Visualization and image measurement of buoyant bubbly flow through circular cylinders arranged in a narrow channel

Bubble-driven flow around circular cylinders in a narrow channel is experimentally investigated by means of image processing. The cylinders are settled in the channel with three kinds of arrangement pattern to clarify the difference of the internal two-phase flow structure. Thinning algorithm is applied to the detection of all the bubbles in order to measure the bubble motion in locally high void fraction. Size and spatial distribution of the bubbles are also obtained with the image analysis to discuss the bubble's coalescence/fragmentation due to the collision with the cylinders. The results imply that the rising velocity of the bubble is governed not only by bouncing on the cylinders but also by the liquid phase flow pattern that is sensitively dependent on the gas flow rate and the cylinders' arrangement pattern. (author)