Discrete element method study of effects of the impeller configuration and operating conditions on particle mixing in a cylindrical mixer

Abstract

We employed the discrete element method to study the effects of the impeller configuration (i.e., blade diameter, inclination angle, and blade number), rotational speed, and fill level on the flow and mixing of particles in a cylindrical mixer equipped with flat and inclined blades. The coefficient of rolling friction, coefficient of static friction, and coefficient of restitution were experimentally determined before the simulation, and simulation results of the torque and surface particle distribution were validated in experiments, particularly when using a true Young’s modulus in the discrete element method. The performance of the mixer was assessed using the Lacey mixing index. The input work per unit volume was used to represent the mixing efficiency. The circumferential velocity and axial diffusion coefficient of the particles were quantitatively analyzed to reveal the effect of particle flow on the mixing. It was found that the mixing performance and efficiency of a three-blade mixer are better than those of two- and four-blade mixers. For pitched blades, a three-flat-blade mixer has better mixing performance than a three-45°-blade own-pumping or a three-45°-blade up-pumping mixer, but the mixing efficiency of the three-45°-blade up-pumping mixer is the best among these three mixers. As the rotational speed increases, the mixing performance improves but the mixing efficiency hardly changes. When the fill level is 0.4 times the cylinder diameter, the 160D two-flat-blade mixer has good mixing performance with high mixing efficiency. The circumferential velocity has the greatest effect on mixing performance for side-by-side initial loading.