Flow and heat transfer characteristics in randomly packed beds with small D/d ratios

The packed beds with small tube-to-particle diameter (D/d) ratios are widely utilized in various industrial applications such as strong absorption, exothermic catalytic converters, and nuclear reactor coolers. However, due to the significant pore structure change, uneven flow and heat transfer become apparent. This study employs the DEM-CFD method to construct spherical disordered packed beds with 2 < D/d < 4. Packed beds' flow and heat transfer characteristics with different D/d ratios are analyzed comprehensively from both local and global perspectives. The results indicate that pore structure and temperature influence the flow field distribution in the packed bed. The peak temperature can be reduced, and the heat transfer effect can be improved by decreasing the D/d ratio or increasing the inlet velocity. Simultaneously, there is a decrease in the average velocity peak value and its fluctuation. Specifically, when D/d ratio is from 3.96 to 2.97, there is a 9% decrease in peak temperature and an approximately 11% decrease in maximum velocity. These findings contribute to deepening our understanding of the packed bed's flow phenomena and enhancing design optimization for small D/d < ratio packed beds in industrial settings.