Analysisofexperimentsforin-tubesteamcondensationinthepresenceofnoncondensablegasesatalowpressureusingtheRELAP5/MOD3.2codemodifiedwithanon-iterativecondensationmodelOriginalResearchArticle

ThestandardRELAP5/MOD3.2codeismodifiedusingnon-iterativemodeling,whichisamechanisticmodeldevelopedforeasyengineeringapplicationtosimulatesteamcondensationinthepresenceofnoncondensablegasesinatube.Topredicttheliquid-sideheattransfercoefficientsinthemodifiedRELAP5/MOD3.2code,Nusselt’scorrelationisusedforthecondensationinaverticaltubeandKim’scorrelation,correlatedwiththeFroudenumberisusedforthecondensationinahorizontaltube.Inthemodifiedcode,thewallfrictioninaverticaltubeiscalculatedusingthetwo-phasefrictionfactorcorrelationproposedbyCollierandtheinterfacialfrictionfactoriscalculatedusingtheempiricalpower-lawrelationshipofChoi.BoththestandardandthemodifiedRELAP5/MOD3.2codesareusedtosimulatetwokindsofverticalin-tubeexperimentsandahorizontallystratifiedin-tubeexperimentinvolvingthecondensationphenomenoninthepresenceofnoncondensablegases.Twoverticalin-tubeexperiments,PassiveContainmentCoolingSystem(PCCS)condensationandrefluxcondensationexperiments,providedataonthesteady-statebehaviorswithatypicalflow,pressureandairmassfractionconditionslikelytobeseeninacondensingtubeofPCCSandinaU-tubeofasteamgeneratorinamid-loopoperation.Thehorizontallystratifiedin-tubeexperimentrepresentsthedirect-contactcondensationphenomenainahotlegofanuclearreactor.ThemodelingcapabilitiesofthemodifiedcodeaswellasthestandardcodeforsteamcondensationinthepresenceofnoncondensablegasesareassessedusingthesethreeKAISTcondensationexperiments.Themodifiedcodegivesabetterpredictionforthedataofthethreecondensationexperimentsthanthatofthestandardcode.SimulationresultsofPCCSandrefluxcondensationexperimentsshowthatthelocalheattransfercoefficientsarepredictedwellwiththemodifiedcodebutinthestandardversionofthecodetheyareunder-predictedbythedefaultmodelandover-predictedbythealternativemodel.Themodifiedcodepredictswelltheexperimentalvoidfractionusingthetwo-phasewallfrictionfactorcorrelation.Simulationresultsofthehorizontallystratifiedcondensationexperimentsshowthatthemodifiedcodepredictstheinterfacialheattransfercoefficientbetterthanthatofthestandardcode.