CFD simulation of particle suspension height in stirred vessels

Computational fluid dynamics (CFD) simulation capabilities for stirred solid-liquid dense systems are explored. These systems may give rise to the formation of a thick and well defined clear liquid layer in the upper part of the vessel whose extension progressively reduces with increasing impeller speed. Experimental measurements of the suspension height (the height of the particle laden layer) were carried out at various agitation speeds for a variety of solid-liquid systems in a fully baffled transparent tank. A clear layer of liquid was actually observed in all runs, with the suspension height almost linearly dependent on agitation speed. CFD simulations of the above described systems were performed in order to test their ability to reproduce the formation of the clear liquid layer. To this end, a Eulerian-Eulerian multi fluid model (MFM) was adopted in conjunction with the sliding-grid (SG) algorithm, thus resulting in fully predictive simulations of the two-phase system. Computational results indicate that the formation of a clear liquid layer in the upper part of the vessel is actually predicted by the modelling techniques adopted. Also, its extension is almost quantitatively reproduced by the simulations.