The main aim of the present study was to develop novel designs for conventional square cyclones in order to improve their separation efficiency using Computational Fluid Dynamics (CFD). Two novel design alterations were considered, and their performances were analyzed. First, the conical section of the conventional square cyclone was changed from single-cone to double inverted-cone. Second, the sharp corners of the main body were modified to rounded corners with different radiuses together with the use of the double inverted-cone. The results demonstrated that due to a smaller separation zone and higher particle concentration in the second lower cone, the square cyclone with rounded-corner and double-inverted cone produces higher separation efficiency among all simulated square cyclones under the same condition. Increasing the value of round corner (r/D) accelerated the flow inside the cyclone and led to a higher tangential velocity. Hence, a more intense centrifugal force field in the square cyclone was observed compared to single-cone square cyclone, and therefore, an improved collection efficiency was obtained. The performance of different cyclones for combined energy loss and collection efficiency was studied. A comparison of 50% cut-off diameters of different cyclones was presented, which revealed that the square cyclone with rounded-corner (r/D = 0.1), and double-inverted cone had the smallest 50% cut-off diameters for all considered pressure drops. The maximum 39.2% reduction of 50% cut-off diameter was obtained for this cyclone compared to the standard square cyclone. (C) 2020 Elsevier B.V. All rights reserved.