Discrete Element Method–Volume of Fluid Simulation of Drawdown and Dispersion for Floating Particles in Stirred Tanks: Influences of Impeller Parameters

Abstract

Exploring the drawdown and dispersion behaviors of particles in stirred tanks can provide insights and valuable references for optimizing the design of equipment and improving the efficiency of the stirring process. In this article, the kinetic behaviors of drawdown and dispersion of floating particles in the stirred tank were simulated by the DEM-VOF (discrete element method−volume of fluid) model. The influences of impeller parameters (blade number n, rotation speed w, eccentric distance l, and off-bottom clearance h) on the granular characteristics (particle distribution, coupling force, total force, and translational/rotational kinetic energies), fluid dynamics (fluid velocity and turbulent kinetic energy), and gas−liquid free surface were investigated. The results show that the drawdown process of floating particles can be divided into the pull-down stage, dispersion stage, and cycle stage. With the increase in n, w, l, or h, the duration of the pull-down stage decreases, while the duration of the cycle stage increases. Due to the vortex effect and turbulent motion in the stirred tank, both the particle characteristics and flow dynamics change with the impeller parameters. Besides, large n or w, small l, and moderate h result in the deeper gas−liquid free surface.