Rising Velocity of a Gas Plug in Vertical-Rectangular-Narrow Channels

Bubble rising velocity in stagnant water in rectangular channels was examined. The width of the flow channels and the gap space between parallel walls were varied from 10 mm through 150 mm and from 1 mm through 10 mm, respectively. When the bubble had plug shape in the long side and also the short side, the bubble velocity took the same velocity as that in a circular pipe that had the same periphery. When the bubble lost the plug shape in the long side, the rising velocity became fast as the long side shape departed from the plug shape. When the long side was large enough for the bubble to have the shape of a bubble in open space, the bubble rising velocity was expressed well with the expression for the bubble rising velocity in open space. As the long side became narrow, the bubble rising velocity became slower than that for open space. When the gap spacing was quite narrow; 1 mm, and the long side was less than 15 mm, the bubble stopped rising halfway in the flow channel. When the bubble took the shape of a plug, the bubble rising velocity did not depend on the film thickness between the bubble and the long-side wall in the present experimental range.