Effects of vibration method and wall boundaries on size segregation in granular beds

Abstract

This paper investigates the rise rate of a large impurity in an otherwise homogeneous granular bed subject to discrete and continuous vertical oscillations. Experiments and two-dimensional discrete element computer simulations reveal that the impurity rise rate depends upon the oscillation method when side-wall convection effects are negligible. For discrete oscillations the rise rate increases monotonically with the oscillation velocity amplitude while for continuous oscillations the rise rate reaches a maximum value at a critical velocity amplitude. The rise rate trends correlate with changes in the bed void fraction. When side-wall convection effects are present, the rise rate of the impurity increases linearly with the oscillation velocity amplitude regardless of the vibration method. The results from the studies presented here reconcile the seemingly inconsistent results reported previously in the literature.