(30b) Mixing of Floating Solids in Stirred Tanks: Scale-up Study Using CFD Modeling

Dissolution of solid excipients in liquid medium is a commonly encountered process operation for liquid dosage preparation in the pharmaceutical industry. When the solid phase has a lower density (or lower bulk density) than the liquid medium, the overall dissolution time is governed by the dynamics of the drawdown of light solid particles from the free liquid surface (when surface addition is used) and the subsequent dissolution of the suspended solids.

This work will demonstrate the utility of CFD simulation for the scale up of solid-liquid mixing in stirred tanks for light solid particles. Discrete Phase Modeling (DPM) simulations were used in conjunction with lab scale experimental measurements to develop a semi-empirical correlation for the prediction of rate of drawdown of light solid particles from the free liquid surface. The rate was correlated to the average liquid velocity at the free liquid surface. Since, this correlation is based on a fundamental hydrodynamic parameter, velocity, rather than an operating parameter such as impeller speed, it can be used for a variety of impeller types and tank geometries. This work demonstrates this correlation for four different mixing tank designs/impeller types. Effect of scale of the equipment was established based on the DPM simulation results.