The effect of liquid viscosity and modeling of mass transfer in gas–liquid slug flow in a rectangular microchannel

Both chemical (by adding 0.05 M NaOH) and physical absorption of CO 2 into aqueous glycerol solutions with viscosity up to 45.6 mPa·s in a microchannel are investigated. The concentration distribution pattern, absorption time, and mass transfer coefficient are analyzed and discussed. A new concentration distribution pattern is observed with the lowest concentration locating at the channel center. It is shown for the first time that k L / D CO 2 0.5 presents a positive relationship with liquid viscosity, which is explained by the essential role of the mass exchange between the liquid film and bulk liquid slug. This mass exchange may lead to a rise in k L when increasing the liquid viscosity under some cases in chemical absorption. A mass transfer model is successfully applied to predict the bubble size evolution in physical absorption. The model also shows about 10–46% of the mass transfer contribution from liquid films before saturation.