Investigation on the evolution of flow field stability in a spiral separator

Abstract

The liquid film in a spiral separator undergoes an evolution from unsteady to steady flow with increasing trough length. Understanding the process of the flow field evolution is a prerequisite for revealing the mechanism of particle segregation. In this study, a numerical investigation of the flow field evolution in a spiral separator with the cross-sectional profile of cubic parabola is conducted. The distribution profiles of the liquid film thickness, surface tangential velocity, and net radial flux along the trough length are used to characterize the stability of the liquid film shape, primary flow, and secondary flow, respectively. The results indicate that the flow field characteristics at the inner and middle troughs will reach a stable state earlier than that of the outer trough with the increase in trough length. Before reaching a fully developed steady state, the instability of the flow field characteristics at the outer trough exhibits damped oscillations. The instability of the flow field in the first turn is mainly caused by the collision between the fluid and the outer trough sidewall, which leads to large fluctuations in the flow field characteristics at the outer trough. Moreover, the unbalanced inward and outward flows generated from the collision may be the primary reason for the formation of the secondary flow. After the first turn, the flow field characteristics have approximately stabilized, but a certain transitional trough length is still required to reach a fully developed steady state. The secondary flow shows poorer stability compared with the liquid film shape and primary flow. These observations provide insight into the physics of the fluid flow in a spiral separator.