Experimental investigations on rising bubbles in vertical capillaries

Abstract

We investigate how the walls of cylindrical capillaries affect the velocity of rising gas bubbles of various diameters. Of course, as the capillary diameter increases, the velocity of the rising bubble will approach the case of free rising. Such systematic experiments on bubble rise in capillaries, in which the ratio of bubble diameter and capillary diameter is varied from one towards smaller values, can hardly be found in literature. First orienting experiments within the system water/air have been conducted and will be discussed in this paper.

Experimental investigations on rising bubbles in stagnant water in vertical capillaries

“…Beyond the maxima of both curves, the influence of the wall effect becomes stronger, such that the rising velocity decreases as the bubble diameter increases. Both curves show the significant scatter of the data near the maxima, as already mentioned before in [1]. As already discussed in [1], Tomiyama [4] confirms the faster rise of deformed bubbles and suspects an effect of the initial deformation of the bubbles during the formation at the needle.…”

“…Both curves show the significant scatter of the data near the maxima, as already mentioned before in [1]. As already discussed in [1], Tomiyama [4] confirms the faster rise of deformed bubbles and suspects an effect of the initial deformation of the bubbles during the formation at the needle. Though, we cannot confirm this relationship in our experiments, we are able to confirm characteristic differences in the bubble formation, but these only depend on the bubble diameter.…”

“…Together with the averaged velocity, two graphs are obtained. As already discussed in [1], wall effects can be neglected for small bubble diameters and the rise of these small bubbles appears comparable to the rise in an infinitely-extended liquid. In contrast, for larger bubbles, the wall affects the rising velocity of the bubbles substantially.…”

“…The equivalent diameter d eq is the diameter of a sphere of equal volume. A schematic drawing and an explanation of the entire experimental setup can be found in [1]. After the bubble generation within a calibration capillary, the bubble is transported to a metal needle.…”

“…As the gas bubble then rises in the glass capillary, which is filled with stagnant water, the bubble passes through two laser light sheets and the rising velocity is determined by measuring the time difference between the passage of the gas bubble through these two laser sheets (cf. [1]).…”