Chemical Engineering Science, Vol.157, 182-199, 2017
Influences of gas-liquid interface contamination on bubble motions, bubble wakes, and instantaneous mass transfer
To improve the efficiency of industrial processes and to precisely comprehend the complex mechanism of global warming, a thorough understanding of the mass transfer mechanism from a bubble to the surrounding liquid is essential. Here we investigated a single CO2 bubble (2.9 mm in equivalent dia.) that ascended in a zigzag motion in purified water and in water contaminated with a very small amount of 1-pentanol. We used a laser-induced fluorescence (LIF) technique and 8-hydroxypyrene-1,3,6-trisulfonic acid (HPTS), and we employed a pH-sensitive dye that was calibrated by means of a photoelectric optical fiber probe to visualize the bubble-to-liquid-phase mass transfer and the bubble's wake structure. Two high-speed cameras were used to capture the bubble wake (including the CO2 dissolution), the bubble motion, and the bubble wake from two orthogonal directions. Based on the visualization results, we obtained the volume, surface area, velocity, orientation angle and shape of the bubble from moment to moment. The instantaneous mass transfer coefficient of the bubble was precisely calculated from the above results. Due to reiteration of the adsorption and desorption of the surfactant on the bubble surface, the direction of the Marangoni convection was very difficult to identify. Here, based on our analysis of forces that were calculated from the bubble motion, we considered the direction of action of the Marangoni convection indirectly. On the basis of these experimental results, we discuss the influences of the bubble-surface contamination on the bubble motion and the mass transfer, as well as the bubble wake. (C) 2016 Published by Elsevier Ltd.