An experimental investigation was conducted with a high-speed camera to explore the hydrodynamics characteristics of slug flow in a microchannel with a cross-section of 1 mm×1 mm. Pure carbon dioxide and water were used as working fluids. The influence of superficial gas and liquid velocities and the wettability of microchannel on the two-phase flow pattern and mass transfer was investigated. In the hydrophilic microchannel

bubbly flow

bubbly-slug flow and slug flow were observed. In the hydrophobic microchannel

asymmetric slug flow

elongated asymmetric slug flow

stratified flow were found. It was shown that in slug flow of the hydrophilic microchannel

the length of bubble increased generally with the increase of superficial gas velocities and the decrease of superficial liquid velocities. The length of liquid slug decreased generally with the increase of superficial gas velocities

and increased firstly and then decreased generally with the increase of superficial liquid velocities. As the improvement of superficial gas and liquid velocities

the liquid volumetric mass transfer coefficient kLa increased. The liquid volumetric mass transfer coefficient kLa in the hydrophilic microchannel was higher than that in the hydrophobic microchannel.