Sensitivity of granular segregation of mixtures in quasi-two-dimensional fluidized layers.

Size segregation is studied using a quasi-two-dimensional rotating cylinder system for mixtures of different size, near-spherical particles. Flow occurs only in a thin surface layer, whereas the remaining particles rotate as a fixed bed. In most of the systems studied, the measured radial weight fraction profiles in the bed show significant double segregation (a core of small particles as well as a thin layer of small particles at the periphery). The profiles are found to be sensitively dependent on the surface roughness of the particles in the mixture, and double segregation reduces with particle roughness. Double segregation is also sensitive to cylinder diameter and no double segregation is observed for the smaller diameter cylinders used. The system, however, shows two unexpected scalings: (i). the scaled profiles are nearly the same for different cylinder diameters, when the cylinder diameter to the cylinder length ratio is the same, and (ii). the profiles obtained are found to be insensitive to the size of the large particles in the mixture but depend strongly on the size of the small particles.