A CFD approach for predicting minimum impeller speed (N-js) to achieve complete off-bottom, solids. suspension in mechanically-agitated vessels is presented. The method is based on observing the :Simulated transient profiles of solids volume fraction-for the layer of cells adjacent to the vessel floor and has been shown to be reliable and robust. Predicted N-js values for typical impeller systems were compared with well-known empirical correlations and good agreement was obtained.