(440d) Modeling Granular Segregation during Hopper Discharge

Ketterhagen, W. R., Purdue University

Granular materials containing particles of various sizes, shapes, and densities are present across a wide variety of industries including those handling pharmaceuticals, food and agricultural products, and chemicals. Differences in these particle properties may lead to segregation of the material upon transport or other handling. The flow of granular material within a hopper is one such process that may induce segregation. This segregation is problematic in that product quality is usually dependent on maintaining homogeneity of the blend.

The present work aims to investigate the causes and extent of segregation of granular materials during discharge from a hopper using the discrete element method (DEM). The granular material is modeled as bidisperse, frictional, inelastic spheres, and interstitial fluid effects are neglected. A soft-particle contact model is implemented using the hysteretic spring model of Walton and Braun [J. Rheol. 30, 949 (1986)] to model the normal forces, and Coulombic friction to model the tangential forces. The computational model has been previously validated through direct comparison with an experimental system of bidisperse glass beads.

This work investigates hopper flow segregation as a function of particle properties such as diameter ratio, mass fraction of fines, and coefficients of friction, as well as hopper geometries such as hopper wall angle and the fill height to width aspect ratio. Preliminary results show an increase in the extent of segregation for increasing diameter ratio and/or decreasing fines mass fraction. Also, differing hopper geometries tend to affect the shape of the mass fraction vs. mass discharged profile. Visualizations of the computational data help to elucidate the sources of the segregation during discharge.