Effects of Diameter and Aspect Ratios on Particle Separation Efficiency in Hydrocyclones

Abstract

Hydrocyclones are widely used for solid-liquid separation, but their performance is highly sensitive to the geometric design. Previous studies often focused on individual structural parameters; however, the combined effects of the vortex finder diameter and aspect ratios on the internal flow field and particle separation behavior remain insufficiently clarified. This study conducted three-dimensional numerical simulations using the realizable k-epsilon turbulence model, combined with the discrete phase model. The particle size distribution behaves according to the Rosin-Rammler function. Seven different geometries were evaluated under identical operating conditions to systematically investigate how the diameter and aspect ratios influence the internal vortex structures and separation behavior. A decrease in the diameter ratio enhances the dominance of the outward centrifugal forces, which increases the downward discharge of coarse particles but also results in greater liquid entrainment through the underflow. Conversely, larger diameter ratios strengthen the secondary vortex and promote upward flow. However, this also leads to decreased recovery of fine particles due to weakened centrifugal action. Adjusting the aspect ratio effectively mitigates these tradeoffs. Increasing the cone length enhances the residence time, stabilizes the upward vortex, and improves the separation of fine particles. Although the overall separation performance shows diminishing returns beyond a certain aspect-ratio threshold, the recovery of fine particles continues to improve. The results reveal that a balance between centrifugal and drag forces is essential, which is achieved through coordinated control of the vortex finder diameter and cone geometry. This balance is critical for maintaining stable flow fields and high efficiency in fine-particle removal. The findings provide practical design guidance for hydrocyclones, particularly in applications that require enhanced recovery of fine particles and stable multiphase flow behavior.