Asymmetric Deformation of Bubble Shape: Cause or Effect of Vortex-Shedding?

0428014 - ÚCHP 2015 RIV SK eng J - Journal Article
Wichterle, K. - Večeř, M. - Růžička, Marek
Asymmetric Deformation of Bubble Shape: Cause or Effect of Vortex-Shedding?
Chemical Papers. Roč. 68, č. 1 (2014), s. 74-79. ISSN 0366-6352
R&D Projects: GA ČR GA104/07/1110
Grant - others:GA MŠMT(CZ) CZ.1.05/2.1.00/03.0082
Institutional support: RVO:67985858
Keywords : bubble * bubble shape * bubble velocity
Subject RIV: CI - Industrial Chemistry, Chemical Engineering
Impact factor: 1.468, year: 2014

Two perpendicular projections of rising bubbles were observed in counter-current downstream diverging flow. Evidently, the bubbles did not enter the boundary layer at the channel wall and a plug liquid flow assumption was acceptable in our experimental equipment. This confirmed that the experiment was appropriate for simulation of bubble rises in a quiescent liquid column. Recent data obtained by a high-speed camera permitted recording over a period of 60 s. Image analysis by a tailor-made program provided a time-series of quantities related to the position, size, and shape of bubbles. In addition to determination of the aspect ratio of the equivalent oblate ellipsoid, deviation from this shape was investigated in respect of the difference between the bubble's centre of mass and the geometrical centre of bubble projection. Autocorrelation of the data indicated that the bubble inclination oscillated harmonically with a frequency of 5-10 Hz; cross correlation showed that the horizontal shift of the centre of mass, as well as the horizontal velocity, increased with increasing bubble inclination, and the vertical shift of the centre of mass increased with an increases in the absolute value of the bubble inclination. There is no significant phase shift in the oscillation of these quantities. The bulky bottom side of the bubbles is in accordance with the model of bubble oscillation induced by instability of the equilibrium of gravity and surface tension forces. The oscillation frequency dependence on surface forces (Eotvos number) is evident, while viscosity does not play a significant role in low-viscosity liquids. Therefore, vortex-shedding is more likely to be an effect of the oscillation and not its cause.
Permanent Link: http://hdl.handle.net/11104/0233423