Bimodal frequency distribution of granular discharge in 2D hoppers

As a classical example of granular flow, gravity-driven hopper flow has been studied for decades, but an in-depth understanding of its fluctuation is still lacking, especially at small-scale and short-term. In this experimental and numerical study, the time interval (t(Delta)) between the discharging of two consecutive grains from hoppers under a series of geometrical and operating conditions is characterized by its probability density function (PDF). By ensemble averaging over a large number of cases, the PDF from simulation and experiments was found to be consistent but totally different for small and big orifices. Three modes of particle discharging were found and each matches a section of the PDF, with two of the modes found in simulating the discharging of hard sphere gas through an orifice, which suggests a similar mechanism behind the two phenomena. These findings may be helpful to the designing and operation of high-precision feeding system, such as in pharmaceutical industries. (C) 2021 Elsevier Ltd. All rights reserved