The Effects of Outlet Diameter on Particle Movement and Separation Performance of the Cylindrical Hydrocyclone

The outlet diameter of hydrocyclones is a critical structural parameter that impacts product distribution and separation performance, drawing significant attention. In this paper, the separation efficiency and particle motion behavior in the cylindrical hydrocyclone with varying spigot diameters and vortex finder diameters are systematically analyzed using a TFM model. The numerical results indicate that a larger spigot diameter and a smaller vortex finder diameter reduce the axial velocity and expand the external swirling flow region, while a smaller spigot diameter and a larger vortex finder diameter enhance the particle circulation flow ratio and the coarse particle circulation flow proportion, thereby increasing the cut size. Slightly reducing the spigot diameter and increasing the vortex finder diameter enhances the separation accuracy. Nevertheless, for Du = 0.075 D and Do ≥ 0.4 D, the recovery rate in the underflow remains below 50% for all particle sizes, exhibiting severe particle misplacement and loss of separation efficiency. For Du = 0.125 D, the reduction in coarse particle misplacement in the overflow is attributed to the abrupt changes in the coarse particle circulation flow proportion and medium particle circulation flow proportion. Generally, an appropriate coarse particle circulation flow proportion in the cylindrical hydrocyclone is beneficial for alleviating particle misplacement and improving separation accuracy.