Segregation by flow in quasi 2D piles

D. RODRÍGUEZ; BENITO J. G.,; IPPOLITO, I; HULIN, J. P.; VIDALES A.M; UÑAC, R.O.;

Córdoba

Workshop; XIII Latin American Workshop on Nonlinear Phenomena; 2013

Stratification, mixing and layering processes have been studied during the build-up of quasi-2D piles from two different mixtures of grains of different diameters (1mm glass beads and 3mm glass beads or coriander seeds). The domains of existence of the different flow regimes obtained for the two sets of beads as a function of the relative volume flow rates of the two species and of the fall heights have been compared and the influence of the flow regimes on the time dependence of the mean slope of the pile has been studied. The experiments, show in particular, that segregation may be complete when the larger grains are coriander seeds while some amount of mixing is always observed for glass beads, even though the ratio between the sizes of the particles is the same in both cases. The layering regime could be observed using glass beads of same spherical geometry and density but with two different diameters: it is is characterized by the large amplitude of the variations of the slope of the pile. No layering is observed when coriander seeds of same size replace glass beads as the large particles. The local processes involved in these regimes have been analyzed quantitatively : the characteristic velocities of the different types of displacements of the grains have in particular been determined from spatiotemporal diagrams of the variation with time of the profile of the free surface. Avalanches were only observed in the layering regime and play an important part in the development of the layers.