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1、InternationalJournalofHeatandFluidFlow20(1999)142±148FlowcharacteristicsofwaterinmicrotubesGh.MohiuddinMala,DongqingLi*MechanicalEngineeringDepartment,UniversityofAlberta,Edmonton,CanadaT6G2G8Received25November1997;accepted12August1998AbstractWater¯owthroughmicrotubesw
2、ithdiametersrangingfrom50to254lmwasinvestigatedexperimentally.Microtubesoffusedsilica(FS)andstainlesssteel(SS)wereused.Pressuredropand¯owratesweremeasuredtoanalyzethe¯owcharacteristics.Theexperimentalresultsindicatesigni®cantdepartureof¯owcharacteristicsfromthepredicti
3、onsoftheconventionaltheoryformic-rotubeswithsmallerdiameters.Formicrotubeswithlargediameters,theexperimentalresultsareinroughagreementwiththeconventionaltheory.ForlowerRe,therequiredpressuredropisapproximatelythesameaspredictedbythePoiseuille¯owtheory.But,asReincreases
4、,thereisasigni®cantincreaseinpressuregradientcomparedtothatpredictedbythePoiseuille¯owtheory.Thefrictionfactorthereforeishigherthanthatgivenintheconventionaltheory.Theresultsalsoindicatematerialdependenceofthe¯owbehavior.Forthesame¯owrateandthesamediameter,anFSmicrotub
5、erequiresahigherpressuregradientthanastainlesssteelmicrotube.Themeasuredhighpressuregradientmaybeduetoeitheranearlytransitionfromlaminar¯owtoturbulent¯owortheeectsofsurfaceroughnessofthemicrotubes.Thesephenomenaarediscussedinthispaper.Aroughness-viscositymodelispropose
6、dtointerprettheexperimentaldata.Ó1999ElsevierScienceInc.Allrightsreserved.Keywords:Microchannel¯ow;Early¯owtransition;Surfaceroughness;Roughness-viscosityDPpressuregradientacrossthetube,N/m2Notationldynamicviscosityofwater,kg/msAcoecientsintheroughness-viscosityfunctio
7、nxrelaxationparameterCfrictionconstant,fRemkinematicviscosityofwater,m2/sCfrictionconstantratio,Eq.(10)qdensityofwater,kg/m3Ddiameterofthetube,mE1;E2;E3parametersinEqs.(15)and(16)SubscriptsFSfusedsilicaexpexperimentalvalueffrictionfactorththeoreticalvaluekheightofthe
8、roughnesselement,m1shorterlengthllengthofthetube,m22longerlengthPpressureatanypoint,N/mQvolume¯owrateofwaterthroughth
