Bubble Separation in a Gas–Liquid Swirling Pipe Flow

Gas–liquid swirling pipe flow plays an essential role in phase separators. Bubble motions and flow patterns transitions in the flow are crucial for further investigation of this flow. However, much attention has been paid to these in non-swirl flow instead of swirl flow. In this work, bubble separation generated by a vane-typed swirler in a vertical pipe with an inner diameter of 62 mm was experimentally studied. Superficial air velocities (0.036 − 1.41 m/s) and superficial water velocities (0.02 − 0.95 m/s). The results show that dispersed bubbles gradually transform to gas column flow with increasing superficial water velocities (0.093 − 0.640 m/s) in the swirl flow; gas column flow gradually transforms to swirling intermittent flow with increasing superficial air velocities (0.05 − 0.40 m/s), and one peak increases to two peaks in the probability density function curve of pressure drop; slug flow can transform to swirling intermittent flow. Finally, transition criteria for bubble separation were proposed: when the turbulent fluctuations are strong enough to overcome centrifugal force, then the bubbles move to the pipe center and coalescence with each other, lead to the transition of gas column flow/swirling intermittent flow.