(273f) Methodology for Identification of Interaction Parameters for DEM Studies

Discrete Element Method (DEM) is rapidly expanding as a valuable approach to describe various unit operations in the pharmaceutical, food and mining industries such as mixing, milling, fluidization, transport, etc. However, accurate identification of interaction parameters (friction and restitution coefficients) remains a challenge in all these applications. The issue is even more challenging considering that new materials are being rapidly developed with broad particle size distributions, varying particle shapes, as well as broad range of bulk material properties. Direct experimentation using specific unit operation of interest with each individual powder yielding trustworthy results is possible, but is expensive both in terms of facilities and labor required. At the same time, results of experiments with a restricted range of experimental configurations and selected materials cannot be justifiably extended to predict behavior of powders that have not been tested directly. 

The objective of this work is to develop a simple and easy to use methodology to quantify the particle-particle and particle-geometry interaction parameters for DEM studies. Direct experimental validation is the key aspect of this approach. To enable the direct comparisons of experiments and calculations we work with a carefully designed experimental configuration with a relatively small number of particles (~20,000-30,000), for which systematic changes of powder processing parameters can be readily implemented experimentally as well as described in DEM. The experimental set-up consists of a small vibrating hopper in which the powder is loaded. The number and size of the particles exiting the hopper can be tracked illuminating the powder stream with a laser sheet and using a photomultiplier tube to register the pulses of scattered light. For these initial validation experiments, we use spherical powders with different surface properties, densities, and particle size distributions, including a monodispersed powder. 

A parametric study investigating behavior of different powders both experimentally and computationally will be discussed.   The particle size distribution is directly represented in DEM.  In both model and experiment, the oscillation frequency and amplitude are varied and respective feed rates and sizes of the particles fed in real time are monitored.  The sensitivity of the DEM predictions to specific values of friction and restitution coefficients is investigated. The effectiveness of different particle interaction models in accurately predicting the experimental data is tested.