Dissolution of single carbon dioxide (CO2) bubbles in a vertical pipe of 25 mm in diameter are measured to examine the effects of the ratio λ of sphere–volume equivalent bubble diameter d to pipe diameter D, liquid Reynolds number ReL and surfactants on mass transfer. The bubble diameter d and Reynolds number ReL are varied from 5.0 to 26 mm (λ = 0.20 − 1.0) and from 0 to 3100, respectively. Millipore water, tap water and water contaminated with Triton X–100 are used for the liquid phase. Mass transfer coefficients kL are evaluated from changes in d. The kL decreases with increasing λ for bubbles in stagnant millipore water because of the decrease in bubble rising velocity due to the wall effect. Measured Sherwood numbers Sh do not depend on ReL because a turbulent fluctuation velocity in bulk liquid flow is much smaller than a relative velocity between a bubble and liquid. The mass transfer correlation for a bubble in a stagnant liquid proposed by Johnson et al. is applicable to a bubble in pipe flow, provided that a correct relative velocity between a bubble and liquid is substituted in the correlation. Due to the retardation of capillary wave, mass transfer coefficients for bubbles in contaminated water becomes smaller than those in millipore and tap waters.

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