Journal of Chemical Engineering of Japan, Vol.48, No.6, 418-426, 2015
Dissolution of Single Carbon Dioxide Bubbles in a Vertical Pipe
Dissolution of a carbon dioxide (CO2) bubble in the downward flow of water or glycerol-water solutions in a vertical pipe is measured by using an image processing method. Numerical predictions of bubble dissolution using a Sherwood number Sh correlation for a bubble in stagnant water, which was proposed in our previous study, are also carried out to examine its applicability to single bubbles in several fluid property systems. The correlation can predict the bubble dissolution well, during which large bubbles change from Taylor to small bubbles, not only in water but also in glycerol-water solutions. A small bubble in a 50 wt% solution predicted by using the correlation, however, dissolves slightly faster than the experiments in the diameter range of 5-8 mm. CO2 concentration fields visualized by using laser-induced fluorescence show that this is due to the difference in wake structures in the stagnant liquid and in the downward flow, that is, vortex shedding with shape oscillation in the stagnant liquid enhances mass transfer from small bubbles; whereas the closed wake in the downward flow reduces the mass transfer rate. This, in turn, implies that the Sh correlation can give good predictions for long-term bubble dissolution in various stagnant liquids.