CFD simulations of liquid side local mass transfer characteristics and enhancement in capillaries under Taylor flow

The characteristics of liquid side mass transfer under Taylor flow in capillaries were studied by performing computational fluid dynamics(CFD) simulations.The local mass transfer coefficients on bubble surface were evaluated,and the effects of bubble rise velocity,length of liquid film and slug length on the mean mass transfer coefficients of liquid film and the two caps were investigated.Three peak values of local mass transfer coefficient were found on bubble surface.The average mass transfer coefficient of liquid film increases with the increase of bubble rise velocity and decrease of liquid film length,whereas the average mass transfer coefficient of the two caps varies less.Mass transfer coefficient in liquid film decreases as the film contact time increases,while that in the caps changes less.Moreover,the principle of field synergy was used to explain the characteristics and enhancement of local mass transfer.The coordination between the velocity and concentration fields was better near the liquid film and two bubble caps.The results show that short film contact time for the same contact area could enhance the gas-liquid mass transfer under Taylor flow.Finally,empirical correlations were proposed to predict the liquid side volumetric mass transfer coefficients for short and long film contact time separately,and the predicted values in capillaries with diameters of 0.25—3 mm have a relative error within ±20%.