CONVECTION AND SIZE SEGREGATION IN A COUETTE-FLOW OF GRANULAR MATERIAL

We have investigated the size segregation of a binary mixture of spher ical glass particles in a Couette geometry, where the cylinders are ma de of smooth glass and the flow is generated by the shearing motion of the inner cylinder. The trajectories of 1, 2, and 3 mm glass particle s, placed at the bottom of the cell, were followed as they moved throu gh a 1 mm medium. We observe convective motion of the particles in whi ch particles rise at the outer radius and fall at the inner radius. Th e horizontal and vertical speeds of 2 and 3 mm glass particles, initia lly at the cell bottom, as a function of the inner cylinder speed were determined and the onset of turbulent motion measured by processing i mages. While in all cases the larger particles rose to the top and rem ained on the surface as rotation continued, the particles comprising t he medium appear to go through a convectivelike motion. The effect of interstitial fluid, in this case air, was studied by repeating the exp eriments in vacuum. We did not detect any significant changes in the r esults.