Measuring Bubble Shapes in the Long Straight Rectangular Pipe under Different Flow Conditions

Experiments of air-water flows were conducted in a long straight rectangular pipe with the longitudinal length L=10 m to investigate the air-water flow properties including bubble shapes and bubble distributions for a varied range of discharges in cross-sections of different locations. The present investigation in hydraulic engineering mostly focused on the air concentration. Though some researchers noticed the importance of the size and shape for every single bubble in bubbly flows, solely relying on the measurement of the conductivity probe could only get the chord length of the assuming equivalent sphere of the bubble. From the observation of experiments, the spherical hypothesis was not accurate enough and some important parameters like the aspect ratio of the bubble were missing. Therefore, the high-speed camera and image processing techniques were applied in this paper to get more precise information of the bubble under different discharges. Additionally, to get rid of the mutual interference and overlap of the bubbles, the syringe pump that is capable of accurately controlling gas flow was used to generate a succession of disperse bubbles. Improved understanding is gained through the investigation, which reveals the major parameters of the bubble and the development of the bubble along the flow direction.