Granular Flow and Segregation

Granular Flow: A rich variety of phenomena occur in granular flows including mixing or segregation of particles of varying sizes or densities, chaotic advection, and pattern formation.  In collaboration with Julio M. Ottino and Paul B. Umbanhowar, we use measurements, simulations, and theory to understand and characterize canonical flows such as granular flow in partially-filled rotating drums and heaps.  The image at left shows a simulation of the segregation of particles of two sizes in a rotating tumbler.  See publications here.

Segregation of Particles with Different Sizes on a Heap: A mixture of large gold particles and small red particles fall onto and flow down a heap. In the thin flowing surface layer, the small particles fall between the large ones. As a result, the small particles deposit on the upstream portion of the heap, while large particles continue further down the heap to deposit on the downstream portion of the heap. By the end of the video, the result is that the small and large particles become segregated from one another. In many situations industry, such segregation is undesirable. Our research focuses on predicting and preventing segregation of particles that differ not only in size but also in density, shape, and cohesive properties.

Modeling Stratified Segregation on a Heap: In the experiment on the left, a mixture of large 2 mm blue particles and small 0.5 mm red particles are fed onto the top left of a quasi-2D heap, alternating between a fast feed rate and a slow feed rate, resulting in layers of small and large particles. The model results on the right closely match the experiments, demonstrating the effectiveness of the advection-diffusion-segregation approach that we have developed, even for complicated transient flows. See Modeling Periodic Stratified Segregation in Granular Heap Flows