The Effect of Inlet Velocity on the Separation Performance of a Two-Stage Hydrocyclone

Abstract

The “entrainment of coarse particles in overflow” and the “entrainment of fine particlesin underflow” are two inevitable phenomena in the hydrocyclone separation process, which canresult in a wide product size distribution that does not meet the requirement of a preciseclassification. Hence, this study proposed a two-stage (TS) hydrocyclone, and the effects of the inletvelocity on the TS hydrocyclone were investigated using computational fluid dynamics (CFD).More specifically, the influences of the first-stage inlet velocity on the second-stage swirling flowfield and the separation performance were studied. In addition, the particle size distribution of theproduct was analyzed. It was found that the first-stage overflow contained few coarse particlesabove 40 μm and that the second-stage underflow contained few fine particles. The second-stageunderflow was free of particles smaller than 10 μm and almost free of particles smaller than 20 μm.The underflow product contained few fine particles. Moreover, the median particle size of thesecond-stage overflow product was similar to that of the feed. Inspired by this observation, wepropose to recycle the second-stage overflow to the feed for re-classification and to use only thefirst-stage overflow and the second-stage underflow as products. In this way, fine particle productsfree of coarse particle entrainment, and coarse particle products free of fine particle entrainmentcan be obtained, achieving the goal of precise classification.

Editorial for the Special Issue: “Physical Separation and Enrichment”

“…Zhang et al [9,10] provide evidence for understanding the flow field distribution in hydrocyclones and the development of multi-product grading instruments in terms of both theory and industrial applications. Jiang et al [11] also discuss the effect of inlet velocity on the separation performance of a two-stage hydrocyclone. The entrainment of coarse particles in overflow, and fine particles in underflow, are two inevitable phenomena in the hydrocyclone separation process which can result in a wide product size distribution.…”

Particle Motion Characteristics in W-Shaped Hydrocyclones

“…The working characteristics of two different materials at distinct flow rates in this hydrocyclone were studied, and the model validity was verified via a comparison to experimental data. Jiang [26] used a two-fluid model (TFM) to conduct numerical simulations of a two-stage hydrocyclone and obtained its internal flow field distribution and particle classification performance. Patra [27] applied the CFD technique and a three-dimensional double-precision separation steady-state solution tool based on the Reynolds-averaged Navier-Stokes method to study the complex flow characteristics inside a hydrocyclone with a spiral rib and found that the total pressure drop of the hydrocyclone was smaller than that of a conventional one.…”

Effects of Wall Roughness on the Separation Performance of Hydrocyclones under Different Inlet Conditions

“…Ci et al and Zhou et al found that increasing wall roughness reduces the pressure drop but leads to an inferior collecting efficiency of particles, and hence, there must be a compromise condition between them for a specific application. In contrast, the Euler–Euler approach, also referring to the two-fluid model (TFM), considers a group of particles as interpenetrating continua and averages the properties over cells, which is more computationally efficient, especially for the cases involving small particles. , Based on this method, researchers have extensively studied the effects of structural ,− and operational − parameters as well as their interactions. − Nevertheless, the wall roughness effects on the separation behavior of a conventional classifying hydrocyclone are rarely reported. Moreover, most numerical studies prefer an equal flow rate condition at the inlet to improve the numerical stability, which is inconsistent with the equal pressure condition used in practice and may cause some misunderstandings …”