(550d) Understanding and Modeling Granular Segregation—Karl Jacob’s Vision

As large and small particles flow, small particles fall between large particles to segregate in lower portions of a dense granular flow while displacing large particles upward, a process known as “percolation.” Similarly, heavy particles segregate below light particles as they flow due to “buoyancy.” While many phenomenological studies of segregation have been performed, most focused on pattern formation, which is of academic interest, but not immediately applicable to industrial problems. Furthermore, previous models of segregation depend on obliquely defined or difficult-to-measure empirical parameters, making them impractical for process engineering problems. Over a decade ago, Karl Jacob had the vision to connect the academic interest in pattern formation and modeling with practical segregation problems in industry. This started as simple experiments for quasi-2D heap flow to understand size segregation typical of hopper filling. However, this prescient choice of a flow geometry provides a test bed with steady flow and segregation as well as a simple velocity field and segregation that is easily characterized. Because the heap flow geometry provides a wide range of flow and segregation conditions that are easily simulated and measured, this opened the potential for modification of the standard advection-diffusion equation to account for segregation. The resulting segregation model is physics-based, but, due to Karl Jacob’s insistence, it is readily applied to many practical flow geometries and conditions in industry. The model has been used to predict steady and transient segregation in chutes, rotating tumblers, hoppers, and shear cells and has been extended to density-disperse particles, multi- and polydisperse particles, non-spherical particles, and even particles varying simultaneously in size and density. Funded by The Dow Chemical Company, the Procter & Gamble Company, and the National Science Foundation.