Flow Visualization in Bubbly Two-Phase Hydraulic Jump

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Abstract
The present study investigates bubbly two-phase flow in a hydraulic jump using a flow visualization technique. Bubbly two-phase flow is encountered in many engineering problems; however, mainly because of experimental difficulties, little is known on the internal structure of these flows, although such knowledge is clearly essential to a thorough understanding of the mass transfer between the two component phases. In the past, some authors measured the distribution of void ratio in a hydraulic jump using hot-film anemometry. Nowadays this interesting technique may be improved using a flow visualization technique, which enables one to obtain the percentage of air across each vertical section of the jump. This is possible by evaluating the gray levels of the first principal axes of transformed images starting from RGB images. The experiments considered the phenomenon of air concentration in a hydraulic jump, which was studied and analyzed using image processing techniques, aimed at obtaining reliable quantitative measurements. To achieve this, the processing system was planned and tested at the hardware level and a procedure for managing the processing was set up. The calibration curve was obtained using the McCorquodale and Khalifa law (1983). The results permit the visualization of flow structures and the estimation of air concentration of the flow along all the jump and to show the position in which the air concentration reaches the maximum value versus time.

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