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M. R. Swift, P. Sánchez, N. B. Burtally, M. Leaper and P. J. King.

Fluid-driven Separation in Binary Granular Mixtures.

Abstract: We shall describe a range of separation phenomena which occur in binary granular mixtures subjected to vibration in the presence of a fluid. Under vertical vibration, a fine bronze-glass mixture in air spontaneously segregates into glass-rich and bronze-rich "phases" which are extremely pure. Similar behaviour is also observed for mixtures of larger glass and bronze particles immersed in water. Under horizontal vibration, the mixtures segregate into stripes aligned perpendicular to the axis of vibration. To aid our understanding, we have developed numerical simulations that are able to capture many of the key features observed experimentally. From both experiment and simulation, we conclude that these strong separation effects result from the coupling between the granular motion and that of the fluid driven thorough the bed by vibration.