HeattransportandvoidfractioningranulateddebrisOriginalResearchArticle

Thepaperdiscussestheboilingheattransferfromaporousbedwithinternalheatsourcesandreferstotheconfigurationinanuclearreactorafterapartialcoremelt.Theflowofcoolant,thetemperatureandthelocalliquid/vapordistributionwereinvestigatedinatwo-dimensionalconfiguration.Experimentswereconductedusingmonodispersebedsaswellasamixtureoftwodifferentparticlesizeswithatotalporositybelow20%.Insometeststhebedwassupportedbyashellofporousmaterialtocreateagapalongthebottomofthetestcontainer.Waterwasusedfortestsupto9%ofthecriticalpressure,whileothertestsweremadewithR134aupto44%ofthecriticalpressure.Themaximumheatingraterealizedinductivelywas730kW/m2.Theexperimentshavebeencomparedtoanalyticalresultswithaone-dimensionalapproach. Itisshownthatincontrarytothesituationinsmallcylindricalconfigurationstheheattransferwasincreasedbylargebuoyancydrivenconvectiveflows.Iftherewasagapalongthecontainerbottomanadditionalflowofliquidimprovedthecoolabilityofthebottomregioneveniftheupperpartoftheparticlebedwasalreadyoverheated.Incaseofhighdensityratios(wateratlowpressure),themeasurementsindicatedastrongenhancementofthecoolantflowaboveacertainminimumheatingrateresultingindecreasingvaporfractionvalueswhichwerenearlyindependentofthesystempressure.Thiswasassumedtobecausedbytheappearanceofverticalchannelsthroughwhichthevaporcouldflowthroughtheparticlebed.