Determination of the flow/no-flow transition from a flat bottom hopper

Abstract

Hoppers and silos are widely used in storing powders in various industries, such as agricultural, chemical, food and pharmaceutical industries. It is of practical importance to design hoppers and silos to ensure smooth discharge of bulk solids from these devices, and to minimise the occurrence of arching, blockage and build-up of materials around the walls. However, due to the complex nature of bulk solids, arching behaviour of bulk solids in silos and hoppers is still not well understood. In this study, a combined experimental and numerical study was performed to explore the transition from non-flow to flow of bulk solids from a flat bottom hopper. Glass beads of various sizes were considered and the minimal orifice size through which these materials can be discharged was determined experimentally using a Flodex™ tester and numerically with discrete element modelling (DEM). The dependency of the minimal orifice size on the particle size was explored. Both the experimental and numerical results showed that the minimal orifice size is a function of the particle size, which can be well described using a modified Beverloo equation. It was also interesting to find that, even for spherical particles, dead zones could be formed during the discharge from the flat bottom hopper. Moreover, mono-layered dead zones were created when large particles were used.