Particle segregation in vibrofluidized beds due to buoyant forces

We utilize two-dimensional discrete element computer simulations to investigate the equilibrium position of an impurity in a vibrofluidized bed of otherwise homogeneous particles. The steady state equilibrium height of the impurity increases with increasing vibration velocity amplitude and decreases with the impurity to the surrounding particle density ratio. A simple model whereby the impurity weight is balanced by a "buoyant" force due to the surrounding particle impacts makes a good prediction of the impurity position.