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

¹ Faculty of Chemical and Process Engineering Technology, Universiti Malaysia Pahang Al-Sultan Abdullah, Gambang 26300, Pahang, Malaysia
² Centre for Research in Advanced Fluid and Processes (Fluid Centre), Universiti Malaysia Pahang Al-Sultan Abdullah, Gambang 26300, Pahang, Malaysia
³ Department of Biotechnology, Faculty of Science & Humanities, SRM Institute of Science and Technology, Ramapuram, Chennai 600089, Tamil Nadu, India
⁴ Department of Biotechnology, Saveetha School of Engineering, Saveetha Institute of Medical and Technical Sciences, Chennai 602105, Tamil Nadu, India

^* Corresponding author: jolius@umpsa.edu.my

Abstract

Efficient multiphase mixing in stirred tanks is essential for chemical, pharmaceutical, and food processes. This study examines the relationship between power number (N_Po), just-suspended speed (N_js), 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.