Visualization and characterization of gas–liquid mass transfer around a Taylor bubble right after the formation stage in microreactors

• Visualization of mass transfer around Taylor bubbles in microreactor.
• Contributions of the bubble formation stage to the overall gas–liquid mass transfer.
• The enhancement by the recirculation in the gas bubble at the formation stage was studied.
• New insight into bubble mass transfer right after the formation stage.
• Basis for elaborating a complete model, accounting for the bubble formation stage.

The gas–liquid mass transfer occurring in Taylor flows right after the bubble formation stage were investigated in a flow-focusing microreactor. The colorimetric technique proposed by Dietrich et al. (2013) was used for locally visualizing and characterizing the gas–liquid mass transfer. Thanks to this method, the liquid-side mass transfer coefficients kL were measured at the moment right after the bubble is detaching from the gas film near the cross-junction of the microreactor. Experiments were carried out for several flow conditions (95.7