In this study, a computational fluid dynamics is used to predict and evaluate the effects of vortex finder shape and diameter on cyclones performance and flow field. The Eulerian-Lagrangian computational procedure is used to predict particles tracking in the cyclone. The flow field is calculated using 3D Reynolds-averaged Naveir-Stokes equations. The Reynolds stress transport model (RSTM) is used to simulate the Reynolds stresses. The Newton's second law is used to study the particles trajectory with modeling the drag and gravity forces acting on the particles. The velocity fluctuations are simulated using the discrete random walk (DRW). Four different cylinder-shaped and six cone-shaped vortex finders are simulated for various flow rates of 30, 50 and 701/min. The cylinder-shaped vortex finders have different diameters, i.e. 15, 11 and 7 mm, and the cone-shaped vortex finders have different cone lengths, i.e. 10, 25 and 45 mm, with 7 and 15 mm diameters at both ends of the cone. The particles size range is 0.5-3 mu m. The details of the flow field are studied in the cyclones and the effects of the different vortex finders are observed. The numerical results are compared with the experimental data and good agreement is observed. (c) 2007 Elsevier B.V. All rights reserved.