Discrete element investigation of flow patterns and segregation in a spheronizer

Powder flow in a spheronizer is characterized by a toroidal motion and the flow patterns depend on the disc velocity and the fill level, but also on the particle properties. This work investigates numerically, with a discrete element method (DEM), the impact of these parameters on segregation patterns and the flow dynamics for bidisperse particle size distributions. Characterization of the segregation, by means of a mixing index and the relation with the shear stress in the toroidal domain, is presented. Characteristics, such as mixing curves, concentration profiles and azimuthal velocity correlations, are discussed. A logarithmic expression has been developed to account for the shear stress on the evolution of the azimuthal velocity inside the particulate bed. The combination of the mixing indexes and the concentration profiles is used to quantify the changes observed on the segregation when the fill level and the rotational rate of the spheronizer disk are varied.

► Model predictions of the velocity profile are improved by including the shear rate.
► There exists an optimal rotational rate that maximizes the state of mixedness.
► The segregation occurs in the zones characterized by low shear rate values.
► Mixing indices allows to evaluate the relative importance of the segregated zones.