Modelling the Multiphase Flow in Dense Medium Cyclones

Abstract

Dense medium cyclone (DMC) is widely used in mineral industry to separate solids by density. It is simple in design but the flow pattern within it is complex due to the size and density distributions of the feed and process medium solids, and the turbulent vortex formed. Recently, the so-called combined computational fluid dynamics (CFD) and discrete element method (DEM) (CFD-DEM) was extended from two-phase flow to model the flow in DMCs at the University of New South Wales (UNSW). In the CFD-DEM model, the flow of coal particles is modelled by DEM and that of medium flow by CFD, allowing consideration of medium-coal mutual interaction and particle-particle collisions. In the DEM model, Newton's laws of motion are applied to individual particles, and in the CFD model the local-averaged Navier-Stokes equations combined with the volume of fluid (VOF) and mixture multiphase flow models are solved. The application to the DMC studies requires intensive computational effort. Therefore, various simplified versions have been proposed, corresponding to the approaches such as Lagrangian particle tracking (LPT) method where dilute phase flow is assumed so that the interaction between particles can be ignored, one-way coupling where the effect of particle flow on fluid flow is ignored, and the use of the concept of parcel particles whose properties are empirically determined. In this paper, the previous works on the modelling of DMCs at UNSW are summarized and the features and applicability of the models used are discussed.