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CFD Modeling of Heat
Transfer, Boiling and
Condensation
NUFOAM & NUMPOOL
Presented by Juho Peltola, VTT
SAFIR2014 Final Seminar, 19.3.2015, Espoo
Projects
NUFOAM: OpenFOAM CFD solver in nuclear reactor
safety applications (2011-2014)
VTT1, Aalto University2, LUT3 and Fortum 4
Juhaveikko Ala-Juusela2, Tomas Brockmann2, Karoliina Ekström4, Giteshkumar Patel3,
Juho Peltola1, Timo Pättikangas1, Timo Siikonen2, Vesa Tanskanen3, Timo Toppila4
Single-phase turbulence and heat transfer
Two-phase flow with boiling and condensation
NUMPOOL: Numerical modelling of condensation pool
VTT: Timo Pättikangas, Jarto Niemi, Antti Timperi, Qais Saifi
CFD modeling of condensation of steam in the pressure
suppression pool of BWR
Fluid-Structure Interaction calculations of the pressure loads
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OpenFOAM?!
An open-source CFD toolbox released by OpenFOAM
Foundation.
A collection of C++ modules that allow development of
simulation tools for different purposes
Unstructured, polyhedral, 3D FVM
Continuum 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 with
OpenFOAM!
OpenFOAM 1.7.x (2010) twoPhaseEulerFoam:
Euler-Euler solver for turbulent two-phase flows
Constant material properties
Constant dispersed phase diameter
No heat or mass transfer
No bubble specific drag models
No turbulent dispersion or wall lubrication force
Hard-coded k- turbulence model
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OpenFOAM and Subcooled Nucleate Boiling
In 2011-2012 we developed an OpenFOAM based solver that
addressed most of the weaknesses:
”twoPhaseNuFoam v0.4:”
Euler-Euler solver for turbulent two-phase flows
Non-uniform material properties
Models for local bubble diameter
Support for mass transfer between the phases
Enthalpy based heat transfer solution, with interfacial boiling and
condensation
RPI wall boiling model
Runtime selectable framework for interfacial force models
A selection of relevant drag, lift, aspect ratio, turbulent dispersion and wall
lubrication force models
Hard-coded k- or kturbulence models
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…
SST turbulence models, with optional bubble induced
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OpenFOAM and Subcooled Nucleate Boiling
At the same time, active development of the two-phase solver of the official
OpenFOAM started after a few dormant years:
2.1.0: 2011: Temperature based heat transfer solution, compressibility, nonuniform diameter
2.1.1: 2012: Improved void fraction solution algorithm (MULES)
2.2.0: 2013: Support for multiphase thermodynamics, enthalpy based energy
solution
2.3.0: 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 official
OpenFOAM release
Maintainability, improved capability, efficient international cooperation 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 the
applied combination interfacial and turbulence
models.
It is important to find robust model combinations
that behave reasonably well in wide range of
cases.
Presented test case: DEDALE 11-01 vertical
bubbly pipe flow
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twoPhaseNuFoam v0.6: Simulation Examples:
Subcooled Nucleate boiling
Presented test case: DEBORA5, Vertical R-12 pipe
flow.
Good results were obtained with the kturbulence model.
SST
Poor results were obtained with the std. kturbulence model.
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Dispersed Eulerian Approach In Complex
Geometries
Interface capturing (VOF)
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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 bundle
Rod pitch:
Gap between rods:
Bubble diameter:
34 mm
9 mm
3.8 mm
Void distribution and
influence of the spacer
grid are still well
predicted.
At least when bubbles are
relatively small.
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OpenFOAM and Subcooled Nucleate Boiling:
Conclusions and Outlook
Two generations of OpenFOAM based subcooled nucleate boiling
capable 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 OpenFOAM
release.
Provide a commonly available, transparent software platform
for international co-operation in further development of the
boiling and condensation model.
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Modeling of BWR pressure suppression pool
(NUMPOOL)
Postulated Large-Break Loss-Of-Coolant-Accident (LBLOCA) in a BWR is
studied with CFD and FEM calculations.
Steam released into the drywell compartment is blown into the pressure
suppression pool.
Containment of a
Nordic BWR
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CFD model for a 90° sector
of BWR drywell and wetwell
CFD modelling for
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PPOOLEX experiments
Early phase of Large-Break Loss-Of-CoolantAccident (LBLOCA)
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t = 1.0 s
t = 1.3 s
t = 1.6 s
t = 2.2 s
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FSI calculations of PPOOLEX experiments
Fluid-Structure Interaction (FSI) simulations were performed for the
calculation 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 were
carried out
Non-condensable early phase in a realistic BWR containment was
also simulated.
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FSI calculations of PPOOLEX experiments:
Comparison with air discharge experiment
t = 1.63 s
1.74 s
1.84 s
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Star-CD
Star-CCM+
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Stochastic pressure loads from vent pipes
A typical Nordic BWR has 16 vent pipes, which form large steam
bubbles during blowdown.
The steam bubbles do not collapse simultaneously.
• The desynchonization of the rapid condensation events was studied
experimentally in the EXCOP project with the PPOOLEX test facility.
• Data is also publicly available from JAERI experiments performed with a
sector model of MARK-II containment.
The statistical behaviour of condensation events was deduced
from experimental data.
The pressure loads and displacements of a BWR containment
were studied with the acoustic model of the ABAQUS code.
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Stochastic pressure loads from vent pipes:
Calculated wall displacements
RMS and maximum
0.5
Pipe
Pipe
Pipe
Pipe
Pipe
Pipe
Pipe
Pipe
Pipe
Pipe
Pipe
Pipe
Pipe
Pipe
Pipe
Pipe
Amplitude
Amplitude
0
-0.5
-1
0
0.5
1
1.5
2
2.5
3
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
3.5
displacements
RMS displacement
Gas in the water pool affects the local speed
of sound.
Two different constant speeds of sound
were considered.
Asynchronous cases produce loads approx.
30% lower than a synchronized case.
1
0,9
0,8
0,7
0,6
0,5
0,4
0,3
0,2
0,1
0
Case 1
4
Case 2
Case 3
Case 4
4.5
Time
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Time (s)
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NUMPOOL conclusions
The early phase of LBLOCA can be fairly well calculated with CFD codes.
Models for the condensation of vapor in drywell have been developed and
implemented successfully in a CFD code.
Modeling direct-contact condensation of vapor with CFD codes is not yet
accurate enough for the determination of pressure loads.
Acoustic FEM models with pressure sources obtained from experiments
can 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.
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Thank you for your attention!
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