Cfd 71c3k

Extensible Volume-of-Fluid Solver for Phase-Change Heat Transfer

Computational Fluid Dynamics Basuraj Shyam, Sumit Zanje

BITS Pilani

Need for Phase Change Simulation Tools  Steam generation: 41% of primary energy,72% rejected to ambient through condensation  Phase change is often efficiency bottleneck,analytic solutions only for simplest configurations  Need robust simulation tools for diverse phase change processes in emerging enhanced geometries

Enhanced Condenser

Enhanced Boiling

(Wieland Group, 2013)

(Cooke and Kandlikar,2011) 2

Interface Capturing Standard approach: couple energy equation and phase change Formulations source with adiabatic flow formulation

Interface Capturing Standard approach: couple energy equation and phase

Formulations

SaturateInterfac Empirical Paramet Adapted ′′′ � − ′′′ = ℎ � − sat � ′′′ = �1 − � 1 V PC = � �PC change source with adiabatic flow � sat � PC d e ∆� Rate er �sat Correlation � �

formulation

�

�

�

�sat

�p

Film Bubble

condensation

−

•

Need for Extensible Phase Change Prior formulations fit in

Solver

• common

framework: source

whole new solver

energy equation & phase – Repeated development and validation

efforts change – Limited code but, nearly allavailability studies and maintenance implement Project goal: Implement flexible VOF-based

for

solver diverse phase-change heat transfer processes “Common framework for phase change 5

•

VOF Phase Change VOF Phase

solver

u Solver  i

Continuit

change

y Phas e

 t



 xi

v PC

  xi  u i

on interFoa

Momentu

based

 

PC

m Energ y

Overvie

 h

t

w

 ui   u  ui p     j t  xj  xi

m

2

eff

i

 u

 x i x j

 f

i

T       q P C u h     i  xi  xi  k e f f  xi   

• Selectable f (Brackbill et al., 1992; Raeini et al., σ • fluid property calculation (Marschall et 2012 2012) • Selectable al.,

)

Multistep method implemented for energy equation 6

Phase Change Solver Algorithm

α

qPC 7

T

thermalPhaseChangeModel •

Phase change models extend

Class

• thermalPhaseChangeModel

•

– (Similar turbulence Q_pc()to (heat source) models) – Must implement: (dilatation, default – PCV() available) source, default alpha1Gen() (liquid volume available) fraction

Implementations – Interface equilibrium (Rattner and Garimella, – for: – 2014) – Empirical rate parameter (Yang et al., 2008) 8

Example Phase Change Model •

Empirica rateparamete model (Yanget al., 2008 Implementation

//Evaluates phase change heat source term field void Foam::thermalPhaseChangeModels::Yang::calcQ_pc() { l dimensionedScalar& r ) const rhol = twoPhaseProperties_.rho1(); const dimensionedScalar& rhov = twoPhaseProperties_.rho2(); Q_pc_ = pos(T_-T_sat_)*h_lv_*rl*alpha1_*rhol *((T_-T_sat_)/T_sat_) + neg(T_-T_sat_)*h_lv_*rv*(1.0-alpha1_)*rhov *((T_-T_sat_) / T_sat_); } //Updates model parameters from specified input file bool Foam::thermalPhaseChangeModels::Yang::read( const dictionary& thermalPhaseChangeProperties) { thermalPhaseChangeModel::read(thermalPhaseChangeProperties); thermalPhaseChangeProperties_.lookup("rl") >> rl; thermalPhaseChangeProperties_.lookup("rv") >> rv; return true; }

9

Validatio Cases Horizontal

•Film

Smooth Falling Film

n

(1)

•Evaporation / Error < 1.2%

Linear = 0.36∆1.05 (� condensatio convergence ) n

large

rang of grids Condensation over Heat Flux Relative Error e

Heat Flux (kw m-2)

20

5

10

Cell Size (μm)

16

15

0. 0. 0. 0. 0. 0. 020 016

12

012

8

008

4

004

0

000 0

10

Validatio Cases Rising Bubble • h agreement: n bub Condensation 5.6%

Single droplet • (2) Interfacial resistance condensation • model needed for -line PC 3% radius change error during growth

11

Scaling

• Model problem: Falling film absorption • Performance MPI-based domain decomposition parallelization 12

Application: Wavy Film Phase

• 2D simulations of wavy falling film heat • Change

First studie to measur effectof σ on heat transfe transfer s

e

r

13

Applications: Dropwise

• High heat flux condensation mode on non-wetting Condensation surfaces (10× filmwise): promising for • power plant model drops as rigidparticle (no Previous applications studies

s

dynamics)

14

•

Applications: Nucleate In boiling, phase change primarily occurs in

Boiling

• bubbles • growing from imperfections in surface Analytical theory limited to individual bubbles In practice: strongly interacting nucleation sites

15

•

Applications: Taylor Flow Simulation of coupling-fluid-heated

Evaporation

• evaporating Taylor flow Informed new wake-region heat transfer model

•

Summar interThermalPhaseChangeFoam: Extensible

y

• solver •

for liquid-vapor phase change processes

Runtime selectable phase-change • models: Yang et al., 2008; Kunkelmann & Stephan, 2009; Rattner & Garimella, 2014

Validation cases for: •

Stefan problem, Nusselt problem, wavy film heat transfer, rising bubble condensation, droplet condensation on surface

Solver, libraries, tutorials, validation test

Applications in:

wavy film HT, dropwise condensation,

nucleate boiling,

scripts @

17

•

ThankYou Sponsors :

•

Solver

and tutorials

@

code https://github.com/MahdiNabil/CFDavailable PC

(OpenFOAM libraries V2.4.0) Alexander S

18