Experimental study on flow patterns and transition criteria for vertical swirling gas-liquid flow

Swirling gas-liquid flow has a wide variety of engineering applications in petroleum, chemical, and nuclear industries. A fundamental understanding of swirling flow patterns and their transitions is essential for the proper modelling of pressure drop, mass transfer rate and interfacial area in swirling two-phase flow. Although the gas-liquid flows in straight pipes have been widely studied, little attention has been paid to characteristics at transition boundary of swirling gas-liquid flow. In this paper, based on high-speed camera method using back light source, flow patterns and transition criteria for swirling gas-liquid flow induced by a vane-type swirler were experimentally investigated in a vertical tube of 30mm I.D., operating at ambient temperature and pressure. According to our observation, five typical flow patterns, i.e. swirling gas column flow, swirling intermittent flow, swirling annular flow, slug flow and churn flow, were identified and the detailed characteristics at the transition boundaries were discussed with flow-regime reconstruction technique. The spatial and temporal evolution of the gas core diameter in swirling flow regimes were also analyzed using image processing technique. Additionally, the flow-regime transition criteria were gained which reveal that the void fraction alpha(g) in swirling gas column flow is below 0.3 similar to 0.32 and it attains values of 0.32 to 0.71 in the swirling intermittent flow. When alpha(g) is greater than 0.71 similar to 0.74, the swirling intermittent flow transforms into swirling annular flow. (C) 2019 Elsevier Ltd. All rights reserved.