NumericalanalysisofsupercriticalflowinstabilitiesinanaturalcirculationloopOriginalResearchArticle

NumericalstudieshavebeencarriedouttoinvestigateflowinstabilitiesinanaturalcirculationloopwithsupercriticalCO2.Forsteady-stateanddynamicanalysesoftheloopundersupercriticalconditions,asingle-channel,one-dimensionalmodelisdeveloped.Inthismodel,equationsfortheconservationofmass,momentumandenergyarediscretizedusinganimplicitfinitedifferencescheme.Acomputercodecalledflowinstabilityanalysisundersupercriticaloperatingconditions(FIASCO)iswritteninFORTRAN90tosimulatethedynamicsofnaturalcirculationloopswithsupercriticalfluid.Stabilityboundariesaredeterminedbysimulatingtheloopʹstimeevolutionfollowingasmallperturbationunderdifferentoperatingconditions.Stabilitythresholdresultssubstantiallydeviatefromtheresultsreportedbypreviousinvestigators,andcontradictsomeofthereportedfindings.Thedisagreementinresultsismostlikelyduetotheundesirabledissipativeanddispersiveeffectsproducedfromthelargetimestepsusedinpreviousstudies,therebyleadingtoalargerstableregionthanthosefoundusingsmallertimesteps.Resultspresentedinthispapersuggestthatthestabilitythresholdofanaturalcirculationloopwithsupercriticalfluidisnotconfinedtothenear-peakregionofthe(steadystate)flow-powercurve.Resultsobtainedfortherangeofparametervaluesusedinthisinvestigationalwayspredictthestabilitythresholdtobeinthepositivesloperegionofthe(steadystate)flow-powercurve.Parametricstudiesfordifferentoperatingconditionsrevealthesimilarityofstabilitycharacteristicsofflowundersupercriticalconditionswiththoseintwo-phaseflows.