The hydrodynamic characterization of gas-liquid flow regimes and the qualitative mass transfer characterization with a colorimetric technique have been carried out through a straight millimetric square channel with a section of 2mm2, a total length of 1.03m and three bends. Firstly gas-liquid hydrodynamics has been characterized for a water/air system. The different hydrodynamic flow characteristics as a function of operating conditions have been studied. In particular, the influence of air injection point on the regularity of the flow, the boundary gas-liquid flow rates for the Taylor regime flow, the flow cartography, the bubble length, the bubble shape, the unit cell length, the bubble velocity, the bubble volume and the generation frequency have been investigated. All the results have been compared with the study carried out by Roudet et al. (2011) [1]. Secondly a qualitative analysis of mass transfer has been done by means of a colorimetric technique developed by Dietrich et al. (2013) [2]. This technique is based on the use of Resazurin as an oxygen sensitive dye which when subjected to an oxidation/reduction reaction, presents the property to achieve an intense color (pink and fluorescent) in the oxidized or reduced state, and colorless (not fluorescent) in the conjugate (opposite) state. That fact allows link the color of the acquired images with the presence of oxygen. The innovation introduced is the image acquisition in different points with the aims at studying the change of mass transfer along the length of the channel and also the effect of channel bends in mass transfer. An image acquisition in the vertical plane (Oxz) has been carried out to appreciate the effect of the gravity in the bubbles and find new perspectives for visualizing gas-liquid transfer along the channel depth.

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