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WP2.2: Boiling flow andDeparture from Nucleate Boiling
D. Bestion, C. Morel, S. Mimouni, E. Krepper, A. Badillo, Y. Sato, B. Niceno, M. C. Galassi, A. Del
Nevo, F. Moretti, B. Koncar , M. Matkovič, L. Vyskocil, J. Macek, D. Tar , G. Mayer, G. Hazi, A.
NURISP SEMINARApril2-3, Karlsruhe
1
Vyskocil, J. Macek, D. Tar , G. Mayer, G. Hazi, A. Markus
OBJECTIVES
1. Better understanding of local flow processes in boiling flow
– non-uniform heat flux– grid effects, – channel shape/size impact
2. Improvement of the subchannel approach– decrease of conservatisms through more general
and accurate CHF correlations
NURISP SEMINARApril2-3, Karlsruhe
2
3. Help for design/optimization of fuel assemblies– parametric studies on design– optimization of CHF test procedures, reduction of
CHF tests
4. Development of a CHF “Local Predictive Approach”
– DNB correlations based on local parameters instead of cross-sectional averaged parameters
type 1 type 2 type 3
type 4 type 5
type 6
MULTI-SCALE ANALYSIS OF DNB
DNSLBM, VOF, LS PF
NucleationBubble detachment
Separate Effect Testsadiabatic
Air –water & steam-waterDEDALE, LiNX, TOPFLOW
CHAPTAL
CFD models
Rod Bundle tests
KFKI, BFBT, PSBT, LWL
modeling M
odel
ing
valid
atio
n
validationvalidation
ModelingSubchannel codes
DNSLBM, VOF, LS PF
NucleationBubble detachment
Separate Effect Testsadiabatic
Air –water & steam-waterDEDALE, LiNX, TOPFLOW
CHAPTAL
CFD models
Rod Bundle tests
KFKI, BFBT, PSBT, LWL
modeling M
odel
ing
valid
atio
n
validationvalidation
ModelingSubchannel codes
NURISP SEMINARApril2-3, Karlsruhe
3
CFD models• LES
•RANS
Separate Effect TestsBoiling flow
ASU, DEBORA, TESS
Modeling
Fuel design
Modeling
validation
Subchannel codes
CHF prediction
CFD models• LES
•RANS
Separate Effect TestsBoiling flow
ASU, DEBORA, TESS
Modeling
Fuel design
Modeling
validation
Subchannel codes
CHF prediction
CFD MODELLING OF BOILING FLOW
Identification of important flow processes
Exp. Data BASIS+ DNSMODEL OPTIONS
NURISP SEMINARApril2-3, Karlsruhe
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CLOSURE LAWS
+ DNSMODEL OPTIONS– Nb of fields– Space and time resolution
SET OF EQUATIONS
CFD MODEL OPTIONS FOR DNB
� RANS is OK ; no added value with LES� 2-Fluid at least necessary to model all interfacial forces� Turbulence modeled by k-ε, SST, or Rij-ε� Efforts to predict bubble diameter:
� Monodispersed assumption: transport of n or Ai� Polydispersion modeling by:
NURISP Mid-term Review Meeting, October 7 th, 2010 - BRUSSELS:Progress of SP2 activity at Mid-term
5
� Polydispersion modeling by:• MUSIG approach• MSM (statistical moments)
� Main efforts devoted to:� Interfacial forces & H&M transfers� Wall transfers : momentum, energy, DNB criterion� 2-phase effects on turbulence� polydispersion
Interfacial forces
Drag force :
Lift force :
Added Mass force :
( )lglgDliDl
Dg VVVVCa
8
1MM
vvvvvv−−ρ−=−=
∇⋅+∂
∂−
∇⋅+
∂∂
ρα−α+α−=−= ll
lgg
glMA
MAl
MAg VV
tV
VVt
V
121
CMMvv
vvv
vvv
L
TD
NURISP SEMINARApril2-3, Karlsruhe
6
Lift force :
Turbulent Dispersion force :
( ) ( )lT
llglLLl
Lg VVVVCMM
vvvvvv∇−∇⋅−αρ−=−=
α∇ρ−=−= llDTDTl
DTg KCMM
vv
+ possibly a Wall lubrication force
CL may change sign when size increases (Tomiyama)
D
WB
Wall heat transfer & Interfacial heat transfers
Convection :
Vaporization :
Quenching :
( )lwcc TThAq −= log +=T
uCh pll
*
log ρ
( )lwlqqq
ta
TTftAq
πλ −= 2
LNd6
fq g3
nuce ρπ=
Models required for f, dnuc, & N
NURISP SEMINARApril2-3, Karlsruhe
7
Quenching :ql
qqqta
ftAqπ
=
Liquid to Interface heat transfer
( )lsatilili TTahq −=
Nud
hs
lli
λ= 33.05.0 PrRe6.02 +=Nu
Turbulence models
• Sato (1981): turbulence viscosity of the liquid phase + Increasing of the liquid viscosity by bubbles:
• Sources and sinks in turbulent equations
6.0=SC LGGLSL UUCk
Crr
−++= αρε
ρµµ µ
2
( ) ( ) kturbl SPkkvk +−+
∇⋅∇=⋅∇+∂ ερµαραρα v
NURISP SEMINARApril2-3, Karlsruhe
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( ) ( ) klllll
k
lllllllll SPkkvk
t+−+
∇⋅∇=⋅∇+
∂∂ ερ
σµαραρα v
LGgd
kkl UUFS
rrv−⋅−= α
( ) ( ) ( ) εεε
ε
ερεεσ
µαεραερα lllll
ll
turbl
llllllll SCPCk
vt
+−+
∇⋅∇=⋅∇+
∂∂
21
v
τεε
kl
l
SCS 3=ε
ρµ µ
2kCT =
Bubble diameter in monodispersed approachBubble diameter in monodispersed approach
Bubble number density :
Interfacial area density :
( ) BK
n
Coal
n
Coll
n
Nuc
nnVndiv
t
n φφφφ +++=+∂∂ v
63sd
nπ
α=with :
NURISP SEMINARApril2-3, Karlsruhe
9
Interfacial area density :
6
63
i
sa
dα=with :
( ) BK
a
Coal
a
Coll
nColl
Nuc
nnuc
g
ig
g
i
ii
i
iidd
dt
daVadiv
t
a φφφπφπρ
ααρ
++++
−Γ=+∂∂ 22
,3
2v
BK
n
i
BK
a
CO
n
i
Coal
a aa iiφαπφφαπφ
22
3
36
3
36
=
=
Data base for DNB
visualisations
Boiling flow Simple geometry
LWL BFBT, PSBT
Boiling flowreactor geometry
CHF testsreactorgeometry
NURISP SEMINARApril2-3, Karlsruhe
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Adiabatic bubbly flow
DedaleTopflow
DeboraASU
Boiling flow Simple geometry
Turbulencepromoter
AGATE
KFKI
Review about DNB mechanisms and models
1. Hydrodynamic instability (e.g. Zuber, 1958)2. Leidenfrost T°reached (e.g. Unal, 1992; Bricard, 1995; Le Corre, 2007)3. Dry spot spreading (e.g. Unal, 1992; Bricard, 1995; Ha & No, 2000; Le Corre, 2007)4. Macro-layer vaporization (e.g. Haramura, 1983; Celata, 1994; He, 2001)5. Micro-layer vaporization (Zhao, 2002), 6. Recoil force instability (Beysens, 2003); 7. Micro-layer rupture (Théofanous, 2002)
CEA
NURISP SEMINARApril2-3, Karlsruhe
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Conclusion of the review
� No local DNB criterion for CFD for convective boiling
� No consensus on the DNB mechanism itself
� The very simple switch to film boiling based on a limiting void fraction (NEPTUNE) performs not so bad compared to existing models but is not sufficiently precise
� Two different & complementary ways are proposed for future
CEA
NURISP SEMINARApril2-3, Karlsruhe
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� Two different & complementary ways are proposed for future activities regarding the DNB prediction by CFD:– Long term activity: identification of the DNB mechanism using new
experiments and the use of DNS simulations– Short term activity: establish a semi-empirical local DNB criterion
with some free parameters to fit on tube CHF data. Then this DNB criterion could be confronted to a large data base including CHF in complex geometry.
Direct Numerical Simulation of Boiling
Numerical Method
• Navier-Stokes solver : PSI-BOIL
- Finite Volume method on Cartesian grids
- Projection method
• Interface tracking method
CIP-CSL2 (color function) with
Phase change rate (kg/m3s):
S
V
lq
vq
PSI
NURISP SEMINARApril2-3, Karlsruhe
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local interface sharpening scheme
• Phase change model
Sharp Interface Model
• Features
- Mass conservative scheme
- Simple phase change model
Phase change rate (kg/m3s):
l vq q Sm
L V
+=&
Latent heat Cell volume
Interface area
Heat fluxes
Verification: 3D Bubble Growth in Superheated Liquid
• Condition of simulation- Water and steam at 1 bar - Liquid superheat 5 C°- Unbounded domain -Thermal boundary layer: about 10 µm - Grid size: 8µm (Coarse), 4µm (Medium), 2µm (Fine)
0.0002
PSI
NURISP SEMINARApril2-3, Karlsruhe
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Time (s)
Rad
ius
(m)
0 0.0001 0.0002 0.00030
5E-05
0.0001
0.00015
AnalyticalCoarseMediumFine
Validation: Saturated Pool Boiling
EXP.*
Water at 1 (bar), Wall superheat = 9.44 (K), Contact angle =47°PSI
NURISP SEMINARApril2-3, Karlsruhe
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0.000 (s) 0.006 (s) 0.016 (s) 0.043 (s)
0.0007 (s) 0.006 (s) 0.016 (s) 0.045 (s)
PSI-BOIL
*: R. Siegel, E.G. Keshock, Effects of reduced gravity on nucleate boiling bubble dynamics in saturated water, AIChE J., 10 (1964) 509-517.
106.0105.6105.2104.8104.4104.0103.7103.3102.9
Sample Calculation: Subcooled Pool Boiling
Hea
tflu
x(W
/m2 )
0 0.1 0.2 0.3 0.4
10000
15000
20000
SaturatedSubcooled
Time (s)
Water at 1 (bar), Wall superheat = 6.17 (K) , Contact angle =38° PSI
NURISP SEMINARApril2-3, Karlsruhe
16Saturated boiling Subcooled boiling (97℃)
102.9102.5102.1101.7101.3100.9100.5100.1
99.799.399.098.698.297.897.497.0
Motivation:– key parameters of CHF are based on simple theoretical considerations (e.g. force balance
calculations) – for the application of theories the problem has to be oversimplified– numerical simulation can be used to approach real situations
Objective: to determine the functional relationship between thermophysical, geometrical parameters and the bubble detachment diameter, bubble release frequency taking into account more and more realistic situations
αα -- modelmodel ββ -- modelmodel γγ -- modelmodel
Use of LBM for boiling simulations
KFKI
NURISP SEMINARApril2-3, Karlsruhe
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αα -- modelmodel
P, P, TsatTsat
periodicperiodic
nono--slipslip
ββ -- modelmodel
P, P, TsatTsat
periodicperiodic
nono--slipslip
γγ -- modelmodel
P, P, TsatTsat
periodicperiodic
nono--slipslip
heat conduction in the wall heat conduction in the wall + cavity in the wall
P, P, TsatTsat
periodicperiodic
nono--slipslip
interaction between cavities
� without cavity and without heat conduction in the wall, simple theories work fine ( )gl
b gD
ρρσ−
~( ) 4/1
21 ~
−−
−
l
glb
gDf
ρρρσ
� Db vs. g � power function (exponents depends on the heating method, part of the heat escapes by natural convection)
� Db vs. θ� linear trend (slope lower with cavities)
� Db vs. heat flux � linear trend (slope influenced by cavity)
Use of LBM for boiling simulations KFKI
30 40 50 60 70 80 90
0.60
0.65
0.70
0.75
0.80
0.85
0.90
0.95
-model, homogeneous heating -model, inhomogeneous heating, q = 42900 W/m -model, inhomogeneous heating, q = 50050 W/m
Depa
rture
Diam
eter
[mm
]
Contact Angle [°]
0.4 0.6 0.8 1.0 1.2 1.4 1.60.4
0.5
0.6
0.7
0.8
0.9
1.0
-model, inhomogeneous heating -model, inhomogeneous heating -model, inhomogeneous heating -model, homogeneous heating a = 0.6307, b = -0.5109 a = 0.6275, b = -0.6423 a = 0.6750, b = -0.4899 a = 0.6620, b = -0.4888
Dep
artu
re D
iam
eter
[mm
]
g, gravitation (x 9.81 [m/s2])
Dd=a gb
NURISP SEMINARApril2-3, Karlsruhe
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30 40 50 60 70 80 90
0.60
0.65
0.70
0.75
0.80
0.85
0.90
0.95
-model, homogeneous heating -model, inhomogeneous heating, q = 42900 W/m -model, inhomogeneous heating, q = 50050 W/m
Depa
rture
Diam
eter
[mm
]
Contact Angle [°]
0.4 0.6 0.8 1.0 1.2 1.4 1.60.4
0.5
0.6
0.7
0.8
0.9
1.0
-model, inhomogeneous heating -model, inhomogeneous heating -model, inhomogeneous heating -model, homogeneous heating a = 0.6307, b = -0.5109 a = 0.6275, b = -0.6423 a = 0.6750, b = -0.4899 a = 0.6620, b = -0.4888
Dep
artu
re D
iam
eter
[mm
]
g, gravitation (x 9.81 [m/s2])
Dd=a gb
44000 46000 48000 50000 52000 54000 56000 58000
0.60
0.65
0.70
0.75
0.80
0.85
0.90
0.95
-model -model D
d = 9 10-6 +0.1716
Depa
rture
Dia
met
er [m
m]
Heat Flux [W/m]
30 40 50 60 70 80 90
1.2
1.4
1.6
1.8
2.0
2.2
2.4
2.6
-model, q = 42900 W/m-model, q = 50050 W/m-model
Rel
ease
Per
iod
[ms]
Contact Angle [°]
�f vs. θ� with flat surface the release period decreases sharply with increasing θ until it reaches minimum. With cavity the release period is a monotone increasing function of the θ and this function can be described well by a parabola.
Use of LBM for boiling simulations
KFKI
NURISP SEMINARApril2-3, Karlsruhe
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30 40 50 60 70 80 90
1.2
1.4
1.6
1.8
2.0
2.2
2.4
2.6
-model, q = 42900 W/m-model, q = 50050 W/m-model
Rel
ease
Per
iod
[ms]
Contact Angle [°]
� Increasing φ, Tw does not change at beginning then starts increasing (increase described by a cubic function of φ in line with data). φ where Tw starts to increase depends on modeling conduction or cavities.
� Modeling conduction, Tw starts increasing at higher φ for flat surface and even higher with cavities. Increasing φ, the Tw fluctuations increase, too.
5000 10000 15000 20000 25000 30000 35000 40000 45000300
350
400
450
500
550-model-model-model
Sur
face
Tem
pera
ture
[°C
]
Heat Flux [W/m]
Use of LBM for boiling simulations
KFKI
NURISP SEMINARApril2-3, Karlsruhe
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5000 10000 15000 20000 25000 30000 35000 40000 45000300
350
400
450
500
550-model-model-model
Sur
face
Tem
pera
ture
[°C
]
Heat Flux [W/m]
� Cavities can interact with each other, resulting in cancellation or freezing of bubble production in a neighbouring cavity (energy partitioning between cavities)
Is the wall boiling model able to detect the CHF value?
• Following the analysis of Kurul (1990), the heat flux at the wall is splitinto three terms:
• convective heat flux to liquid qc at the fraction of the wall area unaffected by the presence of bubbles,
• a quenching heat flux qq where bubbles departure bring cold water in contact with the wall periodically,
EDF
NURISP Mid-term Review Meeting, October 7 th, 2010 - BRUSSELS:Progress of SP2 activity at Mid-term
21
• a vaporisation heat flux qe needed to generate the vapour phase.
Convective heat flux
vaporisation
quench
the wall surface fraction A occupied by bubble nucleation reaches 1 in 8 CHF tests
DEBORA cases under CHF conditions-
• Values of A under critical heat flux conditions are between 10%and 70%.
• A was calculated as a function of the heat flux : A tends to 1 insome cases at CHF value but not in all cases.
• Various authors (Zuber) postulate that CHF occurs when theHelmholtz instability appears in the interface of the large vaporcolumns leaving the heating surface � bubble diameter atdetachment when the CHF is reached. In some cases, the Unal
EDF
NURISP Mid-term Review Meeting, October 7 th, 2010 - BRUSSELS:Progress of SP2 activity at Mid-term
22
detachment when the CHF is reached. In some cases, the Unaldiameter and the Rayleigh-Taylor diameter tend towards thesame value when the heat flux tends towards the CHF value. Butthe accuracy levels should be improved to prove the efficiency ofthe criterion.
� The wall model for nucleate boiling is not able to detect the CHFvalue.
Uncertainty of Modeling: Bubble Dep. Diameter
( )6
1
3
3
coscos32
sin864
−+⋅⋅
⋅−=
φφφ
ρρσ
gD
vlbubble
( ) 2n
1ii
i
ibubble(bubb) x
x
xDD ∑
=
⋅
∂∂= δδ
0.1
1
U_Dbubb [m]
d(Dbubb)/d(fi)*U(fi)
d(Dbubb)/d(sigma)*U(sigma)
d(Dbubb)/d(Drho)*U(Drho)
JSI
NURISP Mid-term Review Meeting, October 7 th, 2010 - BRUSSELS:Progress of SP2 activity at Mid-term
23
=D
dBarcsinφ
( ) ( ) gD
vl ⋅−⋅
−+⋅=
ρρσ
φφφ
3coscos32
sin24
Calculated uncertainty values forbubble departure diameter Dbubble
0.0001
0.001
0.01
0 20 40 60 80 100 120 140 160 180fi [°]
U_D
bubb
[m]
d(Dbubb)/d(Drho)*U(Drho)
Characteristic diameters are deducedfrom the equilibrium of the surfacetension and the buoyancy forces.
Uncertainty of Modeling: Bubble dep. diameter
10
12
14
16
18
20
D, D
bubb
[mm
]
D [mm]
Dbubb
Dfritz [mm]
10
100
1000
Ur_
D, U
r_D
bubb
[%]
Consideration of uncertainties of measured parameters may lead to significant deviation in prediction of D and Dbubb even for a simple equilibrium of buoyancy and surface tension.
JSI
NURISP Mid-term Review Meeting, October 7 th, 2010 - BRUSSELS:Progress of SP2 activity at Mid-term
24
Calculated diameters with error bars for virtual growing bubble D and departing bubble Dbubb vs. Fritz correlation (DFritz).
0
2
4
6
8
0 20 40 60 80 100 120 140 160 180fi [°]
D, D
bubb
[mm
]
0.1
1
10
0 20 40 60 80 100 120 140 160 180fi [°]
Ur_
D, U
r_D
bubb
[%]
Ur_Dbubb [%]
Ur_D [%]
( )vlFritz g
Dρρ
σφ−⋅
⋅⋅= 0208.0
Relative uncertainty for D and Dbubb
strongly depends on the wetting angle.
Wall-to-fluid heat transfer in boiling model
• “Two-phase” shear velocity affects the heat partitioning in boiling model
1. Modified single-phase heat transfer coefficient hlog
2
)ln(1
++ By
κ ( )TThA −=Φ
JSI
NURISP Mid-term Review Meeting, October 7 th, 2010 - BRUSSELS:Progress of SP2 activity at Mid-term
25
2. Characteristic velocity, appears in Unal’s model for dbw
,)ln(
1wuuByu
∆−+= ++δδ κ
250=+δy
log2log,
)ln(1
)ln(
∆−+
+=
++ uBy
Byhh ph
κ
κ ( )δTThA wphCphC −=Φ 2log,2,1
0
20000
40000
60000
80000
100000
0 1 2 3 4
Sin
gle
-phase
heat f
lux
(W/m
2)
z (m)
Wall func
Temp wall func
Wall-to-fluid heat transfer in boiling model: Results – ASU case
0
0.1
0.2
0.3
0.4
0.5
0 0.2 0.4 0.6 0.8 1
Vo
id fr
actio
n
(r-Ri)/(Ro-Ri)
Exp_tp6
base
Wall func
Temp wall func
1 70000
0.E+00
1.E-04
2.E-04
3.E-04
4.E-04
5.E-04
6.E-04
7.E-04
0 1 2 3
dbw
(m
)
z (m)
dbw_wf1
dbw_tp1
370
JSI
NURISP Mid-term Review Meeting, October 7 th, 2010 - BRUSSELS:Progress of SP2 activity at Mid-term
26
Negligible effect on evaporation, some influence only in PDB region.
0
0.2
0.4
0.6
0.8
1
0 0.2 0.4 0.6 0.8 1
Liq
. Vel
oci
ty (
m/s
)
(r-Ri)/(Ro-Ri)
Exp_tp6
base
Wall func
Temp wall func
Does not affect radialprofiles at measuringplane
0
10000
20000
30000
40000
50000
60000
70000
0 1 2 3
Evap
ora
tio
n h
eat f
lux
(W/m
2)
z (m)
Wall func
Temp wall func
350
352
354
356
358
360
362
364
366
368
0 1 2 3
TW
(K)
z (m)
Tw_wf1
Tw_tp1
Minor effect on dbw and Tw due to changed uδ
Texas A&M experiment
(Estrada-Perez and Hassan, IJMF 2010)
� Rectangular vertical channel W/H~1 approximates BWR flow channel
� PTV technique: velocity fluctuations and average velocities measured,
� Fluid HFE-301 at ambient pressure.
m. p.
475 mm
TAMU, JSI
NURISP SEMINARApril2-3, Karlsruhe
27
� Heated surface: 7mm wide, 175mm high,
� 455 mm from the channel inlet,
� fully developed region,
� Re [3309, 16549];
qw [0, 64 kWm-2].
0.120
1]
Re3309_q640_u'
Texas A&M: HFE 301 & Turbulence data
800
900
1000
HFE 301 Water
HFE 301 vs. water• Density ratios at given p/pc are preserved.• Experiment: pw/pHFE … 9.36 bar / 1 bar• BWR: pw/pHFE … 70 bar / 8 bar• PWR: pw/pHFE … 140 bar / 16 bar
Experimental turbulence� Fluctuations over the channel depth (w’)
were not measured, they are assumed to have the same values as v’
� kexp was defined from measured velocity fluctuations in one plane (u’, v’)
( )22exp '2'
2
1vuk ⋅+⋅=
TAMU, JSI
NURISP SEMINARApril2-3, Karlsruhe
28
0.000
0.020
0.040
0.060
0.080
0.100
0.000 0.002 0.004 0.006 0.008
velo
city
flu
ctu
atio
n [m
s-1
]
width [m]
Re3309_q640_u'
Re3309_q640_v'
u’
v’
w’0
100
200
300
400
500
600
700
800
0 0.02 0.04 0.06 0.08 0.1
p/pc
ρρ ρρ L/ ρρ ρρ
v
P=1 bar
Tsat= 37 C
p=9.36 bar
Tsat = 177 C
Texas A&M: 2D vs 3D mesh
0,2
0,3
0,4
0,5
0,6
axia
l vel
ocity
[m s
-1] .
3Dfine
2Dfine
TAMU, JSI
NURISP SEMINARApril2-3, Karlsruhe
29
0
0,1
0 0,002 0,004 0,006 0,008width [m]
2Dfine
� Due to the small W/H of the channel the geometry cannot be reduced to a 2D case.
� A full 3D domain with medium grid refinement 20x20x370 was used
Texas A&M: Results –Velocity profiles (Re= 9926)
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0 0.002 0.004 0.006 0.008
Liqu
id V
eloc
ity [m
s-1
]
width [m]
LiqVel (CFX)
LiqVel (NEPTUNE)
LiqVel (Exp)
Re= 9926
qw= 3.9 kWm-2
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0 0.002 0.004 0.006 0.008
Liqu
id V
eloc
ity [m
s-1
]
width [m]
LiqVel (CFX)
LiqVel (NEPTUNE V7)
LiqVel (Exp)
Re= 9926
qw= 42.3 kWm-2
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0 0.002 0.004 0.006 0.008
Liqu
id V
eloc
ity [m
s-1
]
width [m]
LiqVel (CFX)
LiqVel (NEPTUNE)
LiqVel (Exp)
Re= 9926
qw= 64 kWm-2
Liquid velocity TAMU, JSI
NURISP SEMINARApril2-3, Karlsruhe
30
width [m] width [m]
Turbulent kinetic energy
0.000
0.002
0.004
0.006
0.008
0 0.002 0.004 0.006 0.008
k l[J
kg-1
]
width [m]
k_eff (CFX)
k_eff (NEPTUNE)
k_eff (Exp)
Re= 9926
qw= 3.9 kWm-2
0.000
0.002
0.004
0.006
0.008
0 0.002 0.004 0.006 0.008
k l[J
kg-1
]
width [m]
k_eff (CFX)
k_eff (NEPTUNE)
k_eff (Exp)
Re= 9926
qw= 42.3 kWm-2
0.000
0.002
0.004
0.006
0.008
0.010
0.012
0 0.002 0.004 0.006 0.008
k l[J
kg-1
]
width [m]
k_eff (CFX)
k_eff (NEPTUNE)
k_eff (Exp)
Re= 9926
qw= 64 kWm-2
CHAPTAL Experimental Program :
Adiabatic two-phase flows (water-R116 gas)
• The CHAPTAL test section is a 5 m long vertical pipe with an inside diameter of 38 mm.
• Local measurements are performed at : 7.5D, 54.5D and 155.5D, where D = 38mm
qq qq
outlet
EDF
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38mm
• Strategy for validating separately the forces modelling and the bubble size modelling:
– Calculation with imposed bubble diameter
– Calculation with from the moment method
qqinlet
Liquid flowrate (kg/s) Gas flowrate (g/s) Case 1 1 14 Case 2 1 7 Case 3 1 20 Case 4 2 14
CHAPTAL calculations by NEPTUNE_CFD
EDF
NURISP SEMINARApril2-3, Karlsruhe
32
First set of computations on 3 meshing :1. a coarse grid (10 cells in the radial direction and 100 cells in the axial direction) , 2. a medium grid (20 cells in the radial direction and 200 cells in the axial direction)3. a fine grid (30 cells in the radial direction and 400 cells in the axial direction).
Results are similar
focus on forces modelling, not on the bubble diameter D*except for simulations called “polydispersion”, the experimental D* is imposed in the whole computational domain.
Case 1
Case 2
CHAPTAL calculations by NEPTUNE_CFD
EDF
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33
Unfortunately, surface tension for bubbles of Freon 116 immerged in liquid water is still unknown.several values between 0.01 and 0.07 N/m were tested. However, it is planned to measure σ in a near future.
Case 2
Case 3
Case 4
CHAPTAL calculations by NEPTUNE_CFD
EDF
NURISP SEMINARApril2-3, Karlsruhe
34
Case 4
• Unfortunately, we currently ignore the value of the surface tension forbubbles of Freon 116 immerged in liquid water, but the air-water surfacetension gives a satisfactory explanation of the concordance betweencalculations and experimental values
• Under this assumption, the maximum horizontal dimension of thedeformed bubble calculated using an empirical correlation given byWellek et al. (1966), is underestimated. Thus, considering the current setof models and available measurements, the tests featuring small bubbles
CHAPTAL calculations by NEPTUNE_CFD
EDF
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35
of models and available measurements, the tests featuring small bubblesshould be privileged in order to minimize the error on the Wellek’scorrelation.
Extension of the MUSIG approach to bubbly flow with condensation
Coalescence & break up not taken into account
•The best agreement was obtained with Hughmark model
0.30
0.40
mm
]
K16.118_6F: 0.608 m
ExpCFX
0.10
0.15
ctio
n [-]
F: 0.608 mExperimentCFX (total)dB<4.5 mm
0 10 20 30DB [mm]
0.00
0.10
0.20
0.30
0.40
H [%
/mm
]
K16.118_6I: 1.552 m
ExpCFX
0.000 0.020 0.040 0.060 0.080 0.100Radius [m]
0.00
0.03
0.05
0.08
0.10
Gas
vol
um
e fr
actio
n [-]
I: 1.552 mExperimentCFX (total)dB<4.5 mmdB>4.5 mm
HZDR
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with Hughmark model•Ranz and Marshall model undererestimated the heat transfer•Tomiyama model overerestimate the heat transfer
0 10 20 30DB [mm]
0.00
0.10
0.20
0.30
0.40
H [%
/mm
]
K16_118.6A: 0.221 m
ExpCFX
0.000 0.020 0.040 0.060 0.080 0.100Radius [m]
0.00
0.03
0.05
0.08
0.10
Gas
vol
um
e fr
actio
n [-]
A: 0.221 mExperimentCFX (total)dB<4.5 mmdB>4.5 mm
0 10 20 30DB [mm]
0.00
0.10
0.20
H [%
/m
0.000 0.020 0.040 0.060 0.080 0.100Radius [m]
0.00
0.05
Gas
vol
um
e fr
ac dB>4.5 mm
Extension of the MUSIG approach to bubbly flow with condensation
0 10 20 30 40 50DB [mm]
0.00
0.10
0.20
0.30
0.40
H [%
/mm
]
K16.118_6.0K: 2.538 m
ExpCFX
0.000 0.020 0.040 0.060 0.080 0.100Radius [m]
0.00
0.05
0.10
0.15
0.20
0.25
Gas
vo
lum
e fr
actio
n [-
]
K: 2.538 mExperimentCFX (total)dB<4.5 mmdB>4.5 mm
0.30
0.40
m]
K16.118_6H: 1.495 m
ExpCFX
0.15
0.20
0.25
ract
ion
[-]
H: 1.495 mExperimentCFX (total)dB<4.5 mmdB>4.5 mm
In a test with larger bubbles small deviations of the cross sectional averaged void fraction from the experiments can be explained by the
HZDR
NURISP SEMINARApril2-3, Karlsruhe
370 10 20 30 40 50
DB [mm]
0.00
0.10
0.20
0.30
0.40
H [%
/mm
]
K16_118.6B: 0.278 m
ExpCFX
0.000 0.020 0.040 0.060 0.080 0.100Radius [m]
0.00
0.05
0.10
0.15
0.20
0.25
Gas
vol
um
e fr
actio
n [-
]
B: 0.278 mExperimentCFX (total)dB<4.5 mmdB>4.5 mm
0 10 20 30 40 50DB [mm]
0.00
0.10
0.20
H [%
/mm
0.000 0.020 0.040 0.060 0.080 0.100Radius [m]
0.00
0.05
0.10
0.15
Ga
s vo
lum
e fr dB>4.5 mmexperiments can be explained by the
bubble sizes calculated too large. Here the neglected bubble fragmentation seems to play a role.
Polydispersion modelling with MUSIG
0.0000
0.0005
0.0010
d B [m
]
Expmonodispersed approachMUSIG
HZDR
DEBORA tests: Radial bubble size profile
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• Coupling wall boiling with population balance model: Better description of bubble size profile (interfacial area)
• blue line: bubble size dependent on liquid temperature• red line: (MUSIG) the increase of bubble size by bubble coalescence with
increasing distance from the wall can be described• P=2.62 MPa, G=2.103 kg m-2 s-1, Tin = 68.5 °C
0 0.002 0.004 0.006 0.008 0.01r [m]
0.0000
0.4
0.6
0.8
1.0
[-]
TSUB [K]13.8918.4322.526.9429.58
0.4
0.6
0.8
1.0[-
]
TSUB [K]13.8918.4322.526.9429.58
measurement calculation
Polydispersion modelling with MUSIG
volu
me
frac
tion
HZDR
DEBORA tests: Radial void fraction profile
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0 0.002 0.004 0.006 0.008 0.01R [m]
0.0
0.2
0 0.002 0.004 0.006 0.008 0.01R [m]
0.0
0.2
• P=1.4MPa, G=2.103 kg m-2 s-1
• test series with decreasing subcooling at the inlet� With decreasing subcooling in the radial volume fraction distribution shift from
wall to core peak – can be described by inhomogeneous MUSIG model
volu
me
frac
tion
Polydispersion modelling with MUSIG
bubble size distribution
at different positions x and RP1P2P3
Gas2 Gas1
Gas2Gas1
200
300
400
B [m
m-1]
x=3.5 mP : r=0.0095 m
HZDRCoupling wall boiling model with population balance model
NURISP SEMINARApril2-3, Karlsruhe
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• P=1.4 Mpa, subcooling at the inlet TSUB = 14 K• two dispersed phases � description of flow with core
peak
0.00 0.75 1.50 2.25 3.00dB [mm]
0
100
200
dαG/d
d B P1: r=0.0095 mP2: r=0.0045 mP3: r=0.001 m
Polydispersion effect in subcooled boiling
Typical DEBORA pdf
CEA
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Average bubble dBubble population in
saturated layer
Bubble population in subcooled core flow
after some condensation
Calculating condensation with a unique
diameter
Validation of NEPTUNE_CFD against PSBT by UPISA
Selected test:Sub-channel test section(PSBT test facility)
UPISA
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Selected test:
Subcooled boiling in PWR-type heated channels
(PSBT test facility)
Validation of NEPTUNE_CFD against PSBT by UPISA
Computational domain: 1/8 of cross section (by symmetry)
Meshes:10 000 ÷ 220 000 cells
UPISA
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Simulation set-up• Code: NEPTUNE_CFD V1.0.7
• Bubble diameter: uniform or aiequation (Wei Yao)
• Turbulence modelling– Liquid: κ−ε or Rij
– Vapour: Tchen or none
• Drag coefficient: incl. (edf) or Ishii
• Non drag coefficient� Lift, added mass (std. edf or Zuber), turb.
dispersion
• Heat transfer modelling� Liquid: bulk model (Astrid) or Grenoble model
� Vapor: Relax. time or Grenoble model
• Wall boiling: EDF or GRE model
Reference calculations results
“st edf_1249”
Case ααααEXP 0.22
st edf_1249 0.26(+ 18 %)
gre_1257 0.30(+ 36 %)
Validation of NEPTUNE_CFD against PSBT by UPISA
UPISA
NURISP SEMINARApril2-3, Karlsruhe
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“gre_1257”
• Reference results:– Overestimation of average void fraction in both cases– Fail to predict correct void distribution (too much vapour close to
wall, too little in the bulk)• Sensitivity analyses:
– Rij turbulence model (liq. phase): still overpredicts void fraction;
Validation of NEPTUNE_CFD against PSBT by UPISA
NURISP SEMINARApril2-3, Karlsruhe
45
– Rij turbulence model (liq. phase): still overpredicts void fraction; qualitative distribution closer to exp
– Bubble diameter (ai eq.) and lift coeff., for “st edf” case � failed due to convergence problems
– Bubble diameter (ai eq.) � failed due to convergence problems– Constant bubble diameter � no noticeable effect– 1.5% higher inlet velocity � void = 0.27 (overprediction reduced)– Grid refinement (axial) � no effect– Grid refinement (cross sectional) � slight increase in void
fraction � grid convergence not yet achieved• CFD is not yet more accurate than system code for average void
fraction prediction
DEBORA tests close to DNB
DEBORA tests with increasing Xth
A void peak appears close to the wall just before CHF
Is it a layer of detached bubbles?
NRI
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Is it a coalescence of attached bubbles?
NEPTUNE simulation
Simulation of tube and bundle CHF tests LWL
Example results: Case 4(vertically “shrunk” domain - 1:50)
Void fraction [ -]
centralrod
NRI
NURISP SEMINARApril2-3, Karlsruhe
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Void fraction [ -]
� Step 1: looking for a local DNB criterion using Tube data� Step 2: verify the criterion in actual rod bundle (LWL)
� αlim = 0.8 provides 10% accuracy in most cases in tubes� not good for low G & low P� grid spacer effects qualitatively predicted (higher mixing and higher CHF)
NRI simulations of CHF tests in tubes
Series 1: Variable X eq Series 2: Variable GNRI
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Series 3: Variable D Series 4: Variable p
DNB: Main achievements
� New data were used for modelling and validation:• TAMU rectangular boiling channel• KFKI data• DEBORA-TESS• CHAPTAL adiabatic bubbly flow• CHF in pipes• PSBT
� The main advances in understanding flow processes and in
NURISP SEMINARApril2-3, Karlsruhe
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� The main advances in understanding flow processes and in modelling are on the following:
– Wall function laws for momentum– Mechanical laws (interfacial forces and turbulence) consolidated
by CHAPTAL– Polydispersion effects in presence of boiling and condensation– CFD was validated in real rod bundle geometry (KFKI & PSBT)
DNB: CONCLUSIONS
� The state of the art in CHF prediction with two-phase CFD is the following:
– CHF in heated tube with steam-water is predicted with a 10% accuracy in the domain: 15< P <20MPa, -0.5 < X < 0.1, 1800 < G < 5000Kg/m2/s, 4 < D < 16mm
– CHF in rod bundle was predicted with a 20% accuracy and the effect of the spacer grids was qualitatively correct
– Larger errors were found for CHF in heated tube with Freon
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� Accuracy of CFD not yet sufficient for DNB prediction butalready useful for:� parametric studies for fuel design,� Improving subchannel models� more mechanistic CHF models
� Need of a DNB criterion: new experiments and DNS simulations