Rocking motion, trajectory and shape of bubbles rising in small diameter pipes

The trajectory, rocking motion, and shape of a single air bubble rising in water were investigated utilizing the particle tracking velocimetry (PTV) m easurement technique. The three components of the velocity and acceleration vectors of the bubble were obtained by employing a stereoscopic technique. This technique allowed for a better description of rising bubble behavior. Four charged coupled device (CCD) cameras at different view angles acquire d the view volume images. Two experimental configurations were employed in this study. In the first setup the bubbles were tracked for a duration of 1 33.3 ms. The viewing area was 24.6 mm high and 18.6 mm wide, so the bubbles trajectories could be determined. In this configuration, the bubbles rose in a stagnant and a laminar water flow. The average equivalent spherical di ameter of the bubbles was 3.6 mm. In the second experimental setup configur ation, the bubbles were tracked for 66.7 ms, but the viewing area was reduc ed to 11.0 mm high and 13.0 mm wide. In addition, a combined shadow particl e image velocimetry (SPIV) technique was employed. This technique allowed f or an accurate description of the bubble shape. The results indicate that t he trajectory of the bubbles was zigzag or helical, and the shape was oblat e spheroidal. The period of the cyclic motion and the amplitude decreased a s a result of the wall effect. The bubbles rising close to the pipe wall ha ve more rotational behavior than the bubbles flowing through the pipe cente r. This is a consequence of bubble/wall interaction. (C) 2001 Elsevier Scie nce Inc. All rights reserved.