Granular flow through an aperture: influence of the packing fraction

TL;DR

This study investigates how the initial packing fraction influences the flow rate of granular materials discharging through an aperture on a conveyor belt, revealing that flow rate variations are directly linked to packing density changes.

Contribution

It provides new insights into horizontal granular flow dynamics, emphasizing the role of packing fraction, which differs from traditional vertical gravity-driven systems.

Findings

Flow rate depends on packing fraction.

Flow velocity at the outlet remains constant despite packing changes.

Packing fraction modifications directly affect flow rate.

Abstract

For the last 50 years, the flow of a granular material through an aperture has been intensely studied in gravity-driven vertical systems (e.g. silos and hoppers). Nevertheless, in many industrial applications, grains are horizontally transported at constant velocity, lying on conveyor belts or floating on the surface of flowing liquids. Unlike fluid flows, that are controlled by the pressure, granular flow is not sensitive to the local pressure but rather to the local velocity of the grains at the outlet. We can also expect the flow rate to depend on the local density of the grains. Indeed, vertical systems are packed in dense configurations by gravity but, in contrast, in horizontal systems the density can take a large range of values, potentially very small, which may significantly alter the flow rate. In the present article, we study, for different initial packing fractions, the discharge through an orifice of monodisperse grains driven at constant velocity by a horizontal conveyor belt. We report how, during the discharge, the packing fraction is modified by the presence of the outlet and we analyze how changes in the packing fraction induce variations in the flow rate. We observe that variations of packing fraction do not affect the velocity of the grains at the outlet and, therefore, we establish that flow-rate variations are directly related to changes in the packing fraction.