Computational analysis and optimization of hydrocyclone size tomitigate adverse effect of particle density

The interaction between particle density and cyclone size is crucial for selecting hydrocyclone size but not clearly understood. This paper presents a numerical study on the effect of particle density on the multiphase flows and performance of hydrocyclones with respect to cyclone size by the recently developed two-fluid model. The numerical results show that more ultrafine particles are misplaced to the underflow in smaller cyclones, which is pronounced for heavier particles. On the other hand, coarse light particles are more likely to unexpectedly report to the overflow in larger cyclones. Moreover, the handling of lighter particles gives rise to a decreased separation precision and an increased cut size. This result is consistent with the experimental observations and pronounced in large hydrocyclones. The inner flows and the forces acting on particles have been analysed in details. It is shown that the particle separation behaviors against particle density and cyclone size mainly attribute to two factors. One is the relative importance of the radial accelerations due to the centrifugal, pressure gradient and drag forces acting on particles, respectively. These accelerations collectively determine the radial motion of particles and thus their chance of entering the proper flow streams for separation. Another is the extent of particle accumulation near the spigot. Such accumulation reduces the separation space of hydrocyclone and blocks the ways of particles for separation, although it mitigates the water entrainment effect on ultrafine particles,to some extent. Based on the results from this study, a mid-range cyclone size is recommended to mitigate the adverse effect of particle density and obtain relatively precise particle separation on the condition that the expected cut size can be achieved.