Available online at www.51wendang.com

InternationalJournalofMultiphaseFlow34(2008)

1175–1184

www.51wendang.com ow

Multi-channele ectofcondensation owinamicro

triple-channelcondenser

WeiZhanga,b,JinliangXua,*,GuohuaLiua,b

a

MicroEnergySystemLaboratory,KeyLaboratoryofRenewableEnergyandGasHydrate,GuangzhouInstituteofEnergyConversion,

ChineseAcademyofSciences,Wushan,NengyuanRoad,Guangzhou,Guangdong510640,PRChina

b

GraduateUniversityofChineseAcademyofSciences,Beijing100039,PRChina

Received10April2008;receivedinrevisedform27May2008

Availableonline12June2008

Abstract

Multi-channele ectisimportanttounderstandtransportphenomenoninphasechangesystemswithparallelchannels.Inthispaper,visualizationstudieswereperformedtostudythemulti-channele ectinasilicontriple-channelcondenserwithanaspectratioof0.04.Saturatedwatervaporwaspumpedintothemicrocondenser,whichwashorizontallypositioned.Thecondenserwascooledbytheairnaturalconventionheattransferintheairenvironment.Flowpatternsareeithertheannular owathighinletvaporpressures,oraquasi-stableelongatedbubbleatthemicrochannelupstreamfollowedbyadetachingordetachedminiaturebubbleatsmallerinletvaporpressures.ThedownstreamminiaturebubblewasdetachedfromtheelongatedbubbletipinducedbythemaximumWebernumberthere.Itisobservedthateitherasinglevaporthreadordualvaporthreadsareatthefrontoftheelongatedbubble.Aminiaturebubbleisfullyformedbybreakingupthevaporthreadorthreads.Thetransientvaporthreadformationandbreakupprocessisexactlysymmetryagainstthecenterlineofthecenterchannel.Insidechannels,theMarangonie ectinducedbythesmalltemperaturevariationoverthechannelwidthdirectioncausesthevaporthreadformationandbreakupprocessdeviatingfromthesidechannelcenterlineandapproach-ingthecenterchannel.TheMarangonie ectfurtherforcesthedetachedbubbletorotateandapproachthecenterchannel,becausethecenterchannelalwayshashighertemperatures,indicatingthemulti-channele ect.Ó2008ElsevierLtd.Allrightsreserved.

Keywords:Condensation;Multi-channele ect;Flowpattern;Microchannel;Marangonie ect

1.Introduction

Condensationinmacrochannelshasbeenstudiedfornearlyonecenturyandiswellunderstood,involvingmanyengineeringapplications.Recently,miniaturizationofsys-temsbringsnewchallengesandopportunitiesonthecon-densation owandheattransfer.Principlesofcondensationinmacrochannelsmaynotbedirectlyappliedinmicrosystems,duetothepossiblesizee ect.Incontrasttothewidelystudiedmicroscaleboilingheattransfer,con-densationinmicrochannelsisnotwellunderstoodandneedsfurtherinvestigation.

*

Correspondingauthor.Tel./fax:+862087057656.E-mailaddress:xujl@ms.giec.ac.cn(J.Xu).

Bairdetal.(2003)developedanovelexperimentalapparatusallowingforaquantitativecontroloflocalheattransferto nepassagesthroughthermoelectriccooler.Localheattransfercoe cientswereobtainedforconden-sation owofHCFC-123andR11intubeswithinnerdiametersof0.92and1.95mm.Itisconcludedthatthetubediameterhadlittlee ectonthelocalheattransfer

´de´ricetal.(2005)visualizedthecondensa-coe cients.Me

tion owpatterninacapillarytubewiththeinnerdiam-eterof0.56mmandalengthof100mm.Testswereperformedusingn-pentaneastheworking uidatcon-stantmass uxesintherangeof0–18kg/m2s.Thetran-sientandtime-averagedvoidfractionsalongtheaxialpositionwereobtainedbyanalyzingthedigitalphoto-graphs.ShinandKim(2004)measuredlocalcondensationheattransfercoe cientsinsub-millimeterchannels.Using

0301-9322/$-seefrontmatterÓ2008ElsevierLtd.Allrightsreserved.doi:10.1016/j.ijmultiphase ow.2008.05.004