Pore-scale simulation on flow and heat transfer characteristics in packed beds with internal heat sources at low Reynolds numbers

Abstract

Packed beds with internal heat sources are widely used in various engineering applications. But the effects of the internal heat source on the flow and heat transfer in the packed beds received less attention. In this study, the flow and heat transfer characteristics in packed beds with internal heat sources were studied at low Reynolds numbers to assist the design of the solid breeding blanket in the fusion reactors. Through the pore-scale simulations, the local behaviors (including flow velocity, temperature and fluid properties) and macroscopic flow and heat transfer characteristics were analyzed. It was found that with the internal heat sources, the fluid properties vary significantly form the packing inlet to outlet (e.g. the density decreases by 34% and the viscosity increases by 31% in the most). Due to the variations of the fluid density and viscosity, the conventional Ergun and Blake-Kozeny-Macdonald equation do not predict the pressure drop in the packed bed well. Then a modified model by introducing a modified coefficient considering the variable properties is proposed to predict the pressure drop of the packed bed with internal heat sources. The average deviation between the modified pressure drop model and the pore-scale simulation results is only 1.5%. Then a modified heat transfer model was proposed to predict the heat transfer characteristics of the packed bed with internal heat sources at low Reynolds number flow (Re <1.8). The deviations of the predictions by the modified model are within ±30% from the simulation values.