WP2.2: Boiling flow and Departure from Nucleate …

1 : Boiling flow andDeparture from Nucleate BoilingD. Bestion, C. Morel, S. Mimouni, E. Krepper, A. Badillo, Y. Sato, B. Niceno, M. C. Galassi, A. Del Nevo, F. Moretti, B. Koncar , M. Matkovi , L. Vyskocil, J. Macek, D. Tar , G. Mayer, G. Hazi, A. NURISP SEMINARA pril2-3, Karlsruhe1 Vyskocil, J. Macek, D. Tar , G. Mayer, G. Hazi, A. MarkusOBJECTIVES1. Better understandingof local flow processes in Boiling flow non-uniform heat flux grid effects, channel shape/size impact 2. Improvement of the subchannelapproach decrease of conservatismsthrough more general and accurate CHF correlationsNURISP SEMINARA pril2-3, Karlsruhe23. Help for design/optimizationof fuel assemblies parametric studies on design optimization of CHF test procedures, reduction of CHF of aCHF Local Predictive Approach DNB correlations based on local parametersinstead of cross-sectional averaged parameterstype 1type 2type 3type 4type 5type 6 MULTI-SCALE ANALYSIS OF DNBDNSLBM, VOF, LS PFNucleationBubble detachmentSeparate Effect TestsadiabaticAir water & steam-waterDEDALE, LiNX, TOPFLOW CHAPTALCFD modelsRod Bundle testsKFKI, BFBT, PSBT, LWLmodelingModelingvalidationvalidationv alidationModelingSubchannelcodesDNSLBM, VOF, LS PFNucleationBubble detachmentSeparate Effect TestsadiabaticAir water & steam-waterDEDALE, LiNX, TOPFLOW CHAPTALCFD modelsRod Bundle testsKFKI, BFBT, PSBT.

2 LWLmodelingModelingvalidationvalidationv alidationModelingSubchannelcodesNURISP SEMINARA pril2-3, Karlsruhe3 CFD models LES RANSS eparate Effect TestsBoiling flowASU, DEBORA, TESS ModelingFuel designModelingvalidationSubchannelcodesC HF predictionCFD models LES RANSS eparate Effect TestsBoiling flowASU, DEBORA, TESS ModelingFuel designModelingvalidationSubchannelcodesC HF predictionCFD MODELLING OF Boiling FLOWI dentification of important flow processes Exp. Data BASIS+ DNSMODEL OPTIONSNURISP SEMINARA pril2-3, Karlsruhe4 CLOSURE LAWS+ DNSMODEL OPTIONS Nb of fields Space and time resolutionSET OF EQUATIONSCFD MODEL OPTIONS FOR DNB RANS is OK ; no added value with LES 2-Fluid at least necessary to model all interfacial forces Turbulence modeled by k- , SST, or Rij- Efforts to predict bubble diameter: Monodispersed assumption: transport of n or Ai Polydispersion modeling by:NURISP Mid-term Review Meeting, October 7th, 2010 - BRUSSELS:Progress of SP2 activity at Mid-term5 Polydispersion modeling by: MUSIG approach MSM (statistical moments) Main efforts devoted to: Interfacial forces & H&M transfers Wall transfers : momentum, energy, DNB criterion 2-phase effects on turbulence polydispersionInterfacial forcesDragforce :Liftforce:Added Mass force :()lglgDliDlDgVVVVCa81 MMvvvvvv = = + + + = =lllggglMAMAlMAgVVtVVVtV121 CMMvvvvvvvvLTDNURISP SEMINARA pril2-3, Karlsruhe6 Liftforce.

3 Turbulent Dispersionforce : ()()lTllglLLlLgVVVVCMM vvvvvv = = = =llDTDTlDTgKCMMvv+ possibly a Wall lubrication forceCL may change sign when size increases (Tomiyama)DWBWall heat transfer & Interfacial heat transfersConvection :Vaporization :Quenching :()lwccTThAq =log+=TuChpll*log ()lwlqqqtaTTftAq =2 LNd6fqg3nuce =Models required for f, dnuc, & NNURISP SEMINARA pril2-3, Karlsruhe7 Quenching :qlqqqtaftAq =Liquid to Interface heat transfer()lsatililiTTahq =Nudhslli = +=NuTurbulence models Sato (1981): turbulence viscosity of the liquid phase + Increasing of the liquid viscosity by bubbles: Sources and sinks in turbulent ++= 2()()kturblSPkkvk+ + = + vNURISP SEMINARA pril2-3, Karlsruhe8()()klllllklllllllllSPkkvkt+ + = + vLGgdkklUUFSrrv = ()()() lllllllturblllllllllSCPCkvt+ + = + 21v kllSCS3= 2kCT=Bubble diameter in monodispersed approachBubble diameter in monodispersed approachBubble number density : Interfacial area density :()BKnCoalnCollnNucnnVndivtn +++=+ v63sdn =with :NURISP SEMINARA pril2-3, Karlsruhe9 Interfacial area density :663isad =with.

4 ()BKaCoalaCollnCollNucnnucgiggiiiiiidddt daVadivta ++++ =+ 22,32vBKniBKaCOniCoalaaaii 22336336 = =Data base for DNBvisualisationsBoiling flow Simple geometryLWLBFBT, PSBTB oiling flowreactor geometryCHF testsreactorgeometryNURISP SEMINARA pril2-3, Karlsruhe10 Adiabatic bubbly flowDedaleTopflowDeboraASUB oiling flow Simple geometryTurbulencepromoterAGATEKFKIR eview about DNB mechanisms and instability( Zuber, 1958) T reached( Unal, 1992; Bricard, 1995; Le Corre, 2007) spot spreading( Unal, 1992; Bricard, 1995; Ha & No, 2000; Le Corre, 2007) vaporization( Haramura, 1983; Celata, 1994; He, 2001) vaporization(Zhao, 2002), force instability(Beysens, 2003); rupture(Th ofanous, 2002)CEANURISP SEMINARA pril2-3, Karlsruhe11 Conclusion of the review No local DNB criterionfor CFD for convective Boiling No consensus on the DNB mechanismitself The very simple switch to film Boiling based on a limiting void fraction(NEPTUNE) performs not so badcompared to existing models but is not sufficiently precise Two different & complementary ways are proposed for future CEANURISP SEMINARA pril2-3, Karlsruhe12 Two different & complementary ways are proposed for future activities regarding the DNB prediction by CFD: Long term activity: identification of the DNB mechanism using new experimentsand the use of DNSsimulations Short term activity: establish a semi-empirical local DNB criterionwith some free parameters to fit on tube CHF data.

5 Then this DNB criterion could be confronted to a large data base including CHF in complex geometry. Direct Numerical Simulation of BoilingNumerical Method Navier-Stokes solver: PSI-BOIL- Finite Volume method on Cartesian grids- Projection method Interface tracking methodCIP-CSL2 (color function) with Phase change rate(kg/m3s):SVlqvqPSINURISP SEMINARA pril2-3, Karlsruhe13local interface sharpening scheme Phase change modelSharp Interface Model Features- Mass conservative scheme- Simple phase change modelPhase change rate(kg/m3s):lvqqSmLV+=&Latent heatCell volumeInterface areaHeat fluxesVerification: 3D Bubble Growth in Superheated Liquid Condition of simulation- Water and steam at 1 bar- Liquid superheat 5 C - Unbounded domain-Thermal boundary layer: about 10 m - Grid size: 8 m (Coarse), 4 m (Medium), 2 m (Fine) SEMINARA pril2-3, Karlsruhe14 Time (s)Radius(m).

6 Saturated Pool BoilingEXP.*Water at 1 (bar), Wall superheat = (K), Contact angle =47 PSINURISP SEMINARA pril2-3, (s) (s) (s) (s) (s) (s) (s) (s)PSI-BOIL*: R. Siegel, Keshock, Effects of reduced gravity on Nucleate Boiling bubble dynamics in saturated water, AIChE J., 10 (1964) 509-517. Calculation: Subcooled Pool BoilingHeat flux (W/m2) (s)Water at 1 (bar), Wall superheat = (K) , Contact angle =38 PSINURISP SEMINARA pril2-3, Karlsruhe16 Saturated boilingSubcooled Boiling (97 C) : key parameters of CHF are based on simple theoretical considerations ( force balance calculations) for the application of theories the problem has to be oversimplified numerical simulation can be used to approach real situationsObjective:to determine the functional relationship between thermophysical, geometrical parameters and the bubble detachment diameter, bubble release frequency taking into account more and more realistic situations --modelmodel --modelmodel --modelmodelUse of LBM for Boiling simulationsKFKINURISP SEMINARA pril2-3, Karlsruhe17 --modelmodelqqP, P, Tsat Tsatperiodicperiodicnono--slipslip --modelmodelqqP, P, Tsat Tsatperiodicperiodicnono--slipslip --modelmodelqqP, P, Tsat Tsatperiodicperiodicnono--slipslipheat conduction in the wallheat conduction in the wall + cavity in the wallqqP, P, Tsat Tsatperiodicperiodicnono--slipslipintera ction between cavities without cavity and without heat conduction in the wall, simple theories work fine()glbgD ~()4/121~ lglbgDf Dbvs.

7 G power function (exponents depends on the heating method, part of the heat escapes by natural convection) Dbvs. linear trend (slope lower with cavities) Dbvs. heat flux linear trend (slope influenced by cavity)Use of LBM for Boiling -model, homogeneous heating -model, inhomogeneous heating, q = 42900 W /m -model, inhomogeneous heating, q = 50050 W /mDeparture Diameter [mm]Contact Angle [ ] -model, inhomogeneous heating -model, inhomogeneous heating -model, inhomogeneous heating -model, homogeneous heating a = , b = a = , b = a = , b = a = , b = Diameter [mm]g, gravitation (x [m/s2])Dd=agbNURISP SEMINARA pril2-3, -model, homogeneous heating -model, inhomogeneous heating, q = 42900 W /m -model, inhomogeneous heating, q = 50050 W /mDeparture Diameter [mm]Contact Angle [ ] -model, inhomogeneous heating -model, inhomogeneous heating -model, inhomogeneous heating -model, homogeneous heating a = , b = a = , b = a = , b = a = , b = Diameter [mm]g, gravitation (x [m/s2])Dd= -model -model Dd = 910-6+ Diameter [mm]Heat Flux [W /m] , q = 42900 W /m-model, q = 50050 W /m-modelRelease Period [ms]Contact Angle [ ] f vs.

8 With flat surface the release period decreases sharply with increasing until it reaches minimum. With cavity the release period is a monotone increasing function of the and this function can be described well by a parabola. Use of LBM for Boiling simulationsKFKINURISP SEMINARA pril2-3, , q = 42900 W /m-model, q = 50050 W /m-modelRelease Period [ms]Contact Angle [ ] Increasing , Tw does not change at beginning then starts increasing (increase described by a cubic function of in line with data). where Tw starts to increase depends on modeling conduction or cavities. Modeling conduction, Tw starts increasing at higher for flat surface and even higher with cavities. Increasing , the Tw fluctuations increase, too. 5000 10000 15000 20000 25000 30000 35000 40000 45000300350400450500550-model-model-mode lSurface Temperature [ C]Heat Flux [W /m]Use of LBM for Boiling simulationsKFKINURISP SEMINARA pril2-3, Karlsruhe205000 10000 15000 20000 25000 30000 35000 40000 45000300350400450500550-model-model-mode lSurface Temperature [ C]Heat Flux [W /m] Cavities can interact with each other, resulting in cancellation or freezing of bubble production in a neighbouring cavity (energy partitioning between cavities)Is the wall Boiling model able to detect the CHF value?

9 Following the analysis of Kurul (1990), the heat flux at thewall is splitinto three terms: convective heat flux to liquid qcat the fraction of the wall area unaffected by the presence of bubbles, a quenching heat flux qqwhere bubbles Departure bring cold water in contact with the wall periodically,EDFNURISP Mid-term Review Meeting, October 7th, 2010 - BRUSSELS:Progress of SP2 activity at Mid-term21 a vaporisation heat flux qeneeded to generate the vapour heat fluxvaporisationquenchthe wall surface fraction A occupied by bubble nucleation reaches 1 in 8 CHF testsDEBORA cases under CHF conditions- Values of A under critical heat flux conditions are between10%and 70%. A was calculated as a function of the heat flux : A tends to 1 insome cases at CHF value but not in all cases.

10 Various authors (Zuber) postulate that CHF occurs when theHelmholtz instability appears in the interface of the largevaporcolumns leaving the heating surface bubble diameter ,theUnalEDFNURISP Mid-term Review Meeting, October 7th, 2010 - BRUSSELS:Progress of SP2 activity at ,theUnaldiameter and the Rayleigh-Taylor diameter tend towards thesame value when the heat flux tends towards the CHF value. Butthe accuracy levels should be improved to prove the efficiency ofthe criterion. The wall model for Nucleate Boiling is not able to detect the of Modeling: Bubble Dep. Diameter()6133coscos32sin864 + = gDvlbubble( )2n1iiiibubble(bubb)xxxDD = = [m]d(Dbubb)/d(fi)*U(fi)d(Dbubb)/d(sigma) *U(sigma)d(Dbub)