Discharge of spheres and dumbbells mixed with fine grains from a 3D silo

The flow of mixtures of non-spherical particles from silos is extensively observed in various industries. In this paper, we study the flow of binary mixtures of large grains mixed with fine spherical particles during the discharge of a silo with a circular orifice in its base. In particular, we focus on the effect of the shape of the large grains by using either spheres or dumbbell-shaped grains (mung beans). The flow rate is measured for various diameters of the orifice (D) and mix ratio of small and large particles (χ). The pure systems (no added fine grains) show equivalent flow rates for spheres and dumbbells. When fine grains are added to a sample of large particles, the effective flow rate of the big grains (diameter db) can increase. We observed that this is the case for both spheres and dumbbells. We propose a scaling of the flow rate, for binary mixtures, that allows us to assess the effect of the particle shape by removing the particle size contribution. The results suggest that for D/db ≲ 6.0 the shape of the large particles does not affect its flow rate for these low aspect ratio dumbbell shapes. However, for larger orifices and intermediate mix ratio, the spheres flow faster than the dumbbells.