An analytical model was developed to predict the fractional efficiency of a uniflow cyclone with a tangential inlet. The analysis showed that the separation efficiency is a function of particle Stokes number and the geometry of the cyclone body. Six sets of experiments were conducted under different conditions to validate the model. The experimental fractional efficiencies were determined by the total mass efficiency and the corresponding size distributions measured by using an offline particle sizer. Overall the experiments agreed with the modeling results well. Both model and experiments showed that the efficiency of this cyclone reached 99.5% and above when Stk > 1.0. (c) 2007 Elsevier B.V. All rights reserved.