Modifying the inter-phase drag via solid volume fraction gradient for CFD simulation of fast fluidized beds

The conventional drag model in two-fluid simulation, which assumes uniform particle distribution in a computational grid, overestimates the drag force, thus failed in capturing the subgrid-scale strands and resolvable-scale clusters. This work proposed a new modification to the conventional drag model through considering the heterogeneous distribution of solid volume fraction (SVF), especially, in the inter-phase boundary (i.e., cluster boundary). The resulting drag model is a function of particle Reynolds number, SVF and the gradient of SVF. This straightforward modification is consistent with the elaborately filtered-approach-based modification method in nature. A CFD simulation for a two-dimensional riser was conducted to validate the new drag model. The outlet solid mass flux, axial and radial time-averaged voidages from the new drag model agreed well with the experimental measurements, and these results were far better than those from the conventional homogeneous drag models. (c) 2017 American Institute of Chemical Engineers AIChE J, 63: 2588-2598, 2017