Recovery Vanes Research Articles

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

AbstractThe separation of gas and liquid is a topic of general interest in science and engineering, for which tremendous efforts are endeavored to develop separators with high efficiency and reliability. However, when it comes to ultralow gas content, some of the separators fail. A special separator finds the potential herein, which consists of a swirl vane, a swirl chamber and a recovery vane. When the gas–liquid mixture goes through the swirl vane, bubbles will be concentrated into the swirl chamber center and evolved into a gas core. However, two key issues need to be addressed for the axial separator before industrial applications. One issue is that all the bubbles must be captured without exception, that is, the separation efficiency is close to 100%. The other issue is the stability of the gas core, the shape of which is sometimes rectilinear and sometimes spiral. A successful separation relies on the rectilinear shaped gas core. Focused on the two issues above, tremendous experimental, numerical and theoretical investigations have been carried out. In this article, the key challenges and solutions for the two issues are summarized.

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 pressure 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 (PIV). 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.