ExperimentalinvestigationonheattransfercharacteristicsinasafetyinjectionnozzlecomponentinPWROriginalResearchArticle

ThermalfatigueisapotentiallysignificantdegradationmechanisminNuclearPowerPlants(NPP).Forthefatigueanalysis,thethermalloadinformationaboutcomponentsmustbedeterminedfirstly.Inthispaper,anexperimentalstudywascarriedouttoobtainlocalfluidtemperaturesandlocalheattransfercoefficientsforthesafetyinjectionnozzlecomponentinreactorcoolantsystem(RCS).Inthismixingteecomponentahotjetissuesintoacoldcross-flowstreamfromanobliquepipeandtheturbulentmixingoftwofluidsinduceslocalcyclingstressesontheadjacentpipingwall.Experimentswereperformedusingaspecial-madeheatfluxmeter,whichcanmeasurethemixedfluidtemperatureclosetothewallandtheheattransfercoefficientbetweenthefluidandthewall.Plexiglassandmetallic1/9-scalemockupsweremanufacturedforflowvisualizationandheattransfertests,respectively.Alltestswereconductedatrangeof0–40forthejet-to-cross-flowvelocityratio.Theflowvisualizationtesthasobtainedgeneralpatternoftheflowandidentifiedsensitivezonesinthecomponentwherethejetandcross-flowinteractintensivelytocausethermalfatiguemorepossibly.Intheheattransfertest,heatfluxmeterswerepositionedinthewallatthesesensitivezones.Themeasurementresultsoftemperaturesandheattransfercoefficientshavebeendiscussedindetailinthepaper.TheseexperimentalresultsallowusimprovingthestateofknowledgeofthethermalloadtobeusedintheindustrialmixingteesinoperatingforlonglifetimeassessmentandforthedesigninthebasicNuclearPowerPlants.