Pressure independence of granular flow through an aperture

TL;DR

This study experimentally shows that granular flow rate through an aperture depends on exit velocity rather than pressure, challenging previous assumptions and providing new insights into granular flow dynamics.

Contribution

The paper introduces a horizontal conveyor belt setup to independently control and study the effects of velocity and pressure on granular flow through an aperture.

Findings

Flow rate is proportional to belt velocity.

Flow rate is independent of the number of disks in the container.

The setup allows analysis of system dynamics from a single image.

Abstract

We experimentally demonstrate that the flow rate of granular material through an aperture is controlled by the exit velocity imposed to the particles and not by the pressure at the base, contrary to what is often assumed in previous works. This result is achieved by studying the discharge process of a dense packing of monosized disks through an orifice. The flow is driven by a conveyor belt. This two-dimensional horizontal setup allows to uncouple pressure and velocity and, therefore, to independently control the velocity at which the disks escape the horizontal silo and the pressure in the vicinity of the aperture. The flow rate is found to be directly proportional to the belt velocity, independent of the amount of disks in the container and, thus, independent of the pressure in the outlet region. In addition, this specific experimental configuration makes it possible to get information on the system dynamics from a single image of the disks that rest on the conveyor belt after the discharge.