The effects of top blade rotation of hydro-cyclones on particle classification performance were examined experimentally and via a simulation study. It was noticed that the cut size of a hydro-cyclone decreases as the rotational speed of the top plate increases. Compared to the standard case without rotation, the accuracy of classification with top plate rotation increases under the wide range of operational conditions. Newly proposed type-D cyclones with a special blade indicated the smallest cut size with a high accuracy of classification. The increase of classification accuracy is due to the production of outward radial flow near the top plate and this result was simulated by a CFD calculation. The computer simulation also agreed qualitatively with the experimental data. (C) 2006 Elsevier B.V. All rights reserved.