The performance of a cyclone, with different vortex finders, was evaluated to examine the effect of the vortex finder shape on the characteristics of the collection efficiency. Four cylinder-shaped and six cone-shaped vortex finders were designed and employed to compare the collection efficiencies of the cyclone, at flow rates of 30 and 50 1/min. The cylinder-shaped-vortex finders had different diameters, i.e. 15, 11 and 7 mm, and the cone-shaped vortex finders had different cone lengths, i.e. 10, 25 and 45 mm, with 7 and 15 mm diameters at both ends of the cone. The collection efficiencies of the cone-shaped vortex finders were found to only be slight different, regardless of the cone length, which were higher than that of the cylinder-shaped vortex finder with a 15 mm diameter, but lower than that of cylinder-shaped vortex finder with a 7 min diameter. This result indicates that two cone-shaped vortex finders, with different diameters, had the collection efficiencies between those of the cylinder-shaped vortex finders with the same diameter, and that a smaller pressure drop per flow rate unit could be achieved for the cone-shaped design, but the cone length did not affect the collection efficiency and pressure drop of the cyclone. (C) 2003 Elsevier Ltd. All rights reserved.