Experimental investigation of post-dryout heat transfer in annuli with flow obstacles

(1)

ARTICLE IN PRESS

GModel

NED-6456; No.ofPages9

NuclearEngineeringandDesignxxx (2011) xxx–xxx

ContentslistsavailableatScienceDirect

Nuclear

Engineering

and

Design

jo u r n al h om ep a g e :w w w . e l s e v i e r . c o m / l o c a t e / n u c e n g d e s

Experimental

investigation

of

post-dryout

heat

transfer

in

annuli

with

ﬂow

obstacles

Ionut

Gheorghe

Anghel

∗

,

Henryk

Anglart,

Stellan

Hedberg

NuclearReactorTechnology,SchoolofEngineeringSciences,RoyalInstituteofTechnology(KTH),Roslagstullsbacken21,SE-10691Stockholm,Sweden

a

r

t

i

c

l

e

i

n

f

o

Articlehistory: Received7April2011

Receivedinrevisedform4August2011 Accepted5August2011

a

b

s

t

r

a

c

t

Anexperimentalstudyonpost-dryoutheattransferwasconductedintheHigh-pressureWAterTest (HWAT)loopattheRoyalInstituteofTechnologyinStockholm,Sweden.Theobjectiveoftheexperiments wastoinvestigatetheinfluenceofflowobstaclesonthepost-dryoutheattransfer.Theinvestigated operationalconditionsincludemassfluxequalto500kg/m2_s,_inlet_sub-cooling₁₀_K_and_system_pressure

5and7MPa.Theexperimentswereperformedinannuliinwhichthecentralrodwassupportedwith fivepinspacers.Twoadditionaltypesofflowobstacleswereplacedintheexitpartofthetestsection:a cylindersupportedonthecentralrodonlyandatypicalBWRgridspacercell.Themeasurementsindicate thatflowobstaclesimproveheattransferintheboilingchannel.Ithasbeenobservedthatthedryout powerishigherwhenadditionalobstaclesarepresent.Inadditionthewalltemperatureinpost-dryout heattransferregimeisreducedduetoincreasedturbulenceanddropdeposition.Thepresentdatacanbe usedforvalidationofcomputationalmodelsofpost-dryoutheattransferinchannelswithflowobstacles. © 2011 Elsevier B.V. All rights reserved.

1. Introduction

A forced convection heat transfer to a two-phase mixture consisting of the continuous vapour phase and the dispersed liquid phase, when the liquid film on the heater walls is no longersupported,istermedhereasthepost-dryout heat trans-ferregime.Othernamesusedintheliteraturetorefertothistype ofheattransferarepost-CHF(post-criticalheatflux),mistflowor dispersed-flowfilmboiling(DFFB).Oneofthecharacteristic fea-turesofpost-dryoutheattransferisadramaticreductionoftheheat transfercoefficient,andthusasignificantincreaseoftheheater walltemperature,ascomparedtotheconditionsbeforetheonset ofdryout.

Themaingoalofthepresentworkistoinvestigatethe influ-enceofflowobstaclesontheintensityofpost-dryoutheattransfer atconditionsrelevanttoBoilingWaterReactors(BWR) applica-tions.DuringthenormaloperationofBWRtheonsetofdryoutis precludedduetosufficientlyhighsafetymargins.However,during aBWRstart-up,whenthecoolantflowthroughthereactorcoreis relativelylowandthereactorpowerishighenough,corepower

∗ Correspondingauthor.Tel.:+46855378888.

E-mailaddresses:iganghel@kth.se(I.G.Anghel),henryk@kth.se(H.Anglart), stellan@energy.kth.se(S.Hedberg).

andflowinstabilitymayoccur.Duringsuchpowerandflow oscil-lationsshort-termpost-dryoutconditionsmightoccurinsomefuel rodassemblies.Forsafetyreasonsisthusimportanttopredictthe timehistoryofthecladwalltemperaturetoevaluateitsintegrity. Needlesstosaythatsuchpredictionsrequireknowledgeoftheheat transfercoefficientatgivenconditionsandtakingintoaccountthe geometrydetailsoffuelassemblies,inparticular,theinfluenceof spacergrids.

Post-dryoutheattransferhasbeeninvestigatedduringthepast severaldecadesandexperimentaldatahavebeenobtainedinboth simpletubesandinrodbundles(e.g.Koizumietal.,1987;Moon etal.,2005;Tuzlaetal.,1992).Theinfluenceofflowobstacleson post-dryoutheattransferatBWRconditionswasinvestigatedinan annulartestsectionwithasinglespacergridcellandasignificant improvement ofheat transfercoefficient wasreported(Anglart andPersson,2007).Thepresentexperimentsemployanannular testsectioninwhichtheinnerrodissupportedwithpinspacers, andtwoadditionalflow obstaclesareinsertedtomeasuretheir neteffectonthepost-dryout heattransfer.Thetest sectionhas beeninstrumentedwith88thermocouplestoallowfora signifi-cantimprovementoftheaccuracyofmeasurements,asdescribedin Angheletal.(2010).Duetothehighaccuracyofmeasurementsand thankstotheperformedanalysisoferrorpropagation,thepresent measurementsaresuitableforvalidationofcomputationalmodels ofpost-dryoutheattransfer.

(2)

ARTICLE IN PRESS

GModel

2 I.G.Angheletal./NuclearEngineeringandDesignxxx (2011) xxx–xxx

Fig.1.TheHigh-pressureWAterTest(HWAT)loop.

2. Experimentalfacility

2.1. Theloop

TheHigh-pressureWAterTest(HWAT)loopusedforthe post-dryout experimentswasdesigned tooperateatpressuresupto 25MPa.Allpartsincontactwithwater (exceptthetestsection) aremadeofstainlesssteel.Theloopconstructionallowsfortest sectionsupto7minlength.InFig.1asimpliﬁedﬂowdiagramof theloopispresented.

Themaincomponentsoftheloopare:feedwaterpump, cir-culationpump,ﬂowmeasurementsystem,automaticﬂowcontrol valve,pre-heater,testsection,condenserandblow-offvalve.A sec-ondarycircuitwithcoolantwaterat293.15Kisusedtocoolthe circulationpump.

Theloopisoperatingasfollows.Thecirculationwaterfirsthasto passthroughtheflowmeasurementsystem.Fromherewaterflows tothe155kWpre-heater,whichisneededtoadjusttheinlet tem-peraturetothetestsection.Lateron,subcooledwaterentersinto thetestsection.Afterthetestsection,thewater–steammixtureis passingthroughthecondenser.

Thewatercirculationintheloopisprovidedbythecirculation pump,which hasa pressureheadof100mwater, abigpartof thisbeingusedintheductsystembetweenthepumpandthetest sectiontosecureastableoperationoftheloop.

2.2. Testsection

The test section consists of 12.7mm×24.3mm×3650mm annulusassembledfromtwoconcentricpipes.Inthepresentwork theinnerpipeisreferredtoasarodwhiletheouterpipeisreferred toasa tube.Boththerodandthetubearemanufacturedfrom

Inconel600.Thismaterialhadbeenchosenbecauseofthesmallrate ofchangeoftheresistivitywiththetemperature(Inconel600).The designpressureandtemperatureforthetestsectionare18.3MPa and973K,respectively.

Twocopperrings,0.1mlongeach,weresolderedonboththerod andthetube.Inthepresentpaperthedistancebetweenthecopper ringsisreferredtoastheheatedlength.Theelectricalpowerwas suppliedviatwocopperelectrodesconnectedtothecopperrings.In ordertokeepheatlossesataninsignificantlevel,90mmthickglass fibreinsulationwasmountedaroundthetestsection.Nevertheless, forcalculationoftheheatfluxalltheheatlossesweretakeninto account.

Theexperimentswereconductedin threedifferenttest sec-tions:atestsectionwithpinspacersonlydenotedastestsection A,atestsectionwithpinspacersandcylindricalobstaclesdenoted astestsectionB,atestsectionwithpinspacersandgrid obsta-clesdenotedastestsectionC.Thefollowingoperationalconditions were employed in the experiments: inlet mass ﬂux equal to 500kg/m2_s,_inlet_sub-cooling_equal_to₁₀_K_and_system_pressure 5and7MPa.

Theblockageareaoftheﬂowobstaclesis:10.13%incaseofpin spacers,7.3%incaseofcylindricalobstaclesand10.07%incaseof gridobstacles.Theheatedlengthofallthreetestsectionstogether withpinspacersandﬂowobstaclesusedintheexperimentis pre-sentedinFig.2.

2.3. Temperaturemeasurements

Tocontroltheoperatingconditionsoftheloopoperationduring experiments,thetemperatureatsevenlocationsmustbemeasured onthecontinuousbasis.Thethermocouplesemployedfortheﬂuid

(3)

ARTICLE IN PRESS

GModel

I.G.Angheletal./NuclearEngineeringandDesignxxx (2011) xxx–xxx 3

Fig.2.Testsectionsemployedduringexperimentalruns.

measurementsweremountedinwells,120mmdeepand3mmin diameter.Themeasuredtemperaturesare:

• Coolantwatertemperaturefromsecondarycircuitofthe circula-tionpump;

• Coolantwatertemperatureoftheprimarycircuitbeforepump entrancetoavoidcavitations;

• Coolantwater temperature of theloop before theflow mea-surementsystemthatisnecessarytocalculateviscosity,specific volumeandthemassflux;

• Coolantwatertemperatureoftheloopafterpreheaternecessary toreﬁnetheinletconditionsbeforetestsection;

• Coolantwatertemperaturesatinletandoutletofthetestsection thatarenecessarytocalculateheatbalancebeforestartingtwo

phaseﬂow.Theinlettemperatureisneededtoconﬁrm experi-mentalconditions;

• Coolantwaterfromthesecondarycircuitofthecondenser. Thetemperatureoftheannuluswallswererecordedwith88 K-typethermocouples,40locatedaxiallyontheinsidesurfaceofthe rodand48locatedontheoutsidesurfaceofthetube.Thepresent workcontainstemperaturemeasurementsperformedontheinside surfaceoftherod.Thethermocouplesmountedinsideoftherod werearrangedinabundle.Onelayerofaglassﬁbretapeandone layerofamicatapewereusedtokeepthebundletightenedand toinsulateandprotectthethermocoupleheadsfromthe electri-callyconductinghotsurfaceoftheheatedwalls.Thethermocouples werepressedagainstthewallsurfacebysmallspringslocatedinthe

(4)

ARTICLE IN PRESS

GModel

Fig.3.Temperaturedeviationsforrod.

oppositelocationonthediagonal.Axiallocationsofthe thermocou-ples,whichareequaltoboth,thetubeandtherod,arepresented inTable1.Tocorrectthereadingsoftheassembledthermocouples atvarioustemperaturelevels,threeexperimentswereconducted foradiabatic,singlephasewaterﬂowwithinlettemperatureequal to298,383and483K.Thewalltemperaturedeviationsfromthe waterbulktemperaturearepresentedinFig.3.

2.4. Experimentalmethod

Eachseriesofexperimentswasinitiatedwithameasurement ofheatbalanceforsinglephaseflowinthetestsection.Inthatway theaccuracyofinstrumentationwaschecked.Atthebeginningof themeasurements,tochecktheaccuracyoftheinstrumentation, theheatbalancesforsinglephaseflowwereperformedeverytime. Thetemperaturesoftheliquidmeasuredattheinletandoutletof thetestsectionwereusedtodeterminetheenthalpygainoverthe heatedlength.Thecalculatedthermalpowerwascomparedwith theelectricalpoweroutputsuppliedtothetestsectionbytheDC generator,bymeanscurrentsandvoltages.Iftheerrorwerebelow 0.5%,inthecalculationsneededfortwo-phaseflow,theelectrical powerhasbeenused.

Thestandardmethodtoperformmeasurementsofpost-dryout heattransferincludesthefollowingsteps:

• forasetofchosenparameterssuchastheinletsubcooling,the massﬂuxandthepressure,thepoweroftheheaterissetslightly belowthelevelthatcorrespondstotheﬁrstoccurrenceofdryout inthetestsection,

• thepowerisincreasedstep-wise(keepingtherestofthe parame-tersconstant)andthetemperaturedistributionisrecordedonce thesteady-stateconditionisachieved.Theprocedureisrepeated forthesameinletconditions,employingallthreedifferentkinds ofﬂowobstacles.

Table1

Thethermocoupleslocationsontherodandtubewalls(distancefromthebeginning oftheheatedlengthinmillimetres).

T1 T2 T3 T4 T5 T6 T7 T8 T9 T10 1607 1657 2225 2275 2353 2452 2553 2601 2616 2627 T11 T12 T13 T14 T15 T16 T17 T18 T19 T20 2637 2712 2767 2822 2878 2933 2986 2997 3004 3009 T21 T22 T23 T24 T25 T26 T27 T28 T29 T30 3018 3070 3107 3145 3181 3219 3256 3293 3329 3367 T31 T32 T33 T34 T35 T36 T37 T38 T39 T40 3378 3383 3389 3398 3442 3475 3510 3544 3588 3611 2.5. Uncertainties

Intheexperimentalstudies,oneofthemostimportantissues istoevaluatethe accuracyof measurements.The uncertainties inthepresentstudycanbeclassiﬁedasfollows:uncertaintyofa measuredparameter,uncertaintyofaderivedvariableduetothe propagationofuncertaintiesofmeasuredvariablesanduncertainty duetonumericaliterations.Allmeasurementsof temperatures, pressure,pressuredrops,massﬂowrates,currentsand voltages aresubjectstoacertaindegreeofuncertainty:

• Uncertainty of temperature measurements is indi-cated for standard K thermocouples class 1 as: 1.5K (http://www.omega.co.uk/guides/Thermocouples.html). • Uncertainty of mass ﬂow rate measurements: ±0.5% (Flow

TechnologyInc.).

• Uncertaintyofstaticpressuremeasurements:±0.1%.

• Duringheatbalanceoperation,theelectricalpowerwas com-paredwiththeenthalpyincreaseoverthetestsectionandthe totalpoweruncertaintywasestimatedas±0.5%.

Theouterwalltemperatureoftherodandtheinnerwall tem-peratureofthetubearederivedfromtheconductionequationwith volumetricheatsources.Theoutersurfacetemperatureoftherod isobtainedas: Tro=Tri+ qv 2

r2 ri−r 2 ro 2 −r 2 ri ln rri rro

, (1)

whereTroisthewalltemperatureattheouter(wetted)surface,Tri

isthewalltemperatureattheinner(insulated)surface,riandrois theinner/outerradiusoftherodandqvistheheatsourceperunit

volume.

Theuncertaintyofthetemperatureoftherodoutersurfaceis foundas: uTro=

∂Tro ∂Tri uT_ri

2 +

∂Tro ∂qvuqv

2 +

∂Tro ∂ u

2

1/2 , (2)

whereuTriistheuncertaintyofthetemperatureoftheinnerrod

sur-face,uqvistheuncertaintyoftheheatsource,uistheuncertainty ofthethermalconductivityofthewallmaterialanduTrorepresents

thecalculateduncertaintyofthetemperatureoftherodouterwall surface.Numericalcalculationsindicatethatthisuncertaintyisless than1.53K,asshowninFig.4foratypicalexperimentalcase.

(5)

ARTICLE IN PRESS

GModel

Fig.4.Therodouterwalltemperaturewithindicatederror-bars.MassﬂuxG=500kg/m2_s,_inlet_subcooling_T₌₁₀_K,_pressure_P₌₅_MPa,_q₌₄₉₉_kW/m2_,_test_section_A.

3. Experimentalresults

3.1. Generaltrends

Thepresentstudyshowsthattheinfluenceofflowobstacleson post-dryoutheattransferisquitesignificant.Theirprimaryeffectis todisturbtheflowfieldofthevapourphasewhichinturncausesan increaseofthedepositionrateofliquiddroplets.Theeffecthowever dependsontheobstacleshapeanditsaxiallocation.Inthisstudy theneteffectofobstacleswasinvestigatedbycomparingthedata obtainedinthereferencetestsection(withpinsonly)andthetest sectionwithintroducedflow obstacles.Theresultsofrunswith threedifferentgeometries(testsectionsA,BandC)arepresented inFigs.5–12.Theheatfluxesincaseofrodandtubearedenotedas qrandqt.

Atypicaldevelopmentofthedryoutpatchcanbeobservedin Fig.5,showingexperimentalresultsobtainedintestsectionA. Ini-tialdrypatchappearsattheexitofthetestsectionwhenheatﬂux ontherodsurfaceisequalto509.7kW/m2_._After_increasing_the heatﬂuxto529.5kW/m2_,_the_rod_wetted_surface_superheat_at_the

testsectionexitincreasestoalmost300K.Inbothcases,thedryout patchisstilllocateddownstreamofthelastlevelofpinspacers. Whentheheatfluxisslightlyincreasedto529.9kW/m2_,_a_second dryoutpatchisdevelopedupstreamofthelastpinspacer posi-tion.Inthiscase,theeffectofthepinspacerisveryclear:thedry patchisquenchedjustdownstreamofthepinspacerandthe sur-facesuperheatisreducedtothevalueswhicharetypicalforthe pre-dryoutconditions.Inthelastexperimentalrun,theheatflux wasincreasedto534.3kW/m2_._As_a_consequence_wall_superheat increasedto250Kupstreamofthelastpinspacerlocation.Dueto theturbulenceinducedbythepinspacer,theliquidfilmwas re-madeandtheannularflowregimewasrestoredforapproximately 50mm.

3.2. Inﬂuenceofthecylindricalobstacle

Theneteffectofthecylindricalobstaclecanbeseenby compar-ingthemeasuredwallsuperheatshowninFigs.5and6.Asshown inFig.6,theﬁrstappearanceofadrypatchtakesplaceattheexit ofthetestsectionwhentheheatﬂuxattherodsurfaceisequal

(6)

ARTICLE IN PRESS

GModel

Fig.6.Measuredsuperheatofrodwallsurfaceforvariousheatﬂuxes.MassﬂuxG=500kg/m2_s,_inlet_subcooling_T₌₁₀_K,_pressure_P₌₅_MPa,_test_section_B.

Fig.7. Measuredsuperheatofrodwallsurfaceforvariousheatﬂuxes.MassﬂuxG=500kg/m2_s,_inlet_subcooling_T₌₁₀_K,_pressure_P₌₇_MPa,_test_section_A.

(7)

ARTICLE IN PRESS

GModel

Fig.9. Measuredsuperheatofrodwallsurfaceforvariousheatﬂuxes.MassﬂuxG=500kg/m2_s,_inlet_subcooling_T₌₁₀_K,_pressure_P₌_5–7_MPa,_test_section_B.

Fig.10.Measuredsuperheatofrodwallsurfaceforvariousheatﬂuxes.MassﬂuxG=500kg/m2_s,_inlet_subcooling_T₌₁₀_K,_pressure_P₌₇_MPa,_test_section_C.

(8)

ARTICLE IN PRESS

GModel

Fig.12.Measuredsuperheatofrodwallsurfaceforvariousheatﬂuxes.MassﬂuxG=500kg/m2_s,_inlet_subcooling_T₌₁₀_K,_pressure_P₌₇_MPa.

to519.5kW/m2,andthemeasuredmaximum wallsuperheatis equal to50K.IntestsectionA,which haspinspacersonly,the wallsuperheatisabout150Katslightlylowerheatfluxequalto 509.7kW/m2_._This_result_indicates_that_insertion_of_the_cylindrical flowobstaclebothincreasesthecriticalpowerlevelanddecreases thewallsuperheat,asexpected.Thiseffectcanbeexplainedby increaseofthedepositionrateofdropletscausedbythecylindrical flowobstacle.

When the heat flux on the rod surface is increased to 524.9kW/m2_,_a_second_dry_patch_appears_just_upstream_of_the_last pinspacer.Thisdrypatchslightlygrowsintheupstream direc-tionwhentherodsurfaceheatfluxisfurtherincreasedto543.2 and560kW/m2_._From_Fig.₅_it_can_be_seen_that_the_onset_of_dryout occursatapproximately3.1mfromthebeginningofheatedlength, whentheheatfluxontherodsurfaceisequalto534.3kW/m2_._The onsetofdryoutpointismovedabout80mmdownstreamwhenthe cylindricalobstacleisinsertedandtheheatfluxontherodsurface isincreasedto543.2kW/m2_.

Figs.7and8showtheeffectofthecylindricalobstacleatsystem pressureequalto7MPa,whereas.Itcanbeseen,thatinsertionof thecylindricalflowobstaclesincreasesthecriticalheatfluxfrom about463.1kW/m2_to_496.9_kW/m2_._It_is_interesting_to_note_that fortheheatfluxhigherthan537.7kW/m2_,_the_cylindrical obsta-cleiscausingatemperaturedropjustdownstreamofitslocation, however,fullquenchingofadrypatchisnottakingplace.Onthe contrary,afullquenchingofadrypatchiscausedbythelastpin spacer. Thisindicatesthat pinspacersaremoreeffectivein re-buildingtheliquidfilmthanthecylindricalobstacles.

Fig.9showstheeffectofpressureonheattransferandthe occur-renceofdryoutintestsectionwiththecylindricalobstacles.Ascan beseen,thepost-dryoutregimeprevailsatpressure7MPa,whereas nodryoutoccursatpressure5MPa,eventhoughtheheatﬂuxon therodsurfaceishigherinthelattercase.

3.3. Inﬂuenceofthegridobstacle

TheeffectofthegridobstaclecanbeseeninFig.10in compari-sonwithFig.7.Thefiguresshowthemeasuredwallsuperheatfor increasingpoweratsystempressureequalto7MPa.Theinsertion ofthegridflowobstaclesincreasesthecriticalheatfluxfromabout 463.1kW/m2_to_503.9_kW/m2_._This_result_indicates_that_grid_spacers areslightlymoreefficientinpreventingdryoutthanthe

cylindri-calobstacles.Aplausibleexplanationofthisdifferencemaybethe higherblockageratioofthegridobstaclecausinghigherturbulence levelandthushigherdepositionrateofdropletsdownstreamofthe obstacle.

Directcomparisonsoftheexperimentalresultsobtainedinall threetestsectionsareshowninFigs.11and12.Fig.11showsthe resultsobtainedinthethreetestsectionatalmostthesame opera-tionalconditions,withheatﬂuxontherodsurfaceinarangefrom 494.6to500.8kW/m2_._The_shown_results_correspond_to_fully devel-opedpost-dryoutconditionsintestsectionA,onsetofdryoutintest sectionBandpre-dryoutconditionsintestsectionC.Fig.12shows themeasuredrodsurfacesuperheatforthethreetestsectionat fullydevelopedpost-dryoutconditions.Itcanbeseenthatthe low-estwallsuperheatismeasuredintestsectionC,eventhoughthe appliedpoweristhehighest.

4. Summaryandconclusions

Newmeasurementsofpost-dryoutheattransferinannuliwith variousflowobstacleshavebeenpresented.Theexperimentshave beenperformedwithwater asworkingfluidatpressures5and 7MPa,inletmassflux 500kg/m2_s_and _inlet_sub-cooling₁₀_K._A thorough analysis of experimental uncertainties has been per-formedtoprovideaccuratedatathatcanbeusedfor validation ofcomputationalmodels.Ahighspatialresolutioninthe measure-mentshasbeenobtainedbyplacing88thermocouplesalongtest sections,fromwhich40thermocoupleshavebeenplacedinsideof theheatedrod.

Theneteffectsofthecylindricalandgridﬂowobstacleshave beenmeasuredbyusingareferencetestsectionwhereonlypin spacerswereusedtosupportthecentralrod.Itisconcludedthat ﬂowobstaclesimproveover-allcriticalpowerintestsections.This effectseemstodependontheobstaclelocation,shapeand block-ageratio.Inpost-dryoutregimetheobstacleseitherquenchthe drypatchdownstreamoftheirlocation,orreducethewall temper-ature.

Acknowledgment

TheﬁnancialsupportprovidedbySwedishCentreforNuclear Technology(SKC)isgratefullyacknowledged.

(9)

ARTICLE IN PRESS

GModel

References

Anghel,I.G.,Anglart,H.,Hedberg,S.,2010.Studyofpostdryoutheattransferin annu-luswithﬂowobstacles.In:Proc.14thInternationalHeattransferConference, IHTC-14,Washington,USA.

Anglart,H.,Persson,P.,2007.Experimentalinvestigationofpost-dryoutheattransfer withspacers.Int.J.MultiphaseFlows33(8),809–821.

FlowTechnologyInc.,CA03-UserManual.

Inconel600 detailedtechnicalreport.Availablefrom:<http://www.haraldpihl. se/engelsk/index.html>.

Koizumi,Y.,Kumamaru,H.,Yonomoto,T.,Tasaka,K.,1987.Post-dryoutheattransfer ofhigh-pressuresteam-watertwo-phaseﬂowinsinglerodchannelandmulti rodbundle.Nucl.Eng.Des.99,157–165.

Moon,S.-K.,Chun,S.-Y.,Cho,S.,2005.Anexperimentalstudyofpost-CHFheat transferforlowﬂowofwaterina3×3rodbundle.Nucl.Eng.Technol.37, 457–468.

Tuzla,K., Unal,C., Chen,J.C.,1992. An experimental study ofpost-CHF heat transfer in a 3× 3 rod bundle. In: Hewitt, G.F., Delhaye, J.M., Zuber, N. (Eds.),MultiphaseScienceandTechnology,Post-DryoutHeatTransfer.CRC Press.

Experimental investigation of post-dryout heat transfer in annuli with flow obstacles

ARTICLE IN PRESS

Nuclear

Engineering

and

Design

Experimental

investigation

of

post-dryout

heat

transfer

in

annuli

with

ﬂow

obstacles

Ionut

Gheorghe

Anghel

,

Henryk

Anglart,

Stellan

Hedberg

a

r

t

i

c

l

e

i

n

f

o

a

b

s

t

r

a

c

t

ARTICLE IN PRESS

ARTICLE IN PRESS

ARTICLE IN PRESS



ARTICLE IN PRESS

ARTICLE IN PRESS

ARTICLE IN PRESS

ARTICLE IN PRESS

ARTICLE IN PRESS