Releasing a buoyant bubble stuck in a capillary tube

Type : Master’s project

Description : 

Long bubbles in vertical tubes of small diameter rise under the effect of gravity, provided the radius of the tube is larger than a critical value depending on gravity and on the surface tension of the surrounding fluid. For tube diameters larger than this critical value, Bretherton [1] could predict the rising speed of the bubble.

In this project, mostly experimental, we want to explore two different ways to allow for bubble motion into a wider range of tube diameters, namely for thinner capillaries.

Figure 1: Long bubble in a capillary tube (a) held vertically, (b) held vertically while rotated around its central axis, (c) tilted with respect to the vertical axis. A bubble initially stuck in a very thin capillary tube (a) could be released if centrifugated (b), or if the axisymmetry is broken (c).

Scope : 

The first part aims at investigating the effect of centrifugal forces when the vertical tube is rotated around its axis, Figure 1 (b). More precisely, an already existing experimental set-up will be used to characterize the blockage conditions for different angular velocities and various tube radii and to measure the speed of the bubble, so as to compare the resulting experimental data with theoretical curves relating the speed of the bubble and the rotational speed.

The second part, that can be implemented in parallel of the first one, consists in designing an experimental set-up aiming at investigating the effect of the axisymmetry breaking that occurs when the tube is tilted with respect to the vertical axis, Figure 1 (c). Here, the blockage conditions and the rising speed of the bubble will be measured as a function of the tilt angle, and compared to theoretical predictions.

Supervisors : Alice Marcotte & François Gallaire

[1] Bretherton, F. P. 1961 The motion of long bubbles in tubes. J. Fluid Mech. 10 (02), 166-188.