Laboratory experiments with dry particles of different sizes and different densities, and different particle-liquid mixtures flowing down rectangular chutes show the relative importance of segregation mechanism. In uniform steady flow experiments with binary mixtures of small and large particles, the small particles fall downward and the large particles migrate upward. In slow, dry, frictional flows, the downstream segregation is so efficient that zones of 100percent small and large particles separated by a concentration jump form. In rapid, dry, collisional flows, segregation is less efficient because of diffusive mixing. Diffusive mixing smoothes vertical concentration profiles so that concentration jumps blur or disappear. The presence of a viscous fluid inhibits size segregation. Little to no segregation occurs when liquid density matches particle density.
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