Flow visualization in bubbly two-phase hydraulic jump

The present study investigated the bubbly two-phase flow in hydraulic jump, using flow visualization technique. Bubbly two phase flow is encountered in many engineering problems; however, mainly because of experimental difficulties, little information is at present available 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 hydraulic jump using hot-film anemometry. Now this interesting technique may be improved using flow visualization technique, which enable to obtain the percentage of air in each pixel and across each vertical section of the jump. This is possible by evaluating the gray levels of the first principal axes transformed images starting from RGB images. The experiments considered the phenomenon of air concentration in hydraulic jump, which was studied and analysed using image processing techniques, with the aim of obtaining reliable quantitative measurements. To achieve this, the processing system was planned and tested at hardware level and a procedure for managing the processing on software was set up. The calibration curve was obtained using McCorquodale J.A. and Khalifa A. (1993) law. The results enable to evaluate air concentration of the flow along all the jump and to show the position in which the air concentration reaches the maximum value against time.