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Investigation of air bubble motion in water through a vertical narrow rectangular channel by using image processing techniques

Özdemir, Sancak
This thesis presents the study of air bubble motion in stagnant water and in upward flowing water through a vertical narrow rectangular channel of 2.1X66.5 mm cross section by using image processing and analyzing techniques. The investigated bubble size range is 2 - 70 mm in area equivalent bubble diameter and mean water flow velocity is 0-25 cm/s. This study focuses on the quantitative assessment of bubble size (perimeter, area, volume, width and height), shape, path and rising velocity. The observed bubble shapes consist of circular, ellipse, ellipse wobbling, hat wobbling, cap-hat, cap and cap-bullet types. Ellipse wobbling and hat wobbling type bubble region show transition from ellipsoidal to circular cap region. The results of the ellipse bubble tests were compared with the rise velocity correlation of ellipsoidal bubbles in infinite medium and an empirical correlation for two dimensional ellipse bubbles was obtained. The cap bubble rise velocities measured in this study were compared with the correlations in literature and a new empirical correlation which is different from those given in the literature was obtained from the experimental results of this study. The trends of the cap bubble deformation which is defined as bubble height to bubble width ratio, for various water streams are almost similar in behavior. Therefore, a correlation was obtained from the measured cap bubble deformation values in water stream. The experimental results show that the bubble relative velocity under co-current flow conditions for area equivalent bubble diameter to channel width ratio, ?ae<0.6 is less than that under stagnant water condition. After bubble shapes reach to the slug type (?ae ? 0.6), relative bubble velocities pass over the terminal bubble velocities in stagnant water. If the water velocity is increased further, the bubble relative velocity increases in the slug