Local investigations on the gas-liquid mass transfer around Taylor bubbles flowing in a meandering millimetric square channel

•Local investigations of the gas-liquid mass transfer in a meandering millichannel.•The presence of bends affects significantly the gas-liquid mass transfer.•Evolution of mass flux of O2 transferred along the channel length.•Influence of the connection part of two “straight” sections on mass transfer. Gas-liquid mass transfer around Taylor bubbles moving in a meandering millimetric square channel was locally visualized and characterized in the present study. For that, the colorimetric technique proposed by Dietrich et al. (2013) was implemented. With this technique, the evolution of equivalent oxygen concentration fields in the liquid slugs passing through one and several bends was firstly described. In particular, it was observed how the flow structure (recirculation zones) inside the liquid slugs were twisted and split by the periodic bends (centrifugal effect), until reaching, after several bends, a uniform O2 concentration inside the liquid slugs. The influence of the “turning point”, joining two “straight” sections of meandering channel was also highlighted: a slowing down of the gas-liquid mass transfer was clearly shown. Volumetric mass transfer coefficients were determined at last by fitting the experimental axial profiles of averaged oxygen concentrations in the liquid slugs (before the turning point) with the ones predicted by a classical plug-flow model.