(339j) Granular Flow and Segregation in a Bladed Mixer

Bladed mixers are commonly used in a variety of areas, ranging from the bulk chemical to the food and pharmaceutical industries. The appeal of these mixers comes from their ability to handle a wide variety of solids ranging from free flowing to cohesive powders and even pastes. These unit operations often involve the use of components with particle size distributions. Particle size differences have been shown to cause segregation in many granular systems, a phenomenon which could jeopardize product quality in industrial scenarios. Despite the common used of polydisperse materials, the effect of particle size distributions on the flow behavior observed in bladed mixers is not fully understood.

In this work, we study the effect of polydispersity on flow and segregation in bladed mixers via particle dynamic simulations. Segregation patterns and resulting velocity profiles are compared to those observed experimentally. In bladed mixers, a 3D recirculation zone develops in-front of the blades which enhances radial and vertical mixing. We find that the intensity of the recirculation zone increases when the number of particle sizes is increased. This suggests that convective mixing in the radial and vertical directions is enhanced with a higher amount of polydispersity. Additionally particle diffusivities increase when the number of particle sizes is increased. This suggests that polydispersity enhances diffusive mixing. The observed increase in convective and diffusive mixing leads to a lower degree of size segregation for the cases with more types of particle sizes.