Mass transfer coefficients, velocities and shapes of carbon dioxide bubbles in free rise through distilled water

Abstract

Novel experimental techniques were used to study the instantaneous dissolution rate of free rising single carbon dioxide bubbles in distilled water. The shape of the bubble was also recorded at the instant its solution rate was being measured. The shapes of carbon dioxide bubbles less than 1 cm in equivalent spherical diameter were in close agreement with published data while larger bubbles were less flattened than reported. The mass-transfer coefficients of bubbles in the size range 0·4< d e <3·1 cm were virtually independent of bubble age. Bubbles in the range 0·4< d e <1·9 cm dissolved with a constant transfer coefficient close to 0·028 cm/sec. Coefficients for bubbles less than 1 cm in size lay within 10 per cent of theory for oblate spheroids in potential flow. Bubbles between 1·4 and 2 cm in size were found to be highly deformed, and their transfer coefficients were consequently 20 per cent higher than predicted by an expression for spherical caps in potential flow. Spherical caps 2·4–2·8 cm in size dissolved with transfer coefficients close to theoretical spherical cap values, but coefficients for bubbles around 3 cm in diameter were 30 per cent above spherical cap theory.