ABSTRACT
Whenever granular mixtures are subjected to vibration, e.g. during processing or transport, segregation can generate undesired product non-homogeneity. Several experimental and modeling studies of segregation of vibrated spherical particles differing by sizes and/or density are reported in the literature (Kudrolli, 2004; Rosato, 2002). Two regimes are identified. In the “vibro-fluidised” regime, particles undergo mainly binary collisions, their energy is sufficient to widely explore the configuration space and buoyancy is proposed to explain segregation. In the “dense” regime, enduring contacts occur and different local mechanisms as void-filling, convection trap, and inertia are proposed to explain segregation. Beside “classical” Brazil-Nut effect bringing larger grains to the top, recent investigations also highlight Reverse BrazilNut effect that brings larger particles to the bottom of a mixture (Huerta, 2004). Granular media are dissipative non-equilibrium systems. Vibrated media are kept in motion by a continuous energy supply. At rest or during motion, granular media do not necessarily evolve toward a configuration that minimise the overall potential energy of the system. Local mechanisms as void-filling can generate size segregation and simultaneously increase the overall potential energy of the system.
