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

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

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

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.

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

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

HYTAS EXPERIMENT Simulation set-up CFD code: FLUENT The meshing for the HYTAS experiment without the by-pass consists in 223723 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

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 165300. 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

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

HYTAS EXPERIMENT

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

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

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

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

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 386783 for the geometry with the slanted inlet

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

… 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

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

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

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

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

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

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.

KILOPIE EXPERIMENT Results and Discussion There are no stagnant points

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).

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

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.