Investigation of mass transfer in valve-controlled gas-liquid segmented flow

Segment flow is widely employed in gas-liquid microreactor systems owing to its enhanced mass transfer through the biphasic interface. Previous studies evaluating an increased fluid flow rate (F) have reported an increased volumetric mass transfer coefficient (kLa) and reduced segment length (L). In a conventional microsystem, manipulating L without varying the residence time of the fluids is challenging. Hence, the relationship between kLa and L has not been systemically investigated under the same F. In this study, L control without changing F is implemented by introducing a high-speed valve into a gas-liquid microchannel system, and the influence of L on kLa is investigated by altering the valve frequency (f). The results indicate that kLa in the segmented flow is negatively correlated with L at constant F and reaches 0.149 s-1 (332.6 times larger than that in the bubble), whereas the specific area (a) of the segmented flow increases with increasing f before the liquid phase is saturated. Moreover, a and instinct kLa can be predicted using f, F, and the microchannel diameter. The outcomes of this research will improve the understanding of the mass transfer phenomenon in gas-liquid segmented flows and provide support for the design of microreactor systems.