The Effect of the Number of Impeller Blades on Granular Flow in a Bladed Mixer

Simulations of granular flow of monodisperse, cohesionless spherical glass beads in a cylindrical bladed mixer agitated by an impeller were performed using the discrete element method (DEM). The number of impeller blades was varied from 1 to 4 blades, and the impact of the number of blades on granular flow behaviors and mixing kinetics was investigated. It was found that particle velocities in an agitated mixer were influenced by the number of the blades used in the mixing system. Higher radial and vertical velocities of particles were observed in the 1- and 2-bladed mixers, which led to more pronounced three-dimensional recirculation patterns. However, the tangential velocity components of particles in the 3- and 4-bladed cases were larger. Additionally, it was found that using two or three impeller blades provided better mixing performance than using one blade or four blades, evaluated by calculation of the relative standard deviation (RSD) and the Lacey index values of the systems. Granular temperature and particle diffusivities obtained for the 2- and 3-bladed cases were also higher than those for the 1- and 4-bladed mixers. Solids fraction analysis showed that dilation of the particle bed occurred to the most extent in the 2-bladed mixer. Contact force network data showed that using different numbers of impeller blades led to significant differences in the force distribution. Finally, the effect of scaling up was evaluated by varying the mixer diameter to particle diameter ratio. Increasing the mixer diameter to particle diameter ratio was found to have little impact on flow and mixing behaviors.