Effect of particle angularity on flow regime transitions and segregation of bidisperse blends in a rotating drum

Granular segregation is a phenomenon that occurs when mixing different-sized particles. This work aims at comparing the segregation pattern and intensity in a bidisperse blend of spherical, cubic and icosahedral particles with a size ratio of 1.5 in a rotating drum. A model based on the discrete element method is used to simulate the flow of particles at rotational speeds ranging from 15 RPM to 115 RPM. This model is validated for monodisperse cubic particles. Segregation is shown to decrease with increasing particle shape angularity for a given rotational speed as long as the flow remains in the same regime. For all three shapes, the same sequence of segregation pattern occurs as the rotational speed increases (from a classic core segregation to a mixed state, and then to inverse segregation), but the speed thresholds for the transitions are shape-dependent and linked to the total kinetic energy of particles, as evidenced by a proposed apparent Froude number. The slip at the wall and the ability to spin explain why rounder shapes are less efficient to transfer kinetic energy from the wall into translational motion of the particles. This triggers regime transitions at higher rotational speeds for rounder particles, but at the same apparent Froude numbers. The transitions between cascading and cataracting, and between cataracting and centrifuging, occur at Fr-app approximate to 0.20 and 0.35, respectively, regardless of the particle shape.

Automated summary

The study shows that segregation decreases with increasing particle shape angularity at the same rotational speed. Different-shaped particles exhibit the same sequence of segregation patterns as rotational speed increases, but the transition speed thresholds are shape-dependent.