The performance of a novel cyclone separator with a cone made of porous sintered metal was compared with that of a conventional design with a cone made of acrylic resin. Controlled injection of clean air through the porous cone is proposed as a new method to control the cut size and reduce powder deposition on the cone. In the experiments, when clean air was not injected through the porous cone, the cut size and the amount of powder deposited on the porous cone were greater than for the acrylic resin cone. However, the introduction of adequate clean air through the porous cone simultaneously reduced the cut size and the powder deposition to less than those with the conventional cone. The revised horizontal-flow model revealed that this occurred because the injected clean air enhanced the tangential velocity of the fluid near the cone surface by reducing the surface's apparent friction factor. It was also confirmed that the clean air ratio can be used to control the cut size while keeping the separation accuracy constant. Further, the novel model could also estimate the dependence of the 50% cut size on the clean-air ratio. (C) 2011 Elsevier B.V. All rights reserved.