CFD prediction of mean flow, power number, mixing time and just suspended speed in mixing tank

Efficient multiphase mixing in stirred tanks is essential for chemical, pharmaceutical, and food processes. This study examines the relationship between power number (NPo), just-suspended speed (Njs), and mixing time to improve energy efficiency and suspension performance. Computational fluid dynamics (CFD) simulations were performed in ANSYS Fluent for a fully baffled, flat-bottom tank fitted with a down-pumping six-bladed pitched-blade turbine. The Reynolds-Averaged Navier–Stokes (RANS) turbulence model, multiple reference frame (MRF) approach, and discrete phase model (DPM) were applied to characterize fluid flow and solid–liquid interactions. Predicted impeller power numbers and mixing times agreed with published experimental data, with an average deviation of about 6.0%. However, the prediction of Njs remained challenging, even when power draw, mixing time, and flow field were reproduced with reasonable accuracy. Therefore, caution is advised when predicting solid–liquid dispersion in stirred tanks.