The model proposed by Karabelas has been modified for the prediction of solid concentration and particle size distributions for the flow of multi size particulate slurries through pipe, 2-D duct, and open channel. The experimental data reported in the literature have been used to establish the limitations of the Karabelas model. Based on extensive analysis of the experimental data, modifications have been proposed in the model to overcome the deficiencies. In particular, the effect of solid concentration on particle settling and turbulent diffusivity has been incorporated into the modified model. The modified model predicts the solid concentration and particle size distribution with reasonable accuracy for all the geometries considered.