A model for cluster size in risers

Particles in gas-solid flows aggregate to move as "clusters" and simultaneously develop gas "voids" free of particles. A model for gas-solid flow in risers considering the presence of clusters and voids is presented. Equations are developed to estimate the size of clusters considering "ratio of cluster volume to void volume to be equal to the ratio of cluster volumetric fraction to void volumetric fraction in the bed". Estimates of cluster size compare well with the experimental observations reported in the literature. Equations developed for slip ratios and gas to particle effective drag coefficients are inline with the trends reported in the literature. (c) 2009 Elsevier B.V. All rights reserved.