Computational investigation of the mechanisms of particle separation and “fish‐hook” phenomenon in hydrocyclones

Abstract

The motion of solid particles and the ''fish-hook'' phenomenon in an industrial classifying hydrocyclone of body diameter 355 mm is studied by a computational fluid dynamics model. In the model, the turbulent flow of gas and liquid is modeled using the Reynolds Stress Model, and the interface between the liquid and air core is modeled using the volume of fluid multiphase model. The outcomes are then applied in the simulation of particle flow described by the stochastic Lagrangian model. The results are analyzed in terms of velocity and force field in the cyclone. It is shown that the pressure gradient force plays an important role in particle separation, and it balances the centrifugal force on particles in the radial direction in hydrocyclones. As particle size decreases, the effect of drag force whose direction varies increases sharply. As a result, particles have an apparent fluctuating velocity. Some particles pass the locus of zero vertical velocity (LZVV) and join the upward flow and have a certain moving orbit. The moving orbit of particles in the upward flow becomes wider as their size decreases. When the size is below a critical value, the moving orbit is even beyond the LZVV. Some fine particles would recircuit between the downward and upward flows, resulting in a relatively high separation efficiency and the ''fish-hook'' effect. Numerical experiments were also extended to study the effects of cyclone size and liquid viscosity. The results suggest that the mechanisms identified are valid, although they are quantitatively different.

Fish hook effect in centrifugal classifiers – a further analysis

“…• They have neither observed nor reported fish hooks in any of their simulation results except in the study where the focus was exclusively on fish hook (Wang and Yu, 2010).…”

“…The effects of viscosity of the fluid and the cyclone size on the efficiency curve were investigated by Wang and Yu (2010). The results of simulation showing fish hook are shown in Fig.…”

“…The most comprehensive CFD simulation study and also the first and the only investigation focused exclusively on the fish hook effect in hydrocyclone classifiers is due to Wang and Yu (2010). In fact, Yu and co-workers, have been most active in CFD simulations on hydrocyclones (for example, Wang andYu, 2006, 2008;Wang, 2009;Wang and Yu, 2010;Ghodrat et al, 2012;Kuang et al, 2012 etc.…”

“…In fact, Yu and co-workers, have been most active in CFD simulations on hydrocyclones (for example, Wang andYu, 2006, 2008;Wang, 2009;Wang and Yu, 2010;Ghodrat et al, 2012;Kuang et al, 2012 etc. ) in recent times.…”

“…Ghodrat et al (2012) carried out CFD simulations with the same model as Kuang et al (2012). Wang and Yu (, 2010) mention that to validate their model, they compared the experimental data (Hseih, 1988) with simulation results for the performance characteristics of the hydrocyclone, namely, the pressure drop; volume split ratio and separation efficiency also.…”