Experimental and CFD-DEM study on local packing distribution and thermofluidic analysis of binary packed bed

In recent years, binary-packed beds have drawn attention due to their higher packing density and greater heat extraction capacity than mono-sized packed beds. In the past, the research on binary-packed beds mainly focused on finding empirical correlations for hydraulic permeability and equivalent thermal conductivity. Studies on fluid flow and heat transfer characterisation of the packed bed filled with binary particles are relatively scarce. In this work, the fluid flow and heat transfer analysis of purge gas flowing through the binary packed bed (1 ≤ size ratio ≤ 7 and at a volume of large particles = 40 %) is investigated using non-destructive experimental and Computational fluid dynamics-Discrete element modelling (CFD-DEM) approaches. An empirical correlation is developed for the local packing distribution inside binary packed beds. Based on the CFD-DEM results, the Ergun equation is modified to present the analytical equation for calculating the pressure drop for binary-packed beds at lower and higher Reynolds numbers. Further, the effect of the different size ratios on the fluid flow and heat transfer behaviour of the purge gas for binary-packed beds is investigated. The local packing factor increases with increasing the size ratio since small particles occupy the void among the large particles. This effect also increases the region with zero or negative flow at a higher size ratio. It is found that the purge gas penetrates deeper with an increasing size ratio; therefore, the heat extraction behaviour and the Nusselt number increase with increasing size ratios.