Optical shadowgraphy analysis of gas bubble equivalent diameters: Factors influencing measurement accuracy in bubble flows

The article explores the impact of various factors on the determination of gas bubble equivalent diameters using optical shadowgraphy. The experimental setup involves a liquid-gas system. The results indicate that the distance between the camera and the bubble rise-up plane has negligible influence on measurement precision as long as the area captured is constant. Increasing the number of analyzed frames significantly reduces uncertainties, while higher image magnification leads to increased uncertainties due to a reduced number of frames and smaller area captured. Image distortion correction minimally affects results and precision. The study concludes that factors such as resolution, frame rate, and elongated flow path captured contribute to more accurate determination of equivalent bubble diameters, essential for the determination of mass and heat transfer coefficients in liquid-gas flows. The results indicate that a sufficiently high number of video frames may be more important than indiscriminately increasing the resolution.