CFD MODELLING OF PARTICLE SUSPENSION IN STIRRED TANKS

Mixing of solid particles into liquids in mechanically agitated vessels is a topic of primary importance for several industrial applications. A great deal of research efforts has been devoted so far to the assessment of the minimum impeller speed (Njs) able to guarantee that all particles are suspended. Conversely, only little attention has been paid to the evaluation of the amount of solid particles that are suspended at impeller speeds N lower than Njs, despite the fact that in a number of industrial applications agitation speeds smaller than Njs are actually adopted [1,2]. The present work deals with dense solid-liquid partial suspensions in baffled stirred tanks and particularly focuses on the prediction of the amount of suspended particles at a number of angular velocities by means of Computational Fluid Dynamics. An Eulerian-Eulerian Multi Fluid Model coupled with a standard k-epsilon turbulence model is adopted for CFD simulations. Both Sliding Grid and Multiple Reference Frame approaches are employed to simulate the impeller-tank relative rotation. The computational model is validated by comparison with purposely collected experimental data. 1.Oldshue, J. Y., (1983). Fluid Mixing Technology, Chapter 5, McGraw-Hill, New York, NY. 2.Rieger, F., Ditl, P., Havelkova, O., (1988). Suspension of solid particles–concentration profiles and particle layer on the vessel bottom. Proceedings of the 6th European Conference on Mixing, Pavia, Italy, 24-26 May, 251-258.