverselyonsquareofthechanneldiameterN

5、on-dimensionalgroupsSomeoftheimportantnon-dimensionalnumbersinflowboilingthroughmicrochannelaregivenbelow:Capillarynumber,Ca=μV/σWebernumber,We=DhG2/σρK1=(q/Ghfg)2*(ρl/ρg)K2=(q/hfg)2*(D/ρgσ)whydoweneeddimensionlessgroups?Theyareusefulatarrivingatkeybasicrelationshipsamongsystemvariablesthata

6、revalidfordifferentfluidsunderdifferentoperatingconditions.FLOWBOILINGREGIMESRef-Effectsofchanneldimension,heatflux,andmassfluxonflowboilingregimesinmicrochannels-TannazHarirchian,SureshV.GarimellaHeatTransferMechanismFlowboilingheattransferinmicrochannelisoftenassumedtobetheresultoftwodiffe

7、rentmechanisms,nucleateboilingandconvectiveboilingRapidEvaporation(NucleateBoiling)LiquidMotion(convectiveBoiling)Courtesy-Kandlikar…ContinuedThelocalheattransfercoefficient(h)iscalculatedasasumofthetwocontributionsi.e.,nucleateandconvectiveCorrela