(673g) Particle Size Segregation in Granular Shear Flows

Gravity induced size-dependent segregation is a commonly observed, but usually undesired phenomenon in a variety of industrial processes. When a granular mixture with different size particles is sheared or vibrated, smaller particles have a tendency to fall into voids and segregate toward lower or interior portions of the flow. Inspired by recent work from our group on density-driven segregation, here we investigate the impact of different rheological characteristics on the size segregation of an "ideal solution" binary mixture, where a small number of intruders are immersed in an otherwise almost uniform bed. The Discrete Element Method is used to simulate the flow in a simple boundary-driven planar shear cell. Inside the cell is a mono-disperse particle packing that includes several smaller intruder particles which are used to measure size segregation for a variety of flow conditions: differing diameter ratios, shear rates, confining pressures and solid fractions. We find that in addition to the commonly used variables such as shear rate and solid fraction, pressure also has a profound but usually ignored effect on the segregation rate. Based on our simulation results, we propose a theoretical model linking size segregation with granular flow rheology.