Study of atypical particle flow and free surface evolution behaviour in stirred tanks

Abstract

Stirred tanks are ideal vessels for material mixing reactions in the chemical sector. However, insufficient data on the complex contact collisions occurring inside these vessels hinder their appropriate design and utilization. This study employs a coupled discrete element method and volume of fluid method (DEM-VOF) to examine the evolutionary behaviour of atypical particle flow and free surface in stirred tanks. DEM is utilized to trace particle motion and interactions, while VOF is used to capture the phase interface between the gas and liquid phases. Simulations are conducted on three commonly used particle shapes-oblate ellipsoid, sphere, and prolate ellipsoid-varying their aspect ratios under the same volume of particles. The key results of the suspension, distribution, multiphase flow, and free surface behaviours in the stirred tanks were analysed. The results show that the suspension and distribution of the three particle shapes are not substantially different, with suspension stability primarily influenced. Notably, the suspension of oblate ellipsoid particles exhibits conspicuous fluctuations. Additionally, the particle shape influences the magnitude of turbulent kinetic energy in the paddle area, with oblate particles exhibiting the largest values and prolate ellipsoids the smallest values. The findings provide guidelines for designing and operating stirred tanks under optimal conditions.