Author/Authors :
ShojiMori، نويسنده , , AkiraTominaga، نويسنده , , TohruFukano، نويسنده ,
Abstract :
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.
