CFD Modeling of HeatTransfer, Boiling andCondensationNUFOAM & NUMPOOLPresented by Juho Peltola, VTTSAFIR2014 Final Seminar, 19.3.2015, Espoo

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Projects

NUFOAM: OpenFOAM CFD solver in nuclear reactorsafety applications (2011-2014)

VTT1, Aalto University2, LUT3 and Fortum4

Juhaveikko Ala-Juusela2, Tomas Brockmann2, Karoliina Ekström4, Giteshkumar Patel3,Juho Peltola1, Timo Pättikangas1, Timo Siikonen2, Vesa Tanskanen3, Timo Toppila4

Single-phase turbulence and heat transferTwo-phase flow with boiling and condensation

NUMPOOL: Numerical modelling of condensation poolVTT: Timo Pättikangas, Jarto Niemi, Antti Timperi, Qais Saifi

CFD modeling of condensation of steam in the pressuresuppression pool of BWRFluid-Structure Interaction calculations of the pressure loads

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OpenFOAM?!

An open-source CFD toolbox released by OpenFOAMFoundation.

A collection of C++ modules that allow development ofsimulation tools for different purposes

Unstructured, polyhedral, 3D FVMContinuum mechanics, particle tracking, radiation,chemistry…

Widely used by academics and industry

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OpenFOAM and Subcooled Nucleate Boiling

2011: We want to simulate subcooled nucleate boiling withOpenFOAM!

OpenFOAM 1.7.x (2010) twoPhaseEulerFoam:Euler-Euler solver for turbulent two-phase flowsConstant material propertiesConstant dispersed phase diameterNo heat or mass transferNo bubble specific drag modelsNo turbulent dispersion or wall lubrication forceHard-coded k- turbulence model

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OpenFOAM and Subcooled Nucleate Boiling

In 2011-2012 we developed an OpenFOAM based solver thataddressed most of the weaknesses:

”twoPhaseNuFoam v0.4:”Euler-Euler solver for turbulent two-phase flowsNon-uniform material propertiesModels for local bubble diameterSupport for mass transfer between the phasesEnthalpy based heat transfer solution, with interfacial boiling andcondensationRPI wall boiling modelRuntime selectable framework for interfacial force modelsA selection of relevant drag, lift, aspect ratio, turbulent dispersion and walllubrication force modelsHard-coded k- or k- SST turbulence models, with optional bubble inducedturbulence models…

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OpenFOAM and Subcooled Nucleate Boiling

At the same time, active development of the two-phase solver of the officialOpenFOAM started after a few dormant years:

2.1.0: 2011: Temperature based heat transfer solution, compressibility, non-uniform diameter

2.1.1: 2012: Improved void fraction solution algorithm (MULES)2.2.0: 2013: Support for multiphase thermodynamics, enthalpy based energy

solution2.3.0: 2014: Consolidation, new runtime selectable interfacial and turbulence

models. Large selection of closure models.2.3.1: 2014: Re-formulated as fully conservative for mass, momentum and

energy.

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OpenFOAM and Subcooled Nucleate Boiling

CONCLUSION (2013): Not resource efficient to maintain a separate fork!

Re-write, re-test with the goal to integrate with the officialOpenFOAM releaseMaintainability, improved capability, efficient international co-operation and improved validation.

twoPhaseNuFoam v0.6 = OpenFOAM 2.3.1 twoPhaseEulerFoam+ Bug fixes+ Modified interfacial force treatment+ Extended model selection+ Thermal wall functions+ Two-resistance interfacial heat transfer+ Wall boiling and interfacial condensation.

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twoPhaseNuFoam v0.6: Simulation Examples:Interfacial Forces and Turbulence

Radial void distribution is highly sensitive to theapplied combination interfacial and turbulencemodels.It is important to find robust model combinationsthat behave reasonably well in wide range ofcases.Presented test case: DEDALE 11-01 verticalbubbly pipe flow

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twoPhaseNuFoam v0.6: Simulation Examples:Subcooled Nucleate boiling

Presented test case: DEBORA5, Vertical R-12 pipeflow.Good results were obtained with the k- SSTturbulence model.Poor results were obtained with the std. k-turbulence model.

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Dispersed Eulerian Approach In ComplexGeometries

Interface capturing (VOF) Dispersed Eulerian (two-fluid)

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twoPhaseNuFoam v0.6: Simulation Examples:Influence of a spacer grid

Presented test case:SUBFLOW(Ylönen, 2013; Hyvärinen, 2014)

Isothermal rod bundleRod pitch: 34 mmGap between rods: 9 mmBubble diameter: 3.8 mm

Void distribution andinfluence of the spacergrid are still wellpredicted.

At least when bubbles arerelatively small.

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OpenFOAM and Subcooled Nucleate Boiling:Conclusions and Outlook

Two generations of OpenFOAM based subcooled nucleate boilingcapable solvers have been developed and tested.

The latest version is based on OpenFOAM 2.3.1 twoPhaseEulerFoam.

The next step:

Increase co-operation with the OpenFOAM Foundation

Integrate the boiling capability into the official OpenFOAMrelease.

Provide a commonly available, transparent software platformfor international co-operation in further development of theboiling and condensation model.

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Modeling of BWR pressure suppression pool(NUMPOOL)

CFD modelling forPPOOLEX experiments

Containment of aNordic BWR

CFD model for a 90° sectorof BWR drywell and wetwell

Postulated Large-Break Loss-Of-Coolant-Accident (LBLOCA) in a BWR isstudied with CFD and FEM calculations.Steam released into the drywell compartment is blown into the pressuresuppression pool.

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t = 1.0 s t = 1.3 s

t = 1.6 s t = 2.2 s

Early phase of Large-Break Loss-Of-Coolant-Accident (LBLOCA)

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Fluid-Structure Interaction (FSI) simulations were performed for thecalculation of loads & structural response

Two-way coupling of Star-CCM+ CFD & Abaqus FEM codes

CFD-FEM calculations were first verified against acoustic FEM

FSI simulations of PPOOLEX experiment with air discharge werecarried out

Non-condensable early phase in a realistic BWR containment wasalso simulated.

FSI calculations of PPOOLEX experiments

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t = 1.63 s

1.74 s

1.84 sStar-CD Star-CCM+

FSI calculations of PPOOLEX experiments:Comparison with air discharge experiment

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A typical Nordic BWR has 16 vent pipes, which form large steambubbles during blowdown.The steam bubbles do not collapse simultaneously.

• The desynchonization of the rapid condensation events was studiedexperimentally in the EXCOP project with the PPOOLEX test facility.

• Data is also publicly available from JAERI experiments performed with asector model of MARK-II containment.

The statistical behaviour of condensation events was deducedfrom experimental data.The pressure loads and displacements of a BWR containmentwere studied with the acoustic model of the ABAQUS code.

Stochastic pressure loads from vent pipes

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00,10,20,30,40,50,60,70,80,9

1

Case 1 Case 2 Case 3 Case 4

RM

Sdi

spla

cem

ent

Gas in the water pool affects the local speedof sound.Two different constant speeds of soundwere considered.Asynchronous cases produce loads approx.30% lower than a synchronized case.

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5

-1

-0.5

0

0.5

Time

Am

plitu

de

Pipe 1Pipe 2Pipe 3Pipe 4Pipe 5Pipe 6Pipe 7Pipe 8Pipe 9Pipe 10Pipe 11Pipe 12Pipe 13Pipe 14Pipe 15Pipe 16

Time (s)

Ampl

itude

RMS and maximumdisplacements

Stochastic pressure loads from vent pipes:Calculated wall displacements

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The early phase of LBLOCA can be fairly well calculated with CFD codes.

Models for the condensation of vapor in drywell have been developed andimplemented successfully in a CFD code.

Modeling direct-contact condensation of vapor with CFD codes is not yetaccurate enough for the determination of pressure loads.

Acoustic FEM models with pressure sources obtained from experimentscan be used for calculating the loads caused by rapid condensation.

FSI calculations for the pressure loads have been performed.

Desynchronization of the vent pipes reduces the pressure loads.

NUMPOOL conclusions

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Thank you for your attention!