Characterizing Gas Phase Distribution in Slug and Churn Flows Using a Distributed Dual-Fiber Optical Probe

Intermittent flow patterns are commonly observed in gas-liquid two-phase flow systems, often exhibiting strong instability and heterogeneity. The accurate measurement of chord length distribution is a crucial step in further characterizing complex flow behaviors. In this study, the fiber optical probe with a tapered cone is designed to ensure efficient light energy reception, thus achieving a high measurement sensitivity. The experiments employ a distributed dual-fiber optical probe (DFOP) system, composed of eight DFOPs, in conjunction with high-speed imaging techniques. High-resolution measurements are conducted in a 20-mm inner diameter pipe, focusing on the bubble dynamic characteristics in both slug flow and churn flow patterns. The results indicate that in the slug flow, the bubbles are larger and symmetrically distributed around the center of the pipe. In contrast, in the churn flow, highly deformed bubbles are displaced from the center, with the maximum chord length occurring at the second ring position. This study demonstrates that the DFOP can precisely measure the gas-phase distribution characteristics in complex gas-liquid two-phase flows, providing essential insights into the understanding of intricate flow structures and offering significant implications for subsequent sensor optimization and measurements.