简介:Consideringthespecialresistancecharacteristicsoffluidsflowingthroughductswithsmallgaps,experimentsareperformedtoinvestigatetheresistancecharacteristicsofsingle-phasewater,whichisforcedtoflowthroughverticalannuli.Thegapsizesare0.9,1.4and2.4mm,respectively.Theexperimentsareconductedunderconditionof1atm.Thewaterintheannuliisheatedbyhightemperaturewaterreverselyflowingthroughtheinnertubeandtheouterannulus.TheresultsshowthattheflowpatternbegintochangefromlaminartoturbulentbeforeReynoldsnumberapproaches2000,theflowresistanceinannulushaslittlerelationswiththetemperaturedifferenceandwaysofbeingheated,butmainlydependsontheratioofmassfluxtothewidthofannulus.
简介:Boilingheattransferprocessisanalyzedinamoderatenarrowspaceconsistedoftwohorizontalplates,Themaindifferencebetweenthisprocessandtheconventionalunconfinedpoolboilingistheliquidsupplymechanismwhichisabsolutelypreventedbythegrowthofcoalescencebubblealongwiththeheatedsurfaceinthenarrowspace.Asaresult,themacrolayerbecomesthinnerduetotheevaporationoftheindividualbubbleswithinthemacrolayerduringtheperiodofbubblecoalescence,withorwithoutdryoutthatdependsonboththegapsizeofnarrowspaceandthesizeofheatedsurface.Foraspecifiedsizeoftheheatedsurface,theinitialthicknessoftheliquidlayerhasacriticalvaluewhichapproachesaconstantwhilethespaceheightislargerthanacriticalvalue.Theindividualbubblebehaviorsandtheheattransfercanbeconsideredasthesameasthatintheunconfinedpoolboiling,ifthespacegapislarge,However,theindividualbubblesdonotgenerateinthelastperiodofthebubblecoalescenceandalowermaximumheatfluxwillberesultedifthespacegapisreduced.Insuchacase,themacrolayerisdryout.
简介:ZnOnanoparticleswithverynarrowsizedistributionweresynthesizedbycouplinghomogeneousprecipitationwithmicroemulsionunderpulsedmicrowaveheating.TheconditionsofpreparingZnOnanoparticleswereinvestigated.TheproductswerecharacterizedwithDTA,TGA,XRD,TEMandUV-Vis.ThesynthesizedZnOnanoparticeshadmuchstrongerultravioletabsorptivitythannormalZnOpowders;theaveragesizeofproductswassensitivetothevariationofthepowerordurationofmicrowaveirradiation.
简介:本文介绍了按常规光器件制作工艺可实现的几种新型可调谐窄带光滤波器的原理及性能,简单分析了各自的功能特点与不足。