Anexperimentalstudyonthecriticalheatfluxforlowflowofwaterinanon-uniformlyheatedverticalrodbundleoverawiderangeofpressureconditionsOriginalResearchArticle

Anexperimentalstudyofthecriticalheatflux(CHF)hasbeenperformedforawaterflowinanon-uniformlyheatedvertical3×3rodbundleunderlowflowandawiderangeofpressureconditions.TheexperimentwasespeciallyfocusedontheparametrictrendsoftheCHFandtheapplicabilityoftheconventionalCHFcorrelationstoareturn-to-powerconditionsofamainsteamlinebreakaccidentwhoseconditionsmightbealowmassflux,intermediatepressure,andahighinletsubcooling.TheeffectsofthemassfluxandpressureontheCHFarerelativelylargeandcomplicatedinthelowpressureconditions.Atahighmassfluxoralowcriticalquality,thelocalheatfluxattheCHFlocationsharplydecreaseswithanincreasinglocalcriticalquality.However,atalowmassfluxorahighcriticalquality,thelocalheatfluxattheCHFlocationshowsanearlyconstantvalueregardlessoftheincreaseofthecriticalquality.TheCHFdataattheverylowmassfluxconditionsarecorrelatedwellbythechurn-to-annularflowtransitioncriterionortheflowreversalphenomena.SeveralconventionalCHFcorrelationspredictthepresentreturn-to-powerCHFdatawithreasonableaccuracies.However,thepredictioncapabilitiesbecomeworseinaverylowmassfluxofbelowabout100kg/(m2s).