Analysis of steady state thermal hydraulic behaviour of the DEMO divertor cassette body cooling circuit F A d P a b c h • • • • • a A R R A A K D D C C T 1 w m f r p h p d h 0 ARTICLE IN PRESSG Model[.]
Trang 1Contents lists available atScienceDirect
j o u r n a l h o m e p a g e :w w w e l s e v i e r c o m / l o c a t e / f u s e n g d e s
P.A Di Maioa, S Garittaa, J.H Youb, G Mazzonec, E Vallonea,∗
a University of Palermo, Viale delle Scienze, Edificio 6, 90128 Palermo, Italy
b Max Planck Institute of Plasma Physics (E2 M), Boltzmann Str.2, 85748 Garching, Germany
c Department of Fusion and Technology for Nuclear Safety and Security, ENEA C.R Frascati, via E Fermi 45, 00044 Frascati, Roma, Italy
•Thermal-hydraulicstudyofDEMOdivertorcassettebodycoolingsystem
•Adoptionofacomputationalfluid-dynamicapproachbasedonfinitevolumemethod
•Comparativestudyonbothwaterandheliumcoolingoptions
•Assessmentofspatialdistributionsofpressuredrop,flowvelocityandtemperature
•Analysisofanimprovedlayout,leadingtosignificantperformancesenhancement
Article history:
Received 3 October 2016
Received in revised form 26 January 2017
Accepted 5 February 2017
Available online xxx
Keywords:
DEMO
Divertor
Cassette body
CFD analysis
Thermofluid-dynamics
WithintheframeworkoftheWorkPackageDIV1–“DivertorCassetteDesignandIntegration”ofthe EUROfusionaction,aresearchcampaignhasbeenjointlycarriedoutbyENEAandUniversityofPalermo
toinvestigatethethermal-hydraulicperformancesoftheDEMOdivertorcassettecoolingsystem.A com-parativeevaluationstudyhasbeenperformedconsideringthetwodifferentoptionsunderconsideration forthedivertorcassettebodycoolant,namelysubcooledpressurizedwaterandhelium
Theresearchactivityhasbeencarriedoutfollowingatheoretical-computationalapproachbasedon thefinitevolumemethodandadoptingaqualifiedComputationalFluid-Dynamic(CFD)code
CFDanalyseshavebeencarriedoutfortheconsideredoptionsofcassettebodycoolingcircuitunder nominalsteadystateconditionsandthepertainingthermal-hydraulicperformanceshavebeenassessed
intermsofoverallcoolantthermalrise,coolanttotalpressuredrop,flowvelocityandpumpingpower,to checkwhethertheycomplywiththecorrespondinglimits.Resultsobtainedarereportedandcritically discussed
©2017ElsevierB.V.Allrightsreserved
1 Introduction
TherecentEuropeanFusionDevelopmentAgreementroadmap
waselaboratedtopursuefusionasasustainable,secureand
com-mercial energy source[1] In this framework, thedivertor is a
fundamentalcomponentoffusionpowerplants,beingprimarily
responsibleforpowerexhaustandimpurityremovalviaguided
plasma exhaust.Due toitsposition and functions,thedivertor
hastosustainveryhighheatandparticlefluxesarisingfromthe
plasma(upto20MW/m2),whileexperiencinganintensenuclear
depositedpower,whichcouldjeopardizeitsstructure andlimit
∗ Corresponding author.
E-mail address: eugenio.vallone@unipa.it (E Vallone).
itslifetime Therefore, attentionhastobepaid tothe thermal-hydraulicdesignofitscoolingsystem,inordertoensureauniform andpropercooling,withoutanundulyhighpressuredrop WithintheframeworkoftheactivitiesforeseenbytheWP-DIV
1 “DivertorCassette Designand Integration”oftheEUROfusion action,aresearchcampaignhasbeencarriedoutattheUniversity
ofPalermo,in cooperationwithENEA,toinvestigatethesteady statethermal-hydraulicperformancesoftheDEMOdivertor cas-settebodycoolingcircuit,payinga specificattentiontothetwo differentoptionsunderconsiderationforitscoolant,namely sub-cooledpressurizedwaterandhelium
The research campaign has been carried out following a theoretical-numerical approach based on the Finite Volume Method and adopting the commercial Computational Fluid-Dynamic(CFD)codeANSYS CFXv.16.2,typicallyemployed also http://dx.doi.org/10.1016/j.fusengdes.2017.02.012
0920-3796/© 2017 Elsevier B.V All rights reserved.
Trang 2Fig 1. DEMO divertor cassette 2015 design.
Table 1
Summary of CB cooling options.
WCDC1 WCDC2 HCDC HCDC+B4C
toevaluateconcentratedhydraulicresistancestobeusedin
sys-temcodes[2,3].Theanalysismodelsandassumptionsareherein
reportedandcriticallydiscussed,togetherwiththemainresults
obtained
2 Cassette body cooling circuit
Accordingtoits2015design,DEMOdivertoriscomposedof54
toroidalcassettes,eacharticulatedinaCassetteBody(CB)that
sup-portstwotargetplateplasmafacingcomponents,namelyanInner
VerticalTarget(IVT)andanOuterVerticalTarget(OVT)(Fig.1)[4,5]
Fourdifferentcoolingoptionsarecurrentlyunderconsideration
fortheCBcoolingcircuit,thatdifferbothastocoolant,namely
pres-surizedwaterforWaterCooledDivertorCassette(WCDC)options
andheliumforHeliumCooledDivertorCassette(HCDC)options
[6],and totheiroperativeparameters Asummary of themain
CBcoolingoptionshasbeenreportedinTable1,togetherwitha
preliminaryassessmentoftheirthermal-hydraulicperformances,
carriedoutassumingnuclearheatingdatadrawnfrom[7]
Inlet BC T in = 350◦C T in = 150◦C
p s = 4.0 MPa p s = 3.5 MPa
Outlet BC G = 1.33 kg/s G = 5.71 kg/s
3 CB cooling circuit CFD analysis
Thethermal-hydraulicperformances ofboth theHCDC+B4C andWCDC1coolingoptionscurrentlyunderconsiderationforthe
CBcoolingcircuithavebeeninvestigatedundernominalconditions
byrunningseparate,steadystate,fully-coupledfluid-structureCFD analyseswiththeANSYSCFXv.16.2code
Inparticular,CFDanalyseshaveaimedtoassesstheCB thermal-hydraulicperformancesintermsof:
• coolantflowvelocitydistribution;
• coolantoverallpressuredrop;
• coolanttemperaturedistribution;
• CBstructuretemperaturedistribution
Moreover,foreachcoolingoptiontwoCBdesignconceptshave beenstudied,namelyDesignConceptI(DC-I),representingthe ini-tialCBreferencelayout,andDesignConceptII(DC-II),differingin flowpathsandinternalribthicknessfromthepreviousandset-up
toovercomethecriticalissuesrevealedbyCFDanalysis
Selectedmeshparametersandmainassumptions,modelsand boundaryconditions(BCs)adopted,maturedasafurther develop-mentof[8],aresummarizedinTables2and3.Adetailofthetypical meshset-upisshowninFig.2
3.1 DC-ICFDanalysisresults ThefluidandstructurecalculationdomainadoptedfortheDC-I CFDanalysisisreportedinFig.3
SteadystateCFDanalyseshavebeencarriedoutforboththe HCDC+B4CandWCDC1optionstoassesstheircooling effective-nessbycheckingwhethertheyallowthestructurethermalfield
tostaybelowthemaximumallowableEUROFERtemperatureof
550◦C[9]whileavoidingtheoccurrenceofcoolantsaturation,even locallyatthefluid-wallinterface
AstotheHCDC+B4Ccoolingoption,coolantflowvelocityand
CBstructuretemperaturedistributionsarereportedinFigs.4and5, showingsomeissuesmainlyconcerningthestructure
tempera-Table 2
Summary of the selected mesh parameters.
Trang 3Fig 2.Detail of a typical mesh set-up.
Fig 3. DC-I fluid and structure calculation domain.
Fig 4. DC-I: HCDC + B4C coolant flow velocity field.
Fig 5.DC-I: HCDC + B4C structure temperature field.
Fig 6. DC-I: WCDC1 coolant temperature field.
Fig 7. DC-I: WCDC1 structure temperature field.
Table 4
DC-I CFD analyses main results.
turefield.Infact,Fig.5showswidecriticalareaswherethewall temperatureovercomesthelimitof550◦C
AstotheWCDC1coolingoption,coolantandCBstructure tem-peraturedistributionsarereportedinFigs.6and7,indicatingthe occurrenceofCBcriticalareas
Inparticular,Fig.6showsthecoolantcriticalareas, conserva-tivelydefinedastheregionswherewatertemperatureovercomes the saturation temperature at the minimum pressure reached insidetheflowdomain.Fig.7showslocalizedcriticalareaswhere thewalltemperatureexceedsthelimitof550◦C.Finally,Table4 summarizesthemain resultsobtainedforboth coolingoptions CFDanalyses,additionallyshowingthattherearemorethanthree ordersofmagnitudebetweenheliumandwatercoolantcalculated pumpingpower
3.2 DC-IICFDanalysisresults
Inordertoimprovethethermal-hydraulicperformancesof
DC-I,andparticularlythoserelevanttothestructurethermalfield,the
CBDC-IIhasbeenpurposelydevised.Specifically,thepositionof inlet/outletmanifoldsattachmenthasbeenchanged(Fig.8)andthe thicknessofthestructureandofitsinternalribshasbeendecreased
Trang 4Fig 8.DC-I and DC-II manifolds attachment.
Fig 9.DC-I and DC-II structural differences.
Fig 10. DC-II: HCDC + B4C structure temperature field.
byafactor1.3÷2alongwiththatofthecornersunderIVTandOVT
(Fig.9).Thesechangeshaveaimedtoimproveflowuniformityand,
ingeneral,toenhancethecassettecoolingeffectiveness
Inanalogywiththepreviouscases,steadystateCFDanalyses
havebeencarriedoutfortheHCDC+B4CandtheWCDC1cooling
options
Resultsobtainedhaveshownthat,asitwasforecast,
temper-aturefieldsgloballyassessatlowervalues.EUROFERmaximum
temperature(550◦C)is overcomeinlargeareasofCB structure
onlyforHCDC+B4C(Fig.10).Furthermore,onlyextremely
local-izedcoolantvaporizationispredictedastoWCDC1(Fig.11).Finally,
Table5summarizesthemainresultsobtained,additionally
show-ingalimitedincreaseintheevaluatedpressuredropsandpumping
power
Fig 11.DC-II: WCDC1 coolant temperature field.
Table 5
DC-II CFD analyses main results.
4 Conclusions
WithintheframeworkoftheactivitiesforeseenintheWPDIVof theEUROfusionConsortium,acomputationalstudyhasbeen car-riedoutattheUniversityofPalermo,incooperationwithENEA,
toinvestigatethesteadystatethermal-hydrauliccooling perfor-mancesofthedivertorCBcoolingcircuit.Inordertoaccomplishthis task,twodifferentdesignconceptshavebeeninvestigated,namely DC-IandDC-II.Forbothcases,ahelium-cooled(HCDC+B4C)anda water-cooled(WCDC1)optionwasconsidered,respectively ThestudyhasrepresentedthefirststepoftheCBconceptual designandithasbeenuniquelyintendedtohavea preliminary assessmentofthethermal-hydraulicperformancesofthetwo cool-ingoptions underconsideration, startingfrom a “first-attempt” designof thecircuit, asacommonbasisfor boththetwo cool-ingoptions,tobefurtherrevisedaccordingtotheCFDanalysis indicationssotoimprovetheperformancesofeachcoolingoption Results obtainedfor theDC-I case indicated that thelayout needstoberevised, sinceitsbehaviourdoesnotfullymeetthe requirementsofsafetyandoperationtemperaturelimits.In par-ticular,structuralmaterialalwaysexceedsthemaximumallowed temperature(550◦C),nomatterwhattheadoptedcoolant was Moreover,watercoolantisexpectedtoexperiencevaporizations extensively.Theflowpathalsoneedstobeimprovedinorderto reachmoreeffectivecooling,particularlyattheoutboardCB cor-ners.AsforDC-IIoption,thestructureandtheflowpathswere revised.Asaconsequence,thetemperaturelevelofthestructural materialcouldbelargely reduced whilethemaximum allowed temperaturewasviolatedonly inthecase ofheliumcooling.In
Trang 5Finally,pressuredropspredictedforthisconceptareslightlyhigher
thanthoseofDC-I,regardlessofcoolant.Asfortherequired
pump-ingpowerfor all54Cassettes,it rangedbetween4.24MWand
4.97MWforheliumcoolingandbetween3and4kWinthecaseof
watercooling
Inconclusion,theCBthermal-hydraulicperformancescouldbe
significantlyenhancedbytheimprovedfeedingpipeconfiguration
(DesignConceptII)forboththetwocoolingoptionsinvestigated
Anyway,ithastobeunderlinedthat,atthisstageoftheactivity,
thedesignandworkingconditionsofthetwocoolingoptionsare
notmatureenoughtoallowanywell-posedcomparisonoftheir
performances.Tothispurpose,furthersolutionsarebeingstudied
astobothcircuitlay-outsandcoolantthermodynamicconditions,
purposelydevelopedforeachcoolingoption,toallowtheirfuture
well-posedcomparison
Acknowledgments
This work has been carried out within the framework of
theEUROfusionConsortium and hasreceivedfundingfromthe
Euratomresearchandtrainingprogramme2014–2018undergrant
agreementNo633053.Theviewsandopinionsexpressedhereindo
notnecessarilyreflectthoseoftheEuropeanCommission
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