Profiles of local velocities of bubbles in n-butanol, n-hexanol and n-nonanol solutions

Local velocities, size and deformation of bubble were measured in distilled water and solutions of n-butanol, n-hexanol and n-nonanol as a function of distance from capillary at which the bubbles were formed. CCD camera and stroboscopic illumination were used for monitoring and video recording of the bubbles rising inside square glass column. Sequences of the recorded frames were digitized and analyzed using image analysis software. It was found that the bubbles were deformed immediately after departure from the capillary orifice. Degree of deformation (ratio of horizontal and vertical diameters) was the largest in clean water and dropped rapidly from 1.5 in distilled water to a level approximately 1.05-1.03 at n-alkanol solutions. At low concentrations of the solutions the profiles of the bubble local velocity showed maximum at distances approximately 5-50 nun from the capillary orifice, prior to reaching a value of the terminal velocity. Position, height and width of the maximum varied with solution concentration. No maximum was observed at distilled water and at high concentrations of n-butanol, n-hexanol and n-nonanol solutions. Degree of adsorption coverage at surface of the departing bubbles were calculated and the bubble velocities were analyzed in a function of the adsorption coverage at different concentrations of the solutions. (C) 2002 Published by Elsevier Science B.V.