Dropletentrainmentcorrelationinverticalupwardco-currentannulartwo-phaseflowOriginalResearchArticle

Upwardannulartwo-phaseflowinaverticaltubeischaracterizedbythepresenceofliquidfilmonthetubewallandentraineddropletladengasphaseflowingthroughthetubecore.Entrainmentfractioninannularflowisdefinedasafractionofthetotalliquidflowflowingintheformofdropletsthroughthecentralgascore.Itspredictionisimportantfortheestimationofpressuredropanddryoutinannularflow.Inthefollowingstudy,measurementsofentrainmentfractionhavebeenobtainedinverticalupwardco-currentair–waterannularflowcoveringwiderangesofpressureandflowconditions.Comparisonoftheexperimentaldatawiththeexistingentrainmentfractionpredictioncorrelationsrevealedtheirinadequaciesinsimulatingthetrendsobservedunderhighflowandhighpressureconditions.Furthermore,severalcorrelationsavailableintheliteratureareimplicitandrequireiterativecalculations. Analysisoftheexperimentaldatashowedthatthenon-dimensionalnumbers,Webernumber(We=ρg〈jg〉2D/σ(Δρ/ρg)1/4)andliquidphaseReynoldsnumber(Ref=ρf〈jf〉D/μf),successfullycollapsethedata.Inviewofthis,simple,explicitcorrelationwasdevelopedbasedonthesenon-dimensionalnumbersforthepredictionofentrainmentfraction.Thenewcorrelationsuccessfullypredictedthetrendsunderthehighflowandhighpressureconditionsobservedinthecurrentexperimentaldataandthedataavailableinopenliterature.However,inordertousetheproposedcorrelationitisnecessarytopredictthemaximumpossibleentrainmentfraction(orlimitingentrainmentfraction).Inthecurrentanalysis,anexperimentaldatabasedcorrelationwasusedforthispurpose.However,abettermodelorcorrelationisnecessaryforthemaximumpossibleentrainmentfraction.Atheoreticaldiscussiononthemechanismandmodelingofthemaximumpossibleentrainmentfractionconditionispresented.