Two small cyclones, made of aluminum and glass, with different dimensions were employed to understand the effects of minor flow on cyclone efficiency, and then to evaluate their potential usage as particle concentrators. Minor flow is airflow from the bottom of the cyclone where the dust collects in a conventional cyclone. A cyclone having a minor flow is referred to as a virtual cyclone in this study. The difference between a conventional cyclone and a virtual cyclone is that the latter has a minor flow while a conventional cyclone does not. In order to study their performance systematically, both virtual cyclones were tested under different operating conditions. The major flow efficiency curve, 50% cut-off diameter and pressure drop, were measured as a function of the ratio of the minor flow to the inflow. Compared to a conventional cyclone, the virtual cyclone showed a higher major flow efficiency and a smaller 50% cut-off diameter under the same operational conditions. As a final step, the concentration factor, the factor by which a given size is concentrated in the minor flow, was calculated as a function of particle diameter. It was found that at a fixed inflow rate, the concentration factor first increased and then decreased as particle diameter increased. This study shows that the virtual cyclone has the greatest potential for concentrating particles in the region of 50% cut-off diameter. (C) 2002 Published by Elsevier Science Ltd.