On the estimation of the gas-side mass-transfer coefficient during the formation and ascension of bubbles

Abstract

Abstract Using a recently developed model for the simultaneous heat and multicomponent mass transfer during the formation and ascension of superheated bubbles, concentration profiles within a bubble during the stripping of diluted ethyl acetate solutions were determined and then used in the computation of the corresponding mass-transfer coefficient on the gas side, k G . Both isothermal and non-isothermal bubbling cases were analysed. For the studied system, the importance of the gas-side resistance to mass transfer was clearly shown. During the formation stage, a large drop in k G with time was observed, as the mean gas velocity inside the bubble decreased on account of bubble growth. On the other hand, after bubble detachment, the value of k G remained approximately constant throughout the ascension time. For isothermal bubbling, it was demonstrated that the decomposition of the bubbling process into formation and ascension stages with two different constant mean k G values is a sound approach because their usage in a much simpler mass transfer model did not lead to significant errors in the prediction of the final ester concentration in the bubble. In the case of non-isothermal bubbling, an increase of almost 300 K in the gas inlet temperature had little effect on the k G values for both stages.