Dense granular flows: Rheology and segregation

Flowing granular mixtures tend to segregate altering the flow characteristics and introducing an additional level of complexity. We use high speed video imaging to study the motion of individual particles in dense granular flows. Experimental results are presented for free surface flows of binary mixtures of equal size but different density particles. The flowing material exhibits some characteristics similar to glassy materials and these are highlighted. A model for density-driven segregation, developed in the framework of glassy systems, is presented. Segregation is found to depend on the effective temperature defined by the fluctuation dissipation relation. The predictions of the model agree well with experimental results.