Taylor flow CO2 chemical absorption in a minichannel: Characterization of transport behaviors in the liquid slug and mass transfer modeling

Abstract

This paper presents the mass transfer behaviors accompanied by chemical reaction under Taylor flow pattern. Experiments were conducted to study the absorption of CO₂ into MEA aqueous solution in a vertical straight minichannel with square cross-section of 1.5 mm in width. The velocity field in the liquid slug was characterized using particle tracking velocimetry (PTV), revealing a liquid internal recirculation pattern featuring dual vortex symmetry structure. The recirculation intensity increased with higher two-phase velocities and MEA concentration, and was accurately predicted using a proposed empirical correlation. A pH-sensitive colorimetric method was employed to measure the spatial and temporal distribution of CO₂ concentration within the liquid slug. High CO₂ concentration zones were observed near bubble caps and channel walls, while low concentration zones were identified in the liquid bulk. Although liquid recirculation motion significantly enhanced axial convection-driven mass transfer, radial mass transfer remained diffusion-dominated. To better account for these phenomena, a modified unit-cell flow and mass transfer model was developed, incorporating the enhancing effects of liquid flow recirculation and chemical reaction. This model enables the determination of local mass transfer coefficients within the liquid slug, offering new insights into the transport mechanisms at the local level.