Microscale drag model considering the effect of interface between dense and dilute phases for gas–solid suspensions at moderate Reynolds numbers

Abstract

Particle-resolved direct numerical simulations of flows past various fixed structures of spheres are performed to study the drag force at local Reynolds numbers up to 250. At the gas–solid interface, the drag force is found to be 5%∼800% of that estimated by BVK law (Beetstra et al. AIChE Journal, 2007, 53(2):489-501) at different particle Reynolds numbers and solid volume fraction gradients. Thus a microscale drag model at the cluster interface is developed as a function of the particle Reynolds number and the solid concentrations of dense and dilute phases. Assessments of the proposed drag model are performed with direct numerical simulations of flows past plug-like, spherical, ellipsoidal clusters as well as bubble-containing structures. The results show that the new model well captures the drag variations at microscales of several sphere diameters and correlates well with the solid concentrations and velocities of dense and dilute phases.