This paper studies a dynamic cyclone with a rotary impeller inside experimentally and numerically. The experiment mainly focuses on the separation efficiency, while the numerical simulation describes the flow field in the dynamic cyclone. The discrete phase model (DPM) is also used to predict the fractional efficiency of the dynamic cyclone, and the predictions are compared with the experimental results. The dynamic cyclone has been demonstrated to be very helpful for increasing the separation efficiency when the impeller rotates at greater speeds. The simulation predictions prove that the tangential velocity distributions are mainly dominated by the rotational speed for the region of impeller and dominated by the inlet velocity for the region outside of the vortex finder. Both the experiment and simulation show that the effects of inlet velocity on the separation efficiency are different for different rotational speeds. (c) 2007 Elsevier B.V. All rights reserved.