Predicting the Segregation Velocity in Granular Mixtures

A general model for the segregation velocity that is applicable across a range of flow geometries, flow conditions, and particle sizes is lacking. Analogous to the classic terminal velocity problem for a spherical particle in an otherwise quiescent viscous liquid, we consider the balance of segregation, which is buoyancy-like, drag, and weight forces on a single intruder particle in a granular flow, which allows the calculation of the segregation velocity because the drag force depends on the intruder particle velocity relative to bed particles. Recent advances in particle-scale modelling of the segregation and drag forces and their dependence on local granular flow conditions allow us to extend this force balance from a single intruder particle to particle mixtures over the entire particle species concentration range. This force-based approach correctly predicts the particle segregation velocity in idealized and natural size-bidisperse granular flow geometries for particle size ratios up to three based on discrete element method simulations. When incorporated in the well-established advection-diffusion-segregation continuum formulation, the force-based segregation velocity model has the potential to accurately predict size segregation in many relevant industrial and geophysical applications.