AnexperimentalandanalyticalstudyoftheeffectofaxialpowerprofileonCHFOriginalResearchArticle

Theeffectofaxialheatfluxdistribution(AFD)onthecriticalheatflux(CHF)wasinvestigated.CHFmeasurementswereobtainedwithHFC-134acooledverticaltubeshavingfournon-uniformandoneuniformAFDprofiles.TheHFC-134atestconditionscoveredapressurerangefrom1.6to2.4MPa,amass-fluxrangefrom2.8to4.7Mgm−2s−1,andaninlet-qualityrangefrom−0.9to0.Thewater-equivalentpressureandmass-fluxrangesare10–14MPaand4–6.5Mgm−2s−1,respectively. Ingeneral,theobservedAFDeffectoncriticalpowerissmallathighinletsubcoolings.Atlowinletsubcoolings,thecriticalpowerfortheinlet-peakprofileisupto15%higherthanthatfortheoutlet-peakprofile.AlocalconditionsanalysisshowedthattheAFDhasthestrongesteffectonCHFathighdryoutqualities.CHFvaluesfornon-uniformAFDscouldbe50%lowerthanthosefortheuniformAFD.TheAFDeffectonCHFbecomesdiminishedwithdecreasingdryoutquality. FourdifferentapproachestoaccountfortheeffectofAFDonCHFwereassessedagainsttheexperimentalvaluesfromthecurrentexperiment.Theboiling-length-averageheat-fluxapproachwiththeboiling-lengthstartingpointattheonsetofannularflow(OAF)providedthebestpredictionofthecriticalpowerandtheCHFlocation.