Development and Validation of the Wall Boiling Model in ANSYS CFD

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Burns PBU, Funded CFD Development ANSYS Germany Thomas.Frank@ansys.

1 Development and Validation of the Wall Boiling Model in ANSYS CFD Th. Frank, C. Lifante, A.D. Burns PBU, Funded CFD Development ANSYS Germany E. Krepper, R. Rzehak FZ Dresden-Rossendorf (FZD) 2009 ANSYS, Inc. All rights reserved. 1 ANSYS, Inc. Proprietary

Boiling & CHT FRIGG loop: Boiling in heated rod bundles Summary &

2 Outline Motivation The wall boiling model in ANSYS CFD Boiling model validation Wall boiling in vertical pipes Boiling & recondensation Boiling & CHT FRIGG loop: Boiling in heated rod bundles Summary & Outlook 2009 ANSYS, Inc. All rights reserved. 2 ANSYS, Inc. Proprietary

Introduction Towards CFD for Flows through Nuclear Fuel Assemblies Prediction of boiling flow through fuel assemblies Optimization of fuel assembly and spacer

steam seperator To conenser High pressure coolers 5MW Circulation pump 10 MW Void Fraction Measurement Device Feed water P el.

3 Introduction Towards CFD for Flows through Nuclear Fuel Assemblies Prediction of boiling flow through fuel assemblies Optimization of fuel assembly and spacer grid design Replacement/supplementation of very expensive experiments by knowledge obtained from CFD simulations Direct contact condenser Pressurizer Water steam seperator To conenser High pressure coolers 5MW Circulation pump 10 MW Void Fraction Measurement Device Feed water P el. 9,5MW PWR Test Vessel p 185 bar P 15 MW el. Control valve BWR Test Vessel p 110 bar Control valve Downcomer Natural Circulation Loop 2009 ANSYS, Inc. All rights reserved. 3 ANSYS, Inc. Proprietary

Multiphase Flow Modeling FSI: Stresses & Deformations Validation against

4 CFD Simulation for Fuel Assemblies in Nuclear Reactors Material Properties Wall Boiling & Bulk Condensation Turbulence Conjugate Heat Transfer (CHT) Multiphase Flow Modeling FSI: Stresses & Deformations Validation against Experiments 2009 ANSYS, Inc. All rights reserved. 4 ANSYS, Inc. Proprietary

5 Multiphase Flow Regimes for Boiling Water Flow subcooled flow bubbly flow slug flow annular flow spray flow T ONB OSB wall temperature T sat mean fluid temperature subcooled boiling nucleate boiling (saturated boiling) x 2009 ANSYS, Inc. All rights reserved. 5 ANSYS, Inc. Proprietary

6 Flows with Subcooled Boiling (DNB) RPI-Wall Boiling Model Mechanistic wall heat partioning model: q & = q& + q& + Wall F Q q& E convective heat flux quenching heat flux evaporation heat flux q& q& = A h ( T T ) q& = m & (h h ) F = A1 hf ( TW TL ) Q 2 Q W L E G L y A 2 A1 A 2 Convective heat flux u Quenching heat flux m& * m& * m& * t 2009 ANSYS, Inc. All rights reserved. 6 ANSYS, Inc. Proprietary

7 Grid Dependent Correlations Quenching heat flux 1-D q& Q = A2 hq ( TW TL ) h = 2 f Q t W ρlc π PL λ L y T L 1-D approach T L first grid node with refining grid CFD T L T Sat T W 2009 ANSYS, Inc. All rights reserved. 7 ANSYS, Inc. Proprietary

8 Grid Dependent Correlations Evaporation heat flux q& = m & (h h ) E G L m& = d W π d 6 3 W ρ G f n T = min 1.4 mm, 0.6 mm exp d W bubble departure diameter n nucleation site density per m² f bubble departure frequency S [ K] TL [ K] 45[ K] small quenching & overestimated evaporation on fine grids wrong heat flux partitioning tends to film boiling on fine grids (due to T L T W ) 2009 ANSYS, Inc. All rights reserved. 8 ANSYS, Inc. Proprietary

9 Revisited RPI Boiling Model Grid invariance of the model required determine T L from temperature wall function (Kader, 1981) T = Pr y e ln( y ) + β e + + ( Γ ) + ( 1/ Γ) + ρl y u y = µ from definition of T + : + ρ c u PL τ T = (TW T L ) q& W τ evaluating T + at 2 different locations/wall distances y ANSYS, Inc. All rights reserved. 9 ANSYS, Inc. Proprietary

10 Revisited RPI Boiling Model heat flux in boundary layer identical at both locations ρ c u q & = (T T ) PL τ W, y + = first cell + W L y first cell T + = + y = first cell ρ c u q & = (T T ) PL τ + W L + W, y = const + y = const T y + = const heat fluxes are equal + T + y = const TW TL = TW T + T y + = const y + + = first cell y = first cell L additional factor in correlations for d q& q& W, F, Q assumption of y + const=250; model parameter Replace (T W -T L ) in submodel expressions with the above relation 2009 ANSYS, Inc. All rights reserved. 10 ANSYS, Inc. Proprietary

11 RPI-Wall Boiling Model Submodels for Model Closure Submodels for closure of RPI wall boiling model: Nucleation site density: Lemmert & Chawla, User Defined Bubble departure diameter: Tolubinski & Kostanchuk, Unal, Fritz, User Defined Bubble detachment frequency: Terminal rise velocity over Departure Diameter, User Defined Bubble waiting time: Proportional to Detachment Period, User Defined Quenching heat transfer: Del Valle & Kenning, User Defined Turbulent Wall Function for liquid convective heat transfer coefficient Correlation for bulk flow mean bubble diameter required: e.g. Kurul & Podowski correlation via CCL Supported combination of wall boiling & CHT in the solid GGI & 1:1 solid-fluid interfaces 2009 ANSYS, Inc. All rights reserved. 11 ANSYS, Inc. Proprietary

13 ANSYS Fluent 13.0 Wall Boiling Modeling Wall boiling Based on same RPI nucleate boiling & heat flux partitioning model Non-equilibrium subcooled boiling Will support superheated vapor (convective heat flux to vapor) Contours of vapor volume fraction in a heated rod bundle 2009 ANSYS, Inc. All rights reserved. 13 ANSYS, Inc. Proprietary

14 ANSYS CFX R&D Development Work in Progress Ongoing R&D and development: Provide more user interfaces to the RPI boiling model User defined area fractions A 1 and A 2 User defined terms for convective, quenching and evaporative heat fluxes Q F, Q Q, Q E User defined 4th component of wall heat partitioning, e.g. heat flux to vapor CFX5Pre GUI extension Extended output to CFD-Post All extensions are part of a collaborative R&D project with FZD customized CFX solver 2009 ANSYS, Inc. All rights reserved. 14 ANSYS, Inc. Proprietary

15 New Capabilities: CCL Access to Area Fractions WALL BOILING MODEL PARTITIONING AREA FRACTIONS Option = Standard / User Defined Under User Defined convective, quenching and evaporative area can be introduced 2009 ANSYS, Inc. All rights reserved. 15 ANSYS, Inc. Proprietary

flux partitioning algorithm with a 4th component of the wall heat

19 CCL & User Routine for 4th Wall Heat Partitioning Component Customization of CFX5Pre for the extension of the RPI wall heat flux partitioning algorithm with a 4th component of the wall heat flux splitting 2009 ANSYS, Inc. All rights reserved. 19 ANSYS, Inc. Proprietary

22 The Bartolomej Test Case R = 7.7 mm Variable Value Z= 2 m q=0.57mw W/m 2 P 4.5MPa R 7.7 mm G in 900 kg/(s m2) q& 0.57MW/m2 Subcooling 58.2 K G in =900 kg/(s m 2 ) 2009 ANSYS, Inc. All rights reserved. 22 ANSYS, Inc. Proprietary

23 Multiphase Flow Model Steam-Water 2-phase flow: Water: continuous phase Water Steam: disperse bubbles (particle model) Material properties (EOS): IAPWS-IF97 water - water steam property tables Modified law for interfacial area Kurul & Podowski type bulk bubble diameter: d B =f(t sub ) Accounting for higher volume fraction of the steam phase Turbulence Model SST turbulence model for continuous phase 0-eq. disperse phase turb. model + Sato bubble induced turbulence 2009 ANSYS, Inc. All rights reserved. 23 ANSYS, Inc. Proprietary

24 Inter-Phase Mass, Momentum and Energy Transfer Mass transfer model Thermal Phase Change Model (bulk boiling/condensation model) RPI wall boiling model Momentum transfer models Grace drag FAD turbulent dispersion force Tomiyama lift force Wall lubrication force (none, Antal, Frank, Tomiyama) Heat transfer models Water: Thermal Energy Water Steam: Saturation temperature Two resistance model Ranz Marshall correlation for bubble heat transfer 2009 ANSYS, Inc. All rights reserved. 24 ANSYS, Inc. Proprietary

25 Numerical Grids Validation on mesh hierarchy with regular refinement factor of 4 (2d meshes) Grid Grid1 Grid2 Grid3 # Nodes (uniform) 20x150 40x300 80x600 Max y t [s] x ANSYS, Inc. All rights reserved. 25 ANSYS, Inc. Proprietary

30 Comparison to Experimental Data - Parameter & Model Variation Influence of wall heat flux: Influence of wall lubrication force model: 2009 ANSYS, Inc. All rights reserved. 30 ANSYS, Inc. Proprietary

32 Geometry & Flow Parameters Geometry Pipe flow; axial symmetry Inner radius of pipe R = mm Total pipe length L T = 1.4 m Heated section length L H = 1.0 m Flow parameters Upward directed water flow p in = 6.89 Mpa Parameter Investigation L T L H R Outlet Adiabatic Wall Symmetry Axis q wall Heated Wall Mass G in Liquid T in Wall heat flux q wall G in,t in, p in Inlet 2009 ANSYS, Inc. All rights reserved. 32 ANSYS, Inc. Proprietary

33 Testcase Parameters Measurement data of zonal-averaged cross-sectional steam volume fraction distribution over pipe length are available for 3 different parameter setups: Experiment No. q Wall [MW m^-2] G in [kg m^-2 s^-1] T in [K] ANSYS, Inc. All rights reserved. 33 ANSYS, Inc. Proprietary

$3 (Mesh01) Distribution of water temperature and steam volume fraction$

$3 (Mesh02) Distribution of water temperature and steam volume fraction$

$temperature and steam volume fraction$

$3 (Mesh04) Distribution of water temperature and steam volume fraction$

39 Interface Heat Transfer Models Investigation of the influence of different interface heat transfer models for liquid phase Ranz-Marshall (Baseline Setup) Nu = Re 0.5 Pr 0.3 Hughmark Nu = Re Nu = Re Tomiyama 0.5 Pr Pr 0.3 Nu = Re 0.8 Pr Re Re 2009 ANSYS, Inc. All rights reserved. 39 ANSYS, Inc. Proprietary

42 Lee et al. (2008) Experiment Axially symmetric circular annulus Radial dimensions Inner radius of outer tube: R = mm Outer radius of inner tube: R 0 = 9.5 mm r Outlet R R0 R C Measuring Plane (for experimental and numerical Results) Core radius: R C = 3/4 R 0 Annulus width: 9.25 mm Axial dimensions Total heating section height: L T = 1670 mm Distance between inlet and measuring plane: L M = 1610 mm L M L T Heated Wall Adiabatic Wall Radial Position: R P Dimensionless, radial distance from inner tube (R P = 0) to outer tube (R P = 1) across the annulus: R P = ( r R0 ) ( R R ) ANSYS, Inc. All rights reserved. 42 ANSYS, Inc. Proprietary Axis Inlet Inner Tube (Heating Rod) Annulus Outer Tube z

43 Investigated Geometry Configurations HFO (Heat Flux Only): Fluid Domain (Annulus) area specific heat flux boundary condition # Outlet Fluid Domain Inlet CHT (Conjugated Heat Transfer): Fluid Domain (Annulus) + Solid Domain (Heated Rod Core) + Solid Domain (Non-Heated Rod Cladding) volume specific heat source # Outlet Solid Domain # Solid Domain Fluid Domain Inlet 2009 ANSYS, Inc. All rights reserved. 43 ANSYS, Inc. Proprietary

44 Selected Testcase Conditions Selected two (out of 12) datasets: Set 25 (least of all steam) Set 16 (most of all steam) Parameter comparison Set No.* q [kw m^-2] G [kg m^-2s] T in [ C] P in [kpa] ANSYS, Inc. All rights reserved. 44 ANSYS, Inc. Proprietary

45 Model Parameter Modifications in Comparison to PWR Conditions Found that submodels need modifications for BWR conditions (see also Tu&Yeoh, Anglart et al., Krepper, Koncar): 1. Bulk bubble diameter Kurul & Podowski d B,max wall modified d B law d B,max wall 2. Bubble departure diameter Tolubinski & Kostanchuk const. bubble dept. diam. d W ~0.5mm max. d W =1mm - 3mm 3. A 2 - Wall area fraction influenced by steam bubbles default 0.5 increased up to ANSYS, Inc. All rights reserved. 45 ANSYS, Inc. Proprietary

46 Modification for Bulk Bubble Diameter Correlation Modified Kurul & Podowski (1991) law: d B = ( ) + ( ) d T T d T T B1 sub sub,2 B2 sub,1 sub T T sub,1 sub, ANSYS, Inc. All rights reserved. 46 ANSYS, Inc. Proprietary

47 Set25: Variation of Bubble Departure Diameter Tolubinski & Kostanchuk (1970) vs. const. bubble departure diameter d W =1,,3mm Measurement cross z = 1610 [mm] 2009 ANSYS, Inc. All rights reserved. 47 ANSYS, Inc. Proprietary

50 The RPI Wall Boiling Model: Lee et al. Testcase with CHT Specific energy source in solid material, Set25 (equiv. to q Wall ): E 7 3 Core = [W/m ] Temperature and Steam VF distribution in vertical plane 2009 ANSYS, Inc. All rights reserved. 50 ANSYS, Inc. Proprietary

51 The RPI Wall Boiling Model: Lee et al. Testcase with CHT Set25 & CHT: Grid independence for temperature z=1610[mm]; 1 1 mesh interface Heated Core Fluid Domain Unheated Cladding 2009 ANSYS, Inc. All rights reserved. 51 ANSYS, Inc. Proprietary

53 The RPI Wall Boiling Model: Lee et al. Testcase with CHT Comparison of temperature distributions for conforming vs. non-conforming mesh, 1 1 vs. GGI 2009 ANSYS, Inc. All rights reserved. 53 ANSYS, Inc. Proprietary

55 FRIGG-6a Test Case Description Geometry (FT-6a) Six electrically heated rods placed in a vertical adiabatic pipe Flow Parameters Upward directed subcooled water flow Mass G in = 1163 kg m -2 s -1 p in = 5 MPa Rod wall heat flux q Rod = MW m -2 Adiabatic Wall L H =4.2 m Heated Rod Liquid T sub = 4.5 K 2009 ANSYS, Inc. All rights reserved. 55 ANSYS, Inc. Proprietary

56 FRIGG-6a Test Case Experimental Data Determination of experimental data by gamma ray attenuation method: Measurements of area averaged gas volume fraction in different cross-sectional zones along the test section Defintion of Zones: r Zone1 Zone2 Zone3 Zone1 (r < 14.6 mm) Zone2 (14.6 mm < r < 28.6 mm) Zone3 (r > 28.6 mm) 2009 ANSYS, Inc. All rights reserved. 56 ANSYS, Inc. Proprietary

57 FRIGG-6a Test Case Mesh Refinement Hierarchy Mesh01 Mesh02 Mesh03 No. Elements 699 x 150 ( ) 2796 x 300 ( ) x 600 ( ) No. Nodes Max y Min Angle [deg] Min Determinant Numerical Effort ~ 90 6 CPU s ~ CPU s ~ 6 40 CPU s 2009 ANSYS, Inc. All rights reserved. 57 ANSYS, Inc. Proprietary

$of gas volume fraction (Mesh03, SST) Two cross-sectional$ $distributions of gas volume fraction (Mesh03,SST) 2009$

58 FRIGG-6a Test Case Baseline Setup: SST Outlet Outlet Plot of gas volume fraction (Mesh03, SST) Two cross-sectional distributions of gas volume fraction (Mesh03,SST) 2009 ANSYS, Inc. All rights reserved. 58 ANSYS, Inc. Proprietary

cross-sectional distributions of liquid temperature

59 FRIGG-6a Test Case Baseline Setup: SST Outlet Outlet Plot of liquid temperature (Mesh03,SST) Two cross-sectional distributions of liquid temperature (Mesh03,SST) 2009 ANSYS, Inc. All rights reserved. 59 ANSYS, Inc. Proprietary

63 Turbulence Modeling in Rod Bundles So far good comparison, but Wall friction in rod bundles leads to secondary flows Anisotropic flow and turbulence SST BSL RSM Does not influence so much cross-sectional averaged flow properties Secondary flows affect steam & temperature distributions on wall surfaces Can be relevant for safety! 2009 ANSYS, Inc. All rights reserved. 63 ANSYS, Inc. Proprietary

$Outlet Plot of gas volume fraction 2009$

$fraction (Outlet) Contour$ (Outlet) 2009 ANSYS, Inc.

69 FRIGG-6a Test Case Turbulence Model Comparison SST model NO secondary flows Plot of gas volume fraction (Outlet) Contour plot of gas volume fraction (Outlet) 2009 ANSYS, Inc. All rights reserved. 69 ANSYS, Inc. Proprietary

$model secondary flows Plot of gas volume fraction$ $(Outlet) Contour plot of gas volume fraction (Outlet)$

70 FRIGG-6a Test Case Turbulence Model Comparison BSL RSM model secondary flows Plot of gas volume fraction (Outlet) Contour plot of gas volume fraction (Outlet) 2009 ANSYS, Inc. All rights reserved. 70 ANSYS, Inc. Proprietary

71 New R&D Consortium R&D Initiative: Modeling, Simulation & Experiments for Boiling Processes in Fuel Assemblies of PWR ANSYS Germany Karlsruhe Inst. of Technology (KIT) FZ Dresden/ Rossendorf TUM, Dept. Thermodynamics Univ. Bochum, Dept. Energy Systems 2009 ANSYS, Inc. All rights reserved. TUD, Dept. Fluid Mechanics 71 TUD, Dept. Nucl. Eng. TUD Medical Faculty Univ. Appl. Sciences Zittau/ Görlitz ANSYS, Inc. Proprietary

72 Modeling, Simulation & Experiments for Boiling Processes in Fuel Assemblies of PWR Ultrafast electron beam X-ray CT of fuel rod bundle in titanium pipe on FZD: Images by courtesy of U. Hampel, FZD 2009 ANSYS, Inc. All rights reserved. 72 ANSYS, Inc. Proprietary

rod bundle with spacer grid: Wall superheat T W -T Sat

73 Modeling, Simulation & Experiments for Boiling Processes in Fuel Assemblies of PWR Wall boiling simulation in a 3x3 rod bundle with spacer grid: Wall superheat T W -T Sat 2009 ANSYS, Inc. All rights reserved. 73 ANSYS, Inc. Proprietary

74 Summary & Outlook Overview on ANSYS CFD boiling model development and validation Continuous effort in model improvement, R&D Emphasis in validation on BPG, comparison to data, geometry & grid independent modeling Complex MPF phenomena number of uncertainties remaining for further investigations detailed experiments Outlook: Ongoing & customer driven CFD model development Research cooperation with Industry & Academia Coupling of wall boiling model to inhomogeneous MUSIG Extension of the wall heat partitioning in wall boiling model 2009 ANSYS, Inc. All rights reserved. 74 ANSYS, Inc. Proprietary

CFD-Modeling of Boiling Processes

CFD-Modeling of Boiling Processes 1 C. Lifante 1, T. Frank 1, A. Burns 2, E. Krepper 3, R. Rzehak 3 conxita.lifante@ansys.com 1 ANSYS Germany, 2 ANSYS UK, 3 HZDR Outline Introduction Motivation Mathematical