Effect of particle shape on the discharge from a mono-layer hopper

In this work, we performed experiments with spheres, rice-shaped particles with different aspect ratios, and macaroni-shaped particles in a quasi-two-dimensional hopper, where the thickness was adjusted to the minor dimensions of the particles such that a mono-layered system is created. We quantitatively investigate the vertical velocity and solid fraction profiles at the orifice and determine how these are influenced by the slope of the hopper. Interestingly, where the hopper angle hardly influences the velocity profile for rice-shaped particles, the magnitude of the velocity profile increases for spherical particles and decreases for macaroni particles with the steepness of the hopper. The spheres have flat solid fraction profiles for all hopper angles, but a transition from flat to dome-shaped profiles is observed with decreasing hopper steepness for all non-spherical particles. The discharge rate determined by integrating the product of the velocity and solid fraction profiles has good agreement with the experimentally measured discharge rate for all particle shapes.