NU 2017-041
INVENTORS
Paul Umbanhowar
Yi Fan
Richard Lueptow*
SHORT DESCRIPTION
A process for layering mixtures of granular materials with different physical properties onto static regions by surface flow
BACKGROUND
Segregation and mixing of disperse granular materials (differing in size, density, and shapes) have important implications in situations ranging from material handling in industry to natural phenomena. In industry, segregation is frequently encountered in processes involving handling bulk solids such as ores, polymers, food, and pharmaceutical materials. In most cases, segregation of an initially well-mixed granular mixture is undesirable, because it impacts the efficacy of later processes or the quality of final products. Therefore, understanding the mechanisms of granular segregation and developing efficient mixing technologies are of great importance for industrial applications. As such, the understanding of segregation in flowing granular materials has been advanced by extensive experimental, computational, and theoretical studies over the past several decades. Most studies have focused on segregation in steady granular flows with relatively simple kinematics and time invariant pattern formation. As the particle size ratio increases, segregation becomes stronger, with a clear interface between the small and large particle enriched regions, causing inhomogeneity in subsequent processes such as hopper discharge or chute transfer. Counter-balancing mechanisms, such as altering particle characteristics like density and inelasticity, adding a small amount of liquid to dry particle mixtures to increase cohesiveness, or completely submerging the particles, can each help minimize segregation. However, these methods are not always feasible in industrial applications.
ABSTRACT
Northwestern researchers have focused on size segregation of dry spherical particles in industry applications. They developed a novel process for layering mixtures of granular materials with different physical properties such as size, shape, and density onto static regions by surface flows. The method helps reduce segregation by creating layers of different particle types in common industrial processes by utilizing particulate matter flows including the filling of hoppers, boxes, and other enclosed vessels as well as the formation of free-standing piles. While unsteady flows of granular media are ubiquitous and yet have remained largely unexplored, the researchers applied unsteady flows to control the segregation pattern of granular materials and enhance overall mixing. This approach improves the manipulation of granular material, allowing the user to skip additional mixing steps and combine raw materials without additional preprocessing such as grinding or sieving. Based on the Danckwerts intensity of segregation and a preliminary hopper discharge study, they demonstrated that the flow-modulated stratified pattern can reduce the overall inhomogeneity in a heap leading to better mixing during hopper discharge, which has great potential to limit particle segregation in many industrial processes.
APPLICATIONS
ADVANTAGES
PUBLICATIONS
Xiao H, McDonald D, Fan Y, Umbanhowar P, Ottino J and Lueptow R (2017) Controlling granular segregation using modulated flow. Powder Technology. 312: 360-368.
IP STATUS
US patent application has been filed