CFD-DEM study of segregation and mixing characteristics under a bi-disperse solid-liquid fluidised bed

In this work, a recent smoothed CFD-DEM model is employed to study the segregation and mixing behaviours in a bi-disperse solid–liquid fluidised bed (SLFB) with different superficial liquid velocities and wide size ratios. Here, the poly-disperse drag model is applied, and its validity and advantage are confirmed. Besides, the qualitative and quantitative characteristics are systematically studied using a variety of indices, while the intermixing behaviour in the transition zone is investigated. The results show that segregation degree is well quantified by the mixing index, and the circulation motion of particles and liquid is confirmed in the transition zone. The more drastic motions can be observed in the transition zone under lower superficial velocities or size ratios. Furthermore, the force analysis in terms of the drag force and collision force indicates that the combined contribution of hydrodynamics and collision is the main underlying mechanism of segregation behaviour in the bi-disperse SLFB.