1. Multiphase Flow Heat Transfer in Fuel Assemblies
January 2014
ASCOMP; ASCOMP Inc. USA,

2. The Westinghouse 24-rod mock-up
The Westinghouse 24-rod mock-up of SVEA-96 fuel bundle
Caraghiaur & Anglart (NED, 2009)

3. The Westinghouse 24-rod mock-up
The Westinghouse 24-rod mock-up of SVEA-96 fuel bundle
KTH Stockholm (CFX, cells)

4. The Westinghouse 24-rod mock-up
ASCOMP (TransAT, IST MESH). From CAD (left) to OST grid (right). Note that the very coarse mesh shown in right is for illustration only.

5. The Westinghouse 24-rod mock-up
ASCOMP (TransAT, cells)

6. The Westinghouse 24-rod mock-up
KTH Stockholm (CFX)
ASCOMP (TransAT)

7. The OECD PSBT 5x5 Benchmark
The OECD PSBT 5x5 Benchmark with 3 spacers (3 million cells, K-e model)

8. The OECD PSBT 5x5 Benchmark

9. The OECD PSBT 5x5 Benchmark

10. The OECD PSBT 5x5 Benchmark
Flow field and heat contours downstream the 1st simple spacer

11. The OECD PSBT 5x5 Benchmark
Flow field and heat contours downstream the 1st mixing vane

12. The OECD PSBT 5x5 Benchmark

13. NUPEC PWR Test Facility

14. Problem Description (PSBT OECD)
P=13.0 mm
Flow outlet
Fuel Rod
r=5 mm
L=1000 mm
flow cross section
Heat flux q”
Fig. 1. Computational domain: Dimensions & BC’s.
Benchmark definition within CASL: Lakehal & Buongiorno, 2011:
main changes: length reduced to 1m from 3m, power to 1.6kW from 7 MW, and thus Re=GDe/  4.8105 to  1.0104

15. Saturation temperature Saturation temperature
Problem Description (PSBT OECD)
Pressure
15.5 MPa
Saturation temperature
344.6C
Inlet temperature
290C
Mass flux
3333 kg/m2s
Heat Flux
581 kW/m2
Power MW
Table 1: Reference operating Cdts. for PSBT OECD cases (Rubin et al., 2010).
Pressure
15.5 MPa
Saturation temperature
344.6C
Inlet temperature
290C
Mass flux
74.1 kg/m2s (or Re=300)
Heat Flux
50 kW/m2
Power
1.57 kW
Table 2: Downscaled operating flow Cdts. for LES

16. Flow along a heated single rod at Re*=300
Ret=300
Number of nodes
Resolution
Grid type
total number of cells
x-y z
Dx+--Dy+
N blocks
Grid Med
40-40
798
208
BFC
1,317,400
Grid Fine
60-60
1.600
832
6,011,200
Figure 3. Medium (left) and fine (right) grids for LES (x-y). Arrows show 00 and 450 segments
q=450
q=00
SGS model: LES (Dynamic SGS model)
Schemes: Central 2nd order; RK 3rd order in time
Adaptive time-stepping ~ Dt = s (CFL = )
Days on the DOE Jaguar on 144 and 832 MPI // cores

17. Results
Figure 4. Fine vs. medium resolutions (non-scaled domain): Instantaneous cross-sectional velocities and temperature contours.

18. Results Fine grid: instantaneous Fine grid: time average
Medium grid: instantaneous Medium grid: time average

19. Results Fine grid: instantaneous Fine grid: time average
Medium grid: instantaneous Medium grid: time average

20. Results (comparison with DNS of pipe flow)
Medium grid Fine grid
Figure 7a. Mean velocity profiles across the subchannel (00 & 450) compared to the DNS of Eggels (1994).
Medium grid: 0 and Fine grid: 0 & 450
Figure 7b. Time averaged normal-stresses profiles (<w’w’>)

21. Global Results =1.826p/D-1.043=1.33 Quantity Medium grid Fine grid
Analytical/Exp.
Pressure drop DP [Pa]
10.223
10.52
~ 10.0
Heat transfer coefficient (HTC) at XONB
[kW/m2K]
1.495
1.535
 1.62 (Colburn)
 2.16 (Col-W*)
 1.44 (Gnielinski)
 1.99 (Gnlsk-W)
 1.50 (Petukov)
 2.00 (Ptkov-W)
Distance to XONB [m]
Min-max
0.49–0.57
0.49–0.6
~ 0.59 (Colburn)
~ 0.79 (Col-W)
Thermal entry length [m]
0.21–0.28
0.21–0.29
~ 0.29–0.46
=1.826p/D-1.043=1.33
*W means with the Weisman (1959) correction factor

22. Convective boiling phenomenon: The physical reality of turbulent confined bubbly flow is way more complex than the idealized conditions considered in two-phase flow studies (smooth or sinusoidal wavy films, spherical or elliptic droplets and bubbles, etc.). Turbulence-bubbles interactions is mysterious!
Bubble layer in high-subcooling, high-mass-flux, high-pressure, flow boiling of Freon near the point of DNB. The situation is qualitatively similar to the PWR hot channel during a transient overpower event.

23. Bubbly-flow boiling: Debora test case (CEA)
Iso-contours of transport quantities, including liquid and vapour temperature. 2D Axisymmetric simulations TransAT.

24. Bubbly-flow boiling: Debora test case (CEA)
Test Case: DEBORA Experiments of Manon et al (2000, 2001)
Pipe Length: 5m
Pipe Diameter: 19.2 mm

25. Bubbly-flow boiling: Debora test case (CEA)
There are differences between the 2-fluid & the N-phase homogeneous models. Same grid, same turbulence model, same comp. parameters.
All models fail near the wall for Tin=73.7 C
Void Fraction for Case 2 & 3: Tin = 58.4 C and 63.4 C
Void Fraction for Case 4 & 5: Tin = 67.9 C and C
Void Fraction for Case 6 & 7: Tin = 72.6 C and 73.7 C

26. Bubbly-flow boiling: Lee et al. & Tu & Yeoh (KAERI)
Test Case: Experiments of Lee, Park & Lee (2002) and Tu & Yeoh (2003)
Pipe Length: 2.376m
q=152.3 kW/m2
Gl=474 kg/(m2s)
P=0.14 Mpa
ΔTsub=11.5 K. a
Norm. Radial distance
Heat flux
mass flux
Tinlet
Tsat
MW/ m2
kg/m2/s K
0.1523
474
371.5
383

27. Bubbly-flow boiling: Bartolomei Test Case
Test Case: Experiments of Bartolomei et al (1982)
Pipe Length: 1.4m
Heated Length = 1m
q =1.2 MW/m2
Gl= 1500 kg/(m2s)
P = 6.89 Mpa
ΔTsub= 63 K.

28. Heat transfer in tube buddle in a steam generator
3D Setup (SNERDI)
Cold water
P2=5.8MPa
Tf=259 ℃
va=0.63 m/s
Tsat = 271 ℃
Location and size of tube and supports
Geometry of the flow field
Cold water
Hot Water
P1=15.5MPa
Ti= 322℃
vi=5.3m/s
Hot water
Cold water
Conjugate heat transfer through the tube to heat the cold water where phase change occurs.
Cross-Sectional view of support *
* Coarse grid is shown to illustrate the cross-section

29. Heat transfer in tube buddle in a steam generator
3D Results (SNERDI)

30. NUPEC PWR Test Facility: Phase average
Testcase
Pressure
[MPa]
Inlet Temp
[°C]
Power
[kW]
Mass Flux
[kg m-2s-1]
1.2211 15
295.4 90 11
1.2223
319.6 70
1.2237
329.6 60
1.4411 10
238.9 5
1.4325
253.8 2
1.4326
268.8
Cell Size (in mm)
No. of Cells
No. of Processors
Wall Clock Time
(in days)
5.31
9216 1
0.33
2.655
73728 8
0.75
1.328
108
1.5
0.885
128 4

31. NUPEC PWR Test Facility: Phase average
a) ∆x = 2.65mm b) ∆x = 1.328mm ) ∆x = 0.885mm
Steady State void fraction profiles for different grids (Testcase: ).