The effects of cone dimension on cyclone performance characteristics were investigated in this study. Collection efficiencies for three cyclones with different cone bottom diameters were measured as a function of particle size and flow rate. The measurement results suggest that flow rate strongly influenced the efficiency values and the sharpness of the efficiency curves. Cone size, on the other hand, only has significant effect on collection efficiency. When the cone opening is larger than the gas outlet diameter, reduction in cone size results in higher collection efficiency without significantly increasing the pressure drop. Experimental data were compared with the predictions of Earth's theory, Leith and Licht's theory, and Iozia and Leith's logistic method. Results show that only Earth's theory and the logistic method of Iozia and Leith predict the efficiency curve reasonably well. However, none of the three theories correctly and sufficiently takes into account the effects of cone size. (C) 2001 Elsevier Science Ltd. All rights reserved.