Computational fluid dynamic (CFD) methods are used to investigate the enhancement of the solid-gas separation efficiency by adding tangential chambers to the conical section of a conventional cyclone separator. It is shown that the addition of the tangential chamber enhances the separation of the particles near the conical section wall, and hence the overall separation efficiency, particularly for small particles (1-3 mu m). This enhancement occurs with only an 8% increase in the pressure drop between the inlet and outlet of the cyclone. The effects of the inlet velocity and the number of the tangential chambers on the separation efficiency are studied to find the optimum conditions. It is shown that the increase in the velocity enhances the efficiency at the expense of an increase in the pressure drop (the increase in the inlet velocity from 14 to 20 m/s doubles the pressure drop). The model also shows that the addition of one tangential chamber produces a lower dissipation rate of turbulence in the cyclone as compared to multiple chambers, and hence a higher separation efficiency. The efficiency of the proposed geometrical modification is also compared against the conventional cyclone design and that with another geometrical modification reported in the literature (i.e., a cyclone with an elongated conical length). The results reveal that the proposed modification in this paper enhances the separation efficiency for small particles (less than 3 p=mu m) up to 50% compared to the conventional and the elongated designs and 15% for large particles (larger than 6 mu m) compared to the conventional design. The proposed modification was also compared to the conventional design in terms of the erosion rate of the cyclone walls, which is increased by 50%.