Title: Mixing, Segregation, and Signatures of Chaos in Tumbled Granular Materials
Speaker: Dr. K. Hill
Speaker Info: Northwestern U.
Mixtures of granular materials tend to segregate due to small differences in size and/or density, an obstacle for processing granular materials which also provides fascinating problems in pattern formation. Well-known examples of this occur in horizontal rotating drum mixers partially filled with mixtures of granular materials. When particles differing in size (or density) are rotated in a partially-filled drum, the smaller (or more dense) material will quickly radially segregate toward the axis of rotation and eventually segregate into bands along the axis. Radial segregation has been viewed as a necessary predecessor to axial segregation, which has recently motivated studies of radial segregation isolated in a 2-d mixer. We have performed segregation experiments in circular and non-circular 2-d mixers; non-circular mixers have been found to induce chaotic advection in the granular systems, which, in general, improves mixing efficiency. However, chaotic advection interacts in non-trivial ways with density and size segregation of granular materials. In non-circular mixers the final state of segregation consists of complicated patterns which resemble the computationally derived Poincare sections for the mixers. The patterns are sensitive to the fill level, particularly near 50%, where several bifurcations occur in the Poincare sectionsDate: Friday, February 19, 1999