Enhancement of pollutants hydrocyclone separation by adjusting back pressure ratio and pressure drop ratio

To solve the long-term restrictions on the development of hydrocyclones (i.e., underflow diameter is difficult to flexibly and stably control, and underflow orifice and pipe are easy to be blocked), in 2017, researchers enhanced the hydrocyclone separation by using the underflow pumping to adjust the back pressure ratio, namely, ratio of the absolute underflow pressure to absolute overflow pressure. However, the effect of back pressure ratio may be affected by overflow pressure, whereas the pressure drop ratio, i.e., ratio of overflow pressure drop (pressure difference between inlet and vortex-finder outlet) to underflow pressure drop (pressure difference between inlet and underflow orifice), may be more reliable for monitoring the hydrocyclone-separation performance. Therefore, in this study, Discrete Phase Model and low-Re stress-omega Reynolds Stress Model, with which the near-wall sub-layer can be resolved, were employed to numerically and comprehensively compare their effects on the hydrocyclone-separation performance. Results indicate that, compared with back pressure ratio, pressure drop ratio is a more reliable parameter monitoring the hydrocyclone-separation performance. The reason is that, unlike the back pressure ratio, the effect of pressure drop ratio is basically not affected by the increase of overflow pressure. The optimum pressure drop ratio of the simulated hydrocyclone is within 119.3-135.3%. Because only at this time, the high separation efficiency (86.25-98.96%), small split ratio (0-46.07%), and the low total static pressure loss (2569.83-2951.58 Pa) can be simultaneously obtained. With increase of the pressure drop ratio, the split ratio linearly decreases, whereas the total static pressure drop decreases slower in general. This is consistent with the experimental results obtained by other researchers. The pressure drop ratio is proportional to the self-rotation speed of inertia-free particles in upper part of the hydrocyclone, whereas is inversely proportional to that in lower part of the hydrocyclone, especially that near the apex.