Investigation on Swirl Instability in a Vane-Type Separator With Tomographic Particle Image Velocimetry

Abstract

The separation efficiency of a vane-type separator is greatly affected by swirl instability. The separator consists of a swirling vane, a recovery vane and a main pipe. Driven by centrifugal force, the bubbly flow tends to develop into stratified flow with a continuous gas core floating in the central axis of the separator and facilitating the separation. Yet, the straight gas core can turn into a double helix under some circumstances for example if the pressure difference across the orifices of recovery vane falls below the critical value, and swirl instability occurs. In order to reveal the underlying mechanism, a device with adjustable operating pres-sure was introduced to reproduce the dynamic process of gas core transform between stable and unstable. With the increase of pressure difference, the gas core morphology near the recovery vane will turn from double-helix to straight-line within several seconds. The whole process was investigated further by using the tomographic particle image velocimetry. Results show that the development of vorticity structures in the swirl flow gives rise to the evolution of gas core morphology and keeps it stable. Furthermore, the direction of axial velocity, which becomes negative by low pressure differences, is found to be crucial in controlling the formation of inner forced vortex and hence leading to the occurrence of swirl instability. In addition, the magnitude of positive axial velocity is identified to be of great significance in vorticity enhancement.

Review on key issues of an axial gas–liquid separator for ultralow gas content

“…Given the relatively low efficiency of two phase simulation, a simpli- F I G U R E 2 2 The variation of axial velocity profiles during the transition process 84…”

“…By intercepting its cross section indicated in Figure 22, it can be found that the swirl stability is related to the sign of the axial velocity near the recovery vanes, and the negative axial velocity causes the swirl instability. 84 The results in Figures 20 and 22 show that the axial velocity distribution at the center of the cross section changes from V-to W-shape when the air core transits from unstable to stable.…”