Experimental Studies of Convective Self-Oscillations near the Lateral Surface of a Bubble in Plane Rectangular Channel
- Paper number
IAC-06-A2.4.03
- Author
Prof. Dr. Antonio Viviani, Seconda Universita di Napoli, Italy
- Coauthor
Andrey L. Zuev, Russia
- Coauthor
Mr. Konstantin G. Kostarev, Russia
- Coauthor
Prof. Antonio Viviani, Seconda Universita di Napoli, Italy
- Year
2006
- Abstract
The paper presents the results of the experimental exploring in terrestrial conditions a specific oscillatory regimes of the solutocapillary Marangoni convection, arising around a stationary air bubble in an aqueous solution of the surfactant with a vertical concentration gradient. The new experiments were performed with a view to visualize the structure of the convective flows, to trace the evolution of concentration fields and to explain the physical mechanisms for the periodic intensification of convective mass transfer around the bubble. The test object represented an elongated rectangular horizontal channel, 2 mm high and 1.2 mm thick, confined between two vertical glass plates. The channel was filled with vertically stratified solution of methyl, ethyl or isopropyl alcohol and was blocked at one end by the bubble lateral surface. Due to a small channel thickness the arising convective flow and distribution of the surfactant concentration were nearly two-dimensional which makes it possible to investigate them using interferometric technique and to compare the experimental results with numerical calculations made for rectangular area. The experiment revealed the interaction between two types of convective motion: the short-term intensive solutocapillary Marangoni convection near the bubble and the relatively slow large-scale gravity-induced flow in the fluid bulk. The first flow had the form of a localized vortex in which the surfactant under the action of solutocapillary forces moved along the surface of the bubble toward its lower pole. The vortex rapidly stirred the solution stratification near the bubble which eventually created a thin fluid layer with homogeneous concentration around the bubble free surface. This caused a decay of the Marangoni motion and formed in the channel a horizontal concentration gradient initiating in the fluid an advective buoyancy flow, which restored the disturbed distribution of concentration and drew more surfactant from the solution towards the bubble surface. As soon as this happened the whole cycle of oscillations restarted. The time dependences of the oscillations period are analyzed in relation to the average concentration of the solution, the concentration gradient and the diffusive Marangoni and Grashoff numbers.
- Abstract document
- Manuscript document
IAC-06-A2.4.03.pdf (🔒 authorized access only).
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