Granular segregation in discharging cylindrical hoppers: A discrete element and experimental study

The segregation of granular materials due to differences in particle properties occurs during a variety of handling and transport processes, such as flow from a hopper. In the present work, the discrete element method (DEM) is used to investigate segregation of granular materials during discharge from a hopper. The effects of various particle properties and hopper geometries on the segregation of a spherical, bidisperse granular material during hopper discharge are studied. Particle contacts are modeled using a soft-particle model consisting of a hysteretic spring system and sliding friction. The effects of the particle diameter ratio, density ratio, fines mass fraction, hopper wall angle, hopper cross-sectional shape, and the initial fill conditions are investigated.These computational results are compared to those from a small experimental system with the same hopper dimensions and particle properties. The use of this small-scale system permits a novel, one-to-one comparison with the DEM model predictions for the purpose of model validation. The experiments utilize bidisperse glass spheres in a small, Plexiglas cylindrical hopper that is used in the ASTM International standard test for sifting segregation. Particles are discharged from either a ‘mass-flow’ or ‘funnel-flow’ hopper design and collected transiently in equal volumes until the hopper is empty. Analysis of the weight fractions of fine and coarse particles is conducted by sieving. A comparison of the computational and experimental results provides an indication of the model's success at predicting segregation during hopper discharge and the applicability of the DEM model to other granular flow systems.