Instabilities in Granular Taylor-Couette Flow Benjamin J. Glasser, Department of Chemical & Biochemical Engineering, Rutgers University, Piscataway, NJ 08854 Understanding of many aspects of particulate processing operations is important for the petroleum industry. At the same time, granular processes are often afflicted by poor performance due to erratic flow, density waves, jamming, undesired segregation, and structural failure. In fluids, analysis of paradigmatic or model experiments, like Benard, Couette, Taylor-Couette, and Kelvin-Helmholtz, has served to uncover aspects of shear transmission that have led to a better understanding of flows of engineering importance. For granular flows, we believe improved understanding will hinge on analysis of analogous paradigmatic or model experiments. The focus of this work is Taylor-Couette flows which are one of the simplest model geometries encompassing both shear and boundary interactions – essential ingredients of practical flows. Taylor-Couette granular flow is examined using a combination of experiments, particle dynamic simulations (see figure below) and continuum mechanics/kinetic theory. Our focus is on instabilities leading to mesoscopic variations in density and flow properties and spatio-temporal structures. By determining the nature and magnitude of these instabilities we anticipate more reliable methods of scale-up and assurance of process performance. Going beyond steady states to investigate time-dependent flows will also allow us to test and further develop constitutive equations that describe granular flows. Implications for segregation of binary particulate mixtures with equal diameter but different mass particles. The coefficient of particle-particle restitution decreases from 0.99 to 0.90 to 0.75 from the left to the right.