1. WATER AND LEAD-BISMUTH EXPERIMENTS: FLUENT AND STAR-CD SIMULATION
A. Peña, G.A. Esteban, A. Abánades
The University of the Basque Country,
Dpt. Nuclear Engineering & Fluid Mechanics. E.T.S.I. Bilbao, Spain

2. INDEX 1. INTRODUCTION 2. HYTAS EXPERIMENT 3. HEATED JET EXPERIMENT
4. KILOPIE EXPERIMENT
5. CONCLUSIONS

3. INDEX 1. INTRODUCTION 2. HYTAS EXPERIMENT 3. HEATED JET EXPERIMENT
4. KILOPIE EXPERIMENT
5. CONCLUSIONS

4. INTRODUCTION
The University of the Basque Country has been involved in different CFD code calculations, within the ASCHLIM project.
A group of CFD code oriented experiments have been designed with an important objective of the analysis focuses on describing the heat transfer viability of the particular window design prepared for MEGAPIE for a spallation target.
The experiments dealing with HLM, are being carried out in the THEADES loop in the KALLA facility of the IKET (Institute of Nuclear and Energy Technologies) in the FZK in Germany.
Other experiments have been carried out with water using almost the same 1:1 geometry constructed in plexiglass. This experiment is called HYTAS , and allows drawing relevant conclusions for the HLM case because the same Reynolds number is used apart from the same geometry scale.

5. INDEX 1. INTRODUCTION 2. HYTAS EXPERIMENT 3. HEATED JET EXPERIMENT
4. KILOPIE EXPERIMENT
5. CONCLUSIONS

6. coming down an annular gap, and going up through an inner cylinder
HYTAS EXPERIMENT
Experiment layout
A plexiglass module representing approximately a 1:1 scale of the MEGAPIE geometry.
The mean flow rate: 140 m3/h of water
coming down an annular gap, and going up through an inner cylinder
Two different geometries were used for the experiment considering the presence and absence of a by-pass, used to avoid stagnation points in the fluid close to the window that may entail hot spots when using HLM

7. HYTAS EXPERIMENT Simulation set-up CFD code: FLUENT
The meshing for the HYTAS experiment without the by-pass consists in mixed cells, generated by the GAMBIT code
For both calculations, the turbulence model is the RNG k-e with the standard wall functions, and the discretization scheme for the convective terms is the second order UPWIND
Geometry without by-pass

8. The geometry with by-pass: the number of cells is 165300.
HYTAS EXPERIMENT
Simulation set-up
CFD code: FLUENT
The geometry with by-pass: the number of cells is
If the by-pass is present, an additional flow of hot water equaling to 9.3 m3/h through the rectangular tube has been taken into consideration, the temperature of the secondary flux being 50 K hotter than the main flux through the annular gap.
Geometry with by-pass

9. Results and Discussion
HYTAS EXPERIMENT
Results and Discussion
Without by-pass
Flow recirculations
Stagnant points

10. HYTAS EXPERIMENT

11. Results and Discussion
HYTAS EXPERIMENT
Results and Discussion
With by-pass
There is flow recirculation inside the inner tube
No stagnant points but some flow can be seen entering the annular gap

12. Results and Discussion
HYTAS EXPERIMENT
Results and Discussion
With by-pass
The flow reaches a constant temperature in the inner tube, so the mixing is very good

13. INDEX 1. INTRODUCTION 2. HYTAS EXPERIMENT 3. HEATED JET EXPERIMENT
4. KILOPIE EXPERIMENT
5. CONCLUSIONS

14. With or without a slanted inlet to the inner tube
HEATED JET EXPERIMENT
Main flux
Experiment layout
Two different geometries
Bypass
With or without a slanted inlet to the inner tube
Fluid: Lead-Bismuth eutectic

15. Main Flux: Tª: 300 ºC and Q: 18 m3/h
HEATED JET EXPERIMENT
Simulation set-up
Main Flux: Tª: 300 ºC and Q: 18 m3/h
Flux through the by-pass: Tª: 350ºC and Q: 2 m3/h
The geometry used for the straight inlet is the same as the one used for the HYTAS experiment
The number of cells is for the geometry with the slanted inlet

16. CFD codes: FLUENT and STAR-CD (different users)
HEATED JET EXPERIMENT
Results and Discussion
Straight inlet
CFD codes: FLUENT and STAR-CD (different users)
FLUENT
STAR-CD

17. … but the mixture is quite good
HEATED JET EXPERIMENT
Results and Discussion
Straight inlet
In the plane perpendicular to the by-pass flux
Stagnant points
… but the mixture is quite good
recirculation

18. Temperature profiles are quite different
HEATED JET EXPERIMENT
Results and Discussion
Straight inlet
Temperature profiles are quite different
FLUENT
STAR-CD

19. Differences between 10 and 20 ºC
HEATED JET EXPERIMENT
Results and Discussion
Straight inlet
Temperatures in K
Differences between 10 and 20 ºC

20. Results and Discussion
HEATED JET EXPERIMENT
Results and Discussion
the change in the geometry configuration leads to different results
Straight geometry
Slanted geometry
Velocity vectors

21. Results and Discussion
HEATED JET EXPERIMENT
Results and Discussion
the change in the geometry configuration leads to different results
Straight geometry
Slanted geometry
Temperature contours

22. INDEX 1. INTRODUCTION 2. HYTAS EXPERIMENT 3. HEATED JET EXPERIMENT
4. KILOPIE EXPERIMENT
5. CONCLUSIONS

23. KILOPIE EXPERIMENT Experiment layout Simulation set-up
The bottom hemisphere is dismounted and it is substituted by a surface heating system, that will provide a heat flux of 140 W/cm2.
The flow rates through the annular gap and through the by-pass are the same as in the heated jet experiment, but the inlet temperature is 180 ºC for both fluxes.
Simulation set-up
The geometry used for this simulation is the one with the slanted inlet in the inner cylinder.
The boundary conditions, as well as the physical models, are the same as in the other experiment, except for the heat flux input. The inlet temperatures for the fluxes are 180 ºC, and there is a heat flux boundary condition in the wall of the hemisphere, with a value of 140 W/cm2.

24. KILOPIE EXPERIMENT
Results and Discussion
There are no stagnant points

25. Hemisphere projection
KILOPIE EXPERIMENT
Results and Discussion
Hemisphere projection
The maximum temperature is given at the window (595 K). It can be observed that there is almost an instantaneous cooling of the device, because not very far from the window the temperature is again the inlet one (453 K).

26. INDEX 1. INTRODUCTION 2. HYTAS EXPERIMENT 3. HEATED JET EXPERIMENT
4. KILOPIE EXPERIMENT
5. CONCLUSIONS

27. CONCLUSIONS
Some recirculation is foreseen in the experiments with liquid metals and water. STAR-CD temperatures are higher than the FLUENT. The discrepancy is thought to be due to the different near wall treatment employed by both codes for the thermal boundary layer behavior, and also the user influence could be important.
Although the coolability of the window seems to be guaranteed (no hot points are foreseen), the flow pattern is not properly driven into the inner tube.
Mass flow rates are higher in the heated jet experiment compared with the HYTAS experiment with water. This can contribute to the better flow patterns obtained. Fewer critical points appear in the heated jet experiment calculations, so it is a good result in order to continue with the experimental set-up.