Abstract
Upward flows of air-water two-phase mixture formed in 24mm and 64mm dia., long vertical pipes were observed to obtain further knowledge of development process from a bubbly flow to a slugflow. The vertical pipes had 13m length in height and were made of transparent acrylic resin. Ascending motions of the air bubbles in the pipe were tracked by a CCD camera, which was able to move along the vertical pipe. Flow pattern maps were described on a z-jG plane, here z is a height measured from thebottom of the pipe and jG is a superficial air velocity. Bubbly flows including bubble clusters wereobserved in both 24mm and 64mm pipes. However, slug formation processes were much different between 24mm and 64mm pipes, even if the air entrance conditions were same. By coalescence of bubbles in the 24mm pipe, large Taylor type bubbles were formed from the bubble clusters. However, thebubble clusters in the 64mm pipe did not grow up directly to the Taylor type bubbles. They grew up to large bubbles when the relatively large cap type bubbles were formed from the air nozzle set at the bottom of the pipe.
