2146 チャネル内気泡流乱流の LDV・PIV 計測  [in Japanese] LDV/PIV Measurements of Turbulent Bubbly Flow in a Vertical Channel  [in Japanese]

Measurements of the turbulent properties and local void fraction distribution for bubbly channel flow are reported. Liquid phase velocities and local void fraction are measured using Laser Doppler Velocimetry (LDV) and Image Processing respectively. In bubbly flow, addition of a small amount of 3-pentanol behaving as surfactant changes its flow structure drastically. Absorption of surfactants on the bubble surface prevents bubble coalescence and keeps bubbles smalland mono-disparsed size. So we used two types of bubbles selectively, one has mono-dispersed 1mm diameter under the condition of "with 3-pentanol" and the other has wide spread 1-4mm diameter under the condition of "without 3-pentanol". It is shown that depending on their diameter, tendency of bubble migration toward the wall varies. This tendency links to a deformation of bubble. In the case of "with 3-pentanol", bubbles highly accumulate in the vicinity of the wall. Then the features of bubbly channel flow such as steeper velocity gradient near the wall and flattened turbulent properties in the center of the channel become increasingly prominent.