UNS: Controlling mixing and segregation of granular media using unsteady flows

Overview: Granular flow is ubiquitous in industry and nature. Polydisperse materials, i.e., consisting of particles with different size, density, or other material property, tend to segregate, or de-mix when they flow. Segregation impacts particle and powder processing in many industries as well as natural phenomena such as sediment transport and debris flow. Understanding and modeling segregation and mixing in granular flows have been advanced over the last two decades by an array of experimental, computational, and theoretical studies, but most studies have focused on steady flow. Unsteady granular flow is, however, common. Though it has been studied for avalanches in heap flow and fingering in inclined chute flow, the kinematics and dynamics of unsteady flows remain largely unexplored and, in our view, unexploited. The proposed research focuses on the segregation, mixing, and kinematics of unsteady polydisperse granular flow. In contrast to past research on intrinsically unsteady flow, this research concentrates on controlled flow modulation and its impact on segregation, kinematics, and pattern formation in granular systems. The goals of the research are twofold: (1) Develop new techniques to control segregation and improve mixing by modulating granular flows. (2) Examine the interplay between kinematics and segregation of modulated granular flow to develop a theoretical framework to predict spatial particle segregation distributions. This research will focus on two canonical granular flows: bounded heap flow and rotating tumbler flow. ULTIMATE OBJECTIVES: Devise techniques to control segregation and improve mixing of polydisperse materials by flow modulation; develop a theoretical framework for segregation and mixing in unsteady granular flow. Intellectual Merit: Most processing approaches for granular materials are ad hoc, often with stringent limitations on flow geometries, particle properties, and operating conditions. Our preliminary results show that it is possible to control the mixing and segregation of polydisperse granular materials with flow modulation, but a much better understanding of unsteady granular flows is needed to fully exploit this approach. The proposed research is potentially transformative in three ways. FIRST, new techniques will be developed to improve handling and processing of polydisperse particles by intentionally generating and controlling unsteady granular flow. The intent is to guide operation of industrial granular materials processes and systems by providing methodologies that apply over a wider range of operating conditions with more precise control. SECOND, these practical results will be supported by a companionm continuum-based theoretical framework for segregation and mixing in unsteady polydisperse granular flows. The model will account for unsteady flow, segregation, and collisional diffusion, and thus have broad applicability to and predictive capability for other unsteady granular flows. THIRD, the knowledge of kinematics and segregation in unsteady granular flow gained through experiments and simulations in this research will provide an improved intellectual foundation for the fundamental physics of flow, segregation, mixing, and pattern formation in granular systems. Broader Impacts: In 2005, the journal Science identified the flow of granular materials as one of the 125 big questions in science. Granular flows are important in disciplines ranging from geophysics to industrial processing, from landslides on Mars to mixing ingredients in pharmaceuticals. The prevalence of granular