Computational prediction of the just-suspended speed, N_js, in stirred vessels using the lattice Boltzmann method (LBM) coupled with a novel mathematical approach

The determination of the minimum agitation speed, N_js, to achieve the just-suspended off-bottom solid suspension state in liquids in stirred vessels is an issue of significant importance in industrial processes. Here, N_js was computationally predicted for a stirred, fully baffled vessel provided with different axial or radial impellers using an LBM-based CFD model coupled with a novel method to extract N_js from the computational results. Accordingly, the number of solid particles in a very thin control volume near the bottom of the vessel were computationally predicted over a range of agitation speeds, N, to determine the mass fraction of suspended solids, X_m. A regression analysis based on the logistic equation was then applied to the X_m-N curves and a simple, derivative-based mathematical method was applied to predict N_js. The results obtained with this novel computational approach were found to be in good agreement with previous experimental data.