1

Modelling of two-phase boiling flows with OpenFOAM-SIAMUF seminar

Kai Fu

Division of Nuclear Reactor Technology, KTH

May 24, 2012

2

ObjectiveProject Northnet Roadmap 1: Development of two phase flow with OpenFOAM

Model descriptionGoverning equation and closure laws

Validation case2D/3D uniform heated pipe

Future work

Outline

3

Problem description in subcooled two-phase flow

qw' '

Onset of nucleate boiling

Modeling of1. bubble lift off size2. evaporation rate at walls3. condensation rate in the bulk4. bubble movement/distribution

Prediction/validation:1. void fraction2. bubble diameter3. velocities4. liquid temperature

4

Objective - Northnet Roadmap 1: Development of two phase flow with OpenFOAM

Why OpenFOAM open source free distribution rather fast growing user base

ANSYS

CD-adapco

CFdesign

Edge

FLOW-3D

NUMECA

OpenFOAM

Phoenics

0 50,000 100,000 150,000 200,000

Posts at cfd-online forum

~ March 2010

5

Objective - Northnet Roadmap 1

Mechanistic modeling of two-phase flows and heat transferin fuel assemblies of LWRs in Eulerian method1. wall heat partitioning model 2. interfacial area transport model3. interfacial momentum transfer4. turbulence modeling in two-phase flow5. applicable for both steady-state and transient analyses in 3D geometries6. prediction of onset of critical heat flux

Validation of implemented models 1. adiabatic air-water upward bubbly flow2. subcooled wall boiling two-phase flow

6

Model description

Phase continuity equation

Linear momentum conservation equation

M ki Interfacial momentum transfer

drag force, lift force, wall lubrication force, turbulent dispersion force,virtual mass force

7

Enthalpy equation

l

ev Cells adjacent to walls

Other cells=

qw=q1qeqq

Interfacial heat transfer

Wall boilingAt near wall cells: wall heat partitioning model

Other cells in the bulk: interfacial heat transfer

Nu=20.6Re0.5Pr0.33

qw=q1qeqq

Model description

8

Interfacial area concentration transport equation

BB

BC Random collision, wake entrainment

Turbulence induced

Hibiki and Ishii: air/water adiabaticYao and Morel: improved version, DEBORA exp

Lo, Rao and Zhang: S-Gamma model, droplets/bubbles

ai=6DS

Model description

9

Upward pipe flow validation case 1: Bartolomej experiment

Working fluid

p (MPa) G (kg/m2s) qw (kW/m2) Tsub (K)

water 4.5 900 570 58.2

10

Upward pipe flow validation case 2: DEBORA experiments

Working fluid

p (MPa) G (kg/m2s) qw (kW/m2) Tsub (K)

R12 1.4/2.6 1980-2980 74-109 17.5-23.4

Void fraction

11

Void fraction (continued)

Upward pipe flow validation case 2: DEBORA experiments

Working fluid

p (MPa) G (kg/m2s) qw (kW/m2) Tsub (K)

R12 1.4/2.6 1980-2980 74-109 17.5-23.4

12

Liquid temperature

Upward pipe flow validation case 2: DEBORA experiments

Working fluid

p (MPa) G (kg/m2s) qw (kW/m2) Tsub (K)

R12 1.4/2.6 1980-2980 74-109 17.5-23.4

13

Bubble size

14

Future work

Extension of validation case: 3D

1. Validation of mechanistic wall heat partitioning model in a low void fraction (<1%) subcooled flow

2. part of the rod bundles.

aθ

n

t

FSTn

FSTt

FGRt

FGRn

FS

FQS

FP

FG

y

xrθ

iθ

Situ and Hibiki, 2005

Bubble departure: 0, =ttotF

Bubble lift off: 0, =ntotF

15

Thanks!