CFD simulation of solids off-bottom suspension and cloud height

Solids suspension in stirred tanks is important, especially in the mineral processing industry, and it is one of the factors that influence the process economics. Computational fluid dynamics (CFD), laser Doppler velocimetry (LDV) and optical attenuation methods are employed to investigate the off-bottom solids suspension in a fully baffled tank with an elliptical bottom and agitated by a hydrofoil propeller Mixtec HA735. The CFD solid-liquid mixing simulations are initiated with particles settled at the bottom of the tank. The three-dimensional transient flow field obtained by the CFD simulation shows a good agreement with both optical and LDV measurements. The transient CFD simulation approach gives a better prediction of the solids suspension than the steady state one, and the agreement between the simulation and experimental results is better for smaller particles. Methods are developed that correlate the results of the CFD simulation with typical experimental measurements and theoretical calculations for investigating cloud height and off-bottom solids suspension. An empirical correlation for the cloud height is suggested on the basis of the mixing features identified by the CFD and experimental methods. (C) 2006 Elsevier B.V. All rights reserved.