CFD simulation of liquid-liquid extraction mechanism and enhancement schemes in microchannels based on three mass transfer models

Microreactors are highly efficient devices with a large specific surface area to improve the mass transfer efficiency. In this paper, a comprehensive three-dimensional CFD model was constructed based on three mass transfer theories to simulate the liquid-liquid two-phase flow and mass transfer process in a microchannel reactor, and two enhancement schemes were proposed. The multiphase flow and mass transfer characteristics were investigated by visualization and extraction experiments. The results indicated that the extraction efficiencies (E) and overall mass transfer coefficients ($K_{L}a$) calculated by the penetration model and surface renewal model were within $\pm$15 % errors compared to the experimental values. Moreover, E primarily increases with the increase of fluid residence time, while $K_{L}a$ increases with increasing flow rate. As the flow rate increases from 0.3 ml/min to 1.5 ml/min, E decreases by 15 %, and $K_{L}a$ rises from 0.78 s⁻¹ to 2.65 s⁻¹. Whereas the channel width decreases from 0.8 mm to 0.3 mm, E decreases by 3 %, and $K_{L}a$ rises from 0.44 s⁻¹ to 2.77 s⁻¹. Finally, microchannel with necked structure and baffles in mixing zone both improve the mass transfer efficient to some extent.