Studies were carried out by suppressing the air core in a 100 mm DMC using a metal rod inserted through the spigot. The effect of the diameter of the inserted rod and its height of insertion on the Ep of the cyclone was studied. A spigot blocking ratio of 0.4 with 60% of free VF clearance gave the best separation efficiency. Multiphase CFD studies showed that the improved performance of the cyclone was because of (i) higher tangential velocity and hence higher centrifugal force acting on the particles (ii) lower radial and axial velocities at the VF reducing misplacement. (c) 2012 Elsevier Ltd. All rights reserved.