AVALANCHE-MEDIATED TRANSPORT IN A ROTATED GRANULAR MIXTURE

A binary mixture of granular materials in a horizontal, rotating tube segregates under certain circumstances into an alternating pattern of bands of two types along the tube axis, each type being rich in one id f the components. The pattern coarsens with time through band shrinkin g and merging, until a steady state characterized by some average band width is reached. We have studied experimentally the long-term evoluti on of segregation patterns in sand-glass bead mixtures. We observe tha t during coarsening, the two types of band evolve differently, indicat ing that another transport mechanism is at work besides diffusion. We propose that glass beads are transported axially due to ''avalanche wa ves,'' a hallmark of the discontinuous flow characterizing sand-rich b ands.