Investigation of hydrodynamic and heat transfer performances in grille-sphere composite pebble beds with DEM-CFD-Taguchi method

In the present paper, grille-sphere composite pebble bed (GSCPB) is developed to improve the hydrodynamic and heat transfer performances for high temperature gas cooled reactor with 10 MW (HTR-10). The fluid flow and heat transfer characteristics in typical GSCPB channels are numerically investigated, and the effects of typical parameters on the pressure drop and maximum pebble temperature inside are carefully analyzed with Taguchi method. Firstly, in the GSCPB bed, the grille can not only support the pebbles to achieve a structured packing quickly, but can also enhance convective heat transfer from pebbles to the fluid. With proper design of grille inside, the heat transfer rate would be improved and the pressure drop would be reduced in GSCPB channel when compared with traditional random pebble bed. Secondly, the effect of sub-channel width to pebble diameter ratio (N) on both the hydrodynamic and heat transfer performances in GSCPB channel is quite significant. The contribution ratios of N on the pressure drop and maximum pebble temperature in GSCPB channel are of 86.3% and 81.0%, respectively. Finally, with Taguchi method, the optimum design parameter combinations are obtained for the lowest pressure drop and lowest maximum pebble temperature in GSCPB channels, respectively.