Study of Solid-Liquid Mixing in Agitated Tanks through Computational Fluid Dynamics Modeling

Solid liquid mixing is one of the most important mixing operations due to its vast applications in many unit operations such as crystallization, adsorption, solid-catalyzed reaction, suspension polymerization, and activated sludge processes. In this study, a computational fluid dynamics (CFD) model was developed for solid liquid mixing in a cylindrical tank equipped with a top-entering impeller to investigate the effect of impeller type (Lightnin A100, A200, and A310), impeller off-bottom clearance (T/6-T12, where T is tank diameter), impeller speed (150-800 rpm), particle size (100-900 mu m), and particle specific gravity (1.4-6) on the mixing quality. An Eulerian Eulerian (EE) approach, standard k-epsilon model, and multiple reference frames (MRF) techniques were employed to simulate the two-phase flow, turbulent flow, and impeller rotation, respectively. The impeller torque, cloud height, and just suspended impeller speed (N-Js) computed by the CFD model agreed well with the experimental data. The validated CFD model was then employed to calculate the solid concentration profiles by which the degree of homogeneity was quantified as a function of operating conditions and design parameters.