Despite of the widespread use of hydrocyclones, their accurate design is often difficult because there exist many mathematical relationships to predict the separation efficiency and the pressure drop based on semi-empirical models which are restricted to particular cyclone geometry and operating conditions from which they are deduced. Some numerical approaches based on computational fluid dynamics (CFD) have been performed to describe the flow field. The present investigations deal with problems occurring when applying CFD methods to hydrocyclones and some basic information is given to yield reliable results concerning the velocity and pressure distribution and the grade efficiency curve as a fundamental basis in the design of these apparatuses. (C) 2004 Elsevier B.V. All rights reserved.