(77d) Segregating Rods and Spheres: Simulation and Modeling

Many studies of segregation of flowing granular materials focus on spherical particles, even though in practice particles can have non-spherical shapes. Here we focus on mixtures of rod-like (cylindrical) particles of the same diameter but different lengths and mixtures of rod-like and spherical particles by implementing particle shapes described by super-ellipsoids in DEM simulations. To validate the effectiveness of super-ellipsoids, we compare to previous "true geometry" models of cylindrical particles. Then we use super-ellipsoids to study particle size segregation in bounded heap flow for a variety of particle diameters and lengths, comparing results with supporting experiments. In the flowing layer of a bidisperse rod mixture in a bounded heap flow, shorter rods percolate toward the lower portion of the flowing layer while longer rods rise toward the upper portion of the flowing layer. The rods tend to deposit on the underlying bed of particles in the heap such that they are aligned with the flow with the smaller rods deposited upstream of the larger rods due to segregation. Likewise, spherical particles segregate from rods having the same diameter. The percolation velocities related to the segregation depend on the local shear rate and the concentration of the other particle species, just as is the case for size or density bidisperse spherical particles. Using this percolation velocity and an appropriate value for collisional diffusion, the advection-diffusion-segregation continuum model for segregation successfully predicts the segregation of rod-like particles of different lengths as well as rod-like and spherical particles.