Flow and clogging in a horizontal silo with a rotary obstacle

The external perturbation applied to a silo and the placement of an immobile obstacle before an exit are two common and effective ways to diminish clogging in the hopper/silo flow. Here, we incorporate the local perturbation into a fixed obstacle, and experimentally explore the effects of a rotary obstacle on clogging and the flowing characteristics in the horizontal silo flow driven by a conveyor belt. Even with a low spin rate, the total blocking probability that a particle constructs a stable blocking arch with its neighbors significantly drops. Correspondingly, the average flow rate of the particles through the exit abruptly rises, at least 1 order of magnitude better than that with an immobile obstacle and approaching the flow rate of continuous flow. The rotation enhances the breakage of clogging arches, which is responsible for improving the flowability in the horizontal silo. In addition, there always exists an optimal obstacle position at which the total blocking probability is minimal and the average flow rate peaks, regardless of the spin rate. Finally, clogging is relieved with the increase of the driving velocity of the conveyor belt, showing a “fast is fast” effect that is opposite to the “fast is slow” effect in other systems such as crowd evacuation and gravity-driven hoppers.