We modify the model developed by Ocone et al. [AIChE J. 3(8) (1993)] to include gas phase turbulence and then we test its predictive capabilities in the down flow of air and sand particle suspensions. Subsequently the flow of a diverse solid, namely fluid catalytic cracking (FCC) catalyst, is studied; the computational results for FCC show poor agreement with the experiments obtained by Cheng et al. [Chem. Eng. Sci. 54 (1999) 2019] and Ball and Zhu [Powder Technol. 114 (2000) 96]. However, when a counter-diffusive solid concentration term [Trans. IChemE 78 (2000) 860] is considered in the solid stress tenser, very good agreement with experimental data is observed. Furthermore, the effect of gravity, fluid turbulence, pressure drop and drag force is explored. (C) 2003 Elsevier B.V. All rights reserved.