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