Ontheoccurrenceofburnoutdownstreamofaflowobstacleinboilingtwo-phaseupwardflowwithinaverticalannularchannelOriginalResearchArticle

Ifaflowobstacle,suchasaspacerisplacedinaboilingtwo-phaseflowwithinachannel,thetemperatureonthesurfaceoftheheatingtubeisseverelyaffectedbytheexistenceofthespacer.Undercertainconditions,aspacerhasacoolingeffect,andunderotherconditions,thespacercausesdryoutofthecoolingwaterfilmontheheatingsurface.Theburnoutmechanism,whichalwaysoccursupstreamofaspacer,however,remainsunclear. Inapreviouspaper[Fukano,T.,Mori,S.,Akamatsu,S.,Baba,A.,2002.Relationbetweentemperaturefluctuationofaheatingsurfaceandgenerationofdrypatchcausedbyacylindricalspacerinaverticalboilingtwo-phaseupwardflowinanarrowannularchannel.Nucl.Eng.Des.217,81–90],wereportedthatthedisturbancewavehasasignificanteffectondryoutandburnoutoccurrenceandthataspacergreatlyaffectsthebehavioroftheliquidfilmdownstreamofthespacer. Inthepresentstudy,weexaminedindetailtheinfluencesofaspacerontheheattransferandfilmthicknesscharacteristicsdownstreamofthespacerbyconsideringtheresultinsteam–waterandair–watersystems.Themainresultsaresummarizedasfollows: (1) Thespaceraveragestheliquidfilminthedisturbancewaveflow.Asaresult,dryouttendsnottooccurdownstreamofthespacer.Thismeansthatlargetemperatureincreasesdonotoccurthere.However,tracesofdisturbancewavesremain,evenifthedisturbancewavesareaveragedbythespacer. (2) Thereisahighprobabilitythatthelocationatwhichburnoutoccursisupstreamofthedownstreamspacer,irrespectiveofthespacerspacing. (3) Thenewlyproposedburnoutoccurrencemodelcanexplainthephenomenathatburnoutdoesoccurupstreamofthedownstreamspacer,eveniftheliquidfilmthicknesstFmisapproximatelythesamebeforeandbehindthespacer.