Effects of apex/vortex ratio on the isobaric surface and particle separation performance of a hydrocyclone

Isobaric surface is a characteristic feature generated during particle motion in the hydrocyclone. Its pattern and position can directly affect the separation performance, which has rarely been studied. In this study, the isobaric surface and flow field in the hydrocyclone with different apex/vortex ratios were investigated in-depth via numerical analysis, and the effects of air core on axial velocity and tangential velocity were explored. On that basis, the effect of apex/vortex ratio on the hydrocyclone's separation performance was analyzed. The results showed that both pressure and tangential velocity increased with the increasing apex/vortex ratio. Through theoretical study and numerical analysis, the isobaric surface in the forced- and free-vortexes showed parabolic and hyperbolic patterns, respectively. As the apex/vortex ratio increased, the isobaric surface moved towards the center of hydrocyclone, suggesting the expansion of free-vortex region, the shrinkage of the forced-vortex region, and thus the failure in particle gradation and separation. Air core can lead to the fluctuation of both axial and tangential velocities. The fluctuation frequentness increased with the apex/vortex ratio, causing the disorder of flow field and the reduction of separation efficiency. At an apex/vortex ratio of 3/2, fluid can only move downwards and the hydrocyclone no longer played the role of gradation. As the apex/vortex ratio increased, the content of fine particles in the underflow increased drastically, and most of coarse particles were discharged from the underflow port. In contrary, the cutting capability and separation precision increased with the decline of the apex/vortex ratio. Therefore, in order to obtain high-quality product, the apex/vortex ratio should be as small as possible under the premise of satisfying the separation requirement. [Display omitted] •The effect of isobaric surface on separation performance was studied.•The accuracy of the model used in the numerical simulation was verified.•The effect of air core on velocity field was studied.•The small apex/ vortex ratio possessed better product quality.