Experimental study of the effect of pipe size on bubbly to beyond-bubbly flow regime transition

Abstract

The two-phase flow regime and its transition is closely related to the flow channel geometry. In this study, the effect of pipe size on the bubbly-to-beyond-bubbly flow regime transition was experimentally investigated. Experiments focusing on air-water two-phase bubbly to slug flow regime transition using impedance meter and high-speed imaging were performed on 12.7 mm, 25.4 mm, and 50.8 mm inner-diameter vertical upward pipes. The flow conditions were finely selected and cover a range of superficial liquid and gas velocities of <jf> = 0.3–2.0 m/s and <jg> = 0.03–2.5 m/s. The flow regime identification was realized using a 1-D convolutional neural network-based learning algorithm, with the aid of 5 different data augmentation methods. Through the experimental results, the difference of the transition boundary between bubbly to cap-bubbly/slug flow among different pipes sizes was observed. The difference among the pipes is due to the pipe wall effect on the bubble distribution and relative motion. For a smaller diameter pipe, the transition happens in a smaller void fraction. A simple flow regime transition criterion is proposed regarding the wall effect based on Mishima-Ishii’s approach.