Effect of particle shape on silo discharge

Silo discharge rate of rod-like and ellipsoidal particles is compared in laboratory experiments. We focus on how the flow rate is changing with particle aspect ratio a/b. Our experimental investigations for ellipsoids are complemented by numerical simulations using the Discrete Element Model (DEM). For ellipsoids the flow rate is a non-monotonic function of a/b with slightly elongated or slightly flat ellipsoids discharging the fastest. DEM simulations show that both the packing fraction as well as the particle velocity has a nonmonotonic aspect ratio dependence, thus both contribute to the non-monotonic tendency of the flow rate. When comparing the flow rate of rods with ellipsoids, we get very similar values for similar aspect ratios. On the contrary, when comparing the packing fraction we find a noticeable difference: it is about 10% lower for rods than for ellipsoids. This suggests that the particle velocity for rods should be larger by about the same amount, so that the product of these two factors results in the same flow rate for the two types of grains.