Many empirical models for predicting the particle separation efficiency of cyclone separators have been presented by different investigators. but they are often limited in their use to the particular type of cyclones on which they were developed. This paper describes theoretical models and a numerical model for the analysis of the fluid flow and particle separation of cyclones and how them may be used in the design of ne types of cyclones. The governing fluid and particulate flow equations have been analysed and numerically solved in order to predict the fluid flow and particle separation in cyclones. In addition, the key design parameters for the cyclones have been discussed as to their effect on the overall performance of the cyclone and general recommendations for the engineering design of cyclones have been suggested. Copyright (C) 2002 John Wiley Sons, Ltd.