Experimental and numerical investigation of gas-side mass transfer in Taylor flow

Abstract

Taylor flows are of great interest for industrial application where efficient gas absorption is needed. Literature however scarcely relates to the gas-side mass transfer coefficient kG in Taylor flows. In this work, the authors selected and developed an experimental method, based on bubble expansion record, to estimate kG value in a millimetric channel of circular section, fed with nitrogen gas and pure ethyl acetate (EA). The experiments provided an order of magnitude of a few mm.s−1 at least for kG, for a two-phase velocity UTP ∼ 0.1 m.s−1.CFD simulations completed the experimental investigation and further estimated the order of magnitude, with kG∼10-2 m.s−1 when 0.09<UTP<0.18 m.s−1. The transport of EA inside the bubble suggests a significant contribution of diffusion in regard with the convective effects. kG is found to be sensitive to UTP, and to the temperature via the gas diffusivity and also via the bubble expansion leading to an increase in bubble velocity. The dependence of the gas-side Sherwood number to the Péclet number is similar to previously reported observations concerning a spherical bubble freely rising in quiescent liquid.This study thus provides the means to evaluate the gas-side resistance for any gas–liquid system in Taylor flows, a resistance that was usually simply dismissed in previous works. As an example, the authors demonstrated that, in Taylor flows, for a gas–liquid system of industrial interest (diluted CO2 in 30 wt.% N-methyldiethanolamine aqueous solution), gas-side mass transfer resistance is lower than the liquid-side one by at least one order of magnitude.