A comprehensive multiphase model of cyclone separators using Computational Fluid Dynamics is under development. The model is capable of predicting velocity profiles, flow splits, air core position and efficiency curves in classifying hydrocyclones. The model approach uses the Mixture model with the granular options and large eddy simulation (LES) to resolve the turbulent mixing of the particles. Multiphase simulations of Hsieh's [Hsieh, K.T., 1988. A phenomenological model of the hydrocyclone, Ph.D. thesis, University of Utah] data show a very good prediction of the cyclone efficiency curve. Whilst further model development is needed, the approach is showing promise as a cyclone design tool. © 2006 Elsevier Ltd. All rights reserved.