A robust image analysis technique for the study of horizontal air-water plug flow

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The current work develops a robust image analysis technique for quantitative measurements in horizontal plug flow. To do this, experiments are performed to capture high-speed videos for horizontal air-water plug flow for two test conditions in a 38.1 mm ID pipe. A visualization block-mirror system is designed and fabricated to allow the simultaneous visualization of two-phase flow from both top and side views using a single camera. To obtain images of high quality for analysis, the angle and position of the camera relative to the visualization block are verified. With the obtained images, an algorithm is developed to detect and track the interface of plug bubbles. Due to the existence of contacting or overlapping small bubbles, additional algorithms are developed to segment the interfaces of plug bubble from those of small bubbles, including distance checking, interface breakpoints detection, and convex curvature segmentation. As a result, the nose position, local time-averaged axial velocity, and area-averaged time-averaged void fraction for plug bubbles can be obtained with this newly developed image analysis technique. To benchmark the newly developed image analysis code, local four-sensor conductivity probe measurements are performed. The axial velocity for plug bubbles generally agrees within ±10% between image analysis technique and the four-sensor conductivity probe measurement technique, while the plug bubble reconstruction approach can generate an area-averaged void fraction within ±10% of the probe measured value.