Hydrodynamic and mass transfer in inertial gas–liquid flow regimes through straight and meandering millimetric square channels

Heat-exchanger reactors are an important part of process intensification technology. For plate geometries, one solution for intensifying transfer and increasing residence times is to construct two-dimensional meandering channels. Supported by this scientific context, the present work aims at characterising gas–liquid mass transfer in the same square millimetric meandering channel, as in Anxionnaz (2009), this constituted the preliminary step required for performing exothermic gas–liquid reactions. Firstly, the gas–liquid hydrodynamics were characterised for a water/air system. When compared to a straight channel of identical compactness and sectional-area (2×2 mm²), the meandering channel induced (i) a delay in the transition from Taylor to annular-slug regimes, (ii) a rise of 10–20% in bubble lengths while conserving almost identical slug lengths, (iii) higher deformations of bubble nose and rear due to centrifugal forces (bends). Secondly, an original method for verifying the relevancy of the plug flow model and accurately determining k_la was used (measurements of concentrations in dissolved oxygen along the channel length). For the Taylor flow regime, k_la increased coherently when increasing j_g, and the meandering geometry had a small influence. On the contrary, this effect was found no more negligible for the slug-annular flow regime. Whatever the channels, the NTU_l remained low, thus showing that, even if millimetric channels allowed to intensify k_la, a special attention should be paid for generating sufficient residence times. At identical compactness, the meandering channel was found to be the most competitive. Finally, results on gas–liquid interfacial areas and mass transfer coefficients were confronted and discussed with respect to the predictions issued from the model developed by Van Baten and Krishna (2004).