Numerical and Experimental Studies of Granular Materials in the Quasi-Static Regime

In the chemical and process industries, a large percentage of granular materials are handled and produced on a daily basis. Indeed, such materials are widely used in powder-based unit operations such as granulation and drying; fluid catalytic cracking processes; coal gasification [1]. Those materials exhibit a broad range of intricate behaviours and might vary in size and shape; in addition, moisture can be present which might lead to particles agglomeration. In our work, we propose a numerical simulation at the particulate scale together with an experimental study that will allow us to understand the effects of those parameters on the flow behaviour of granular materials. This study will ideally help industrial practitioners handle and produce particulates in an efficient and less costly way.
Among all the methodologies available for the measurement of granular materials' flow properties; the shear test is a preferred method due to the relative simplicity of its procedure [2]. In this test, the granular material is subjected to a given applied normal pressure (normal stress s) and the stress needed to generate shear (shear stress t ) leading to either compaction or dilation of the granular bed is evaluated. In this study, the shear cell apparatus of an automated powder rheometer (FT4 powder rheometer), developed by Freeman Technology Ltd. (Castlemorton Common, Worcestershire, UK), is used in order to generate experimental shear test data (s versus t) obtained with dry monodisperse spherical glass beads (0.5mm diameter). We also perform the discrete element method (DEM) simulations of simple shear flows of glass beads in a periodic domain by applying Leeds-Edwards boundary conditions [3,4]. In these simulations, the particle-particle friction coefficient is a lump parameter, which is calibrated using the shear test data. This will serve as a base case for the modelling of the shear response of cohesive particles.

Once the DEM simulation is calibrated and validated, constitutive models for particles stresses will be proposed in order to simulate granular flows in industrial-scale applications. These proposed models will be revisited by undertaking further experimental studies of granular materials with variable morphological properties (size and shape) and moisture content.