Bubble formation and local mass transfer attenuation in a serpentine microchannel

This study experimentally investigates two key fluid mechanical behaviors in gas–liquid two-phase flow within a square-section serpentine microchannel: the curvature-induced satellite bubble formation mechanism and the axial decay of local mass transfer. Experiments were conducted using carbon dioxide (CO₂) and an aqueous solution containing 0.4 wt. % sodium dodecyl sulfate. Various flow patterns were observed, including long slug–long slug flow (LS–LS), long slug–slug flow (LS–S), slug–slug flow (S–S), slug–droplet flow (S–D), droplet–droplet flow (D–D) and slug–satellite flow (S–SL). Notably, when the gas–iquid total volumetric flow rate exceeded 500 ml/h, a distinctive satellite bubble generation phenomenon was observed at the channel bend. High-speed imaging revealed the underlying mechanism: centrifugal force causes the bubble tail to detach from the inner wall, followed by neck thinning and rupture under the combined action of liquid-phase inertial stretching and capillary pinch-off. Analysis of flow parameters indicates that bubble volume and generation frequency are governed by gas–liquid shear competition, while the pressure drop is primarily controlled by the gas phase velocity. The liquid-side mass transfer coefficient is dominated by the liquid-phase velocity, reflecting the crucial role of liquid-phase internal circulation in interface renewal. To quantify the spatial evolution of mass transfer, the channel was divided into ten consecutive segments. The results show that the liquid-side local mass transfer coefficient first decays rapidly along the flow direction and then levels off, indicating that the effective mass transfer process is highly concentrated in the front section of the channel. These findings provide a physical basis for understanding interfacial instability and mass transfer localization in curved microchannels.