Investigation of Elongated Bubble Centring in Slug Flow Based on Image Processing

The intermittent slug flow in horizontal circular pipes occurs commonly in industrial applications such as pipeline transportation and nuclear reactor cooling. The phenomenon of elongated bubble centring in slug flow can affect the bubble interface morphology, resulting in fluctuations of characteristic parameters. Therefore, it is important to acknowledge the extent to which bubble centring occurs and the possible influencing factors. This paper aims to investigate the elongated bubble centring in moderately sized pipes based on the laser-induced fluorescence method. A new image processing procedure is developed to measure the centring degree. A novel segmentation method is proposed to improve measurement accuracy by combining the global threshold algorithm with the Grey Wolf Optimization. The statistical analysis shows a positive correlation between the Froude number and the degree of bubble centring. Furthermore, the effect of superficial flow rate ratios is explored in the cases of similar Froude numbers. Finally, the results are verified by the models and the experimental data previously published.