Volume-of-fluid simulations of gas-liquid-liquid flows in minichannels

Three-phase segmented gas-liquid-liquid (G/L/L) flows in minichannels are important to several chemical process applications involving gas-liquid-liquid reactions. In the present work, we have investigated segmented G/L/L flows in a double T-junction minichannel, with cross-section of 0.95 mm x 1 mm, through high-speed imaging experiments and Volume-of-Fluid (VOF) simulations. The dynamics of bubble/slug formation at the 1st T-junction and importantly that of water drop/slug formation at the 2nd T-junction was simulated under different flow conditions (Ca-oil = 2.63 x 10(-3)-1.101; We(air) = 4.24 x 10(-4)-2.62 x 10(-3); We(water) = 0.0431-7.14) and different surfactant concentrations (0.3 and 2 wt/wt.%) in aqueous phase. The predicted formation mechanisms, three-phase flow regimes, and drop/bubble/slug lengths were compared quantitatively with the measurements. Different mechanisms of bubble/slug formation observed for the aforementioned range of the Caoil and Weair, and bubble/slug lengths were predicted in a satisfactory agreement with the measurements. The complex formation mechanism of water drops/slugs that was governed by viscous force exerted by continuous oil phase, inertial force exerted by water phase, interfacial tension force acting on the oil-water interface and also by incoming air bubbles/slugs; could be predicted in a satisfactory agreement with those observed in the experiments. Different three-phase flow regimes, e.g., drop-bubble, drop-slug and slug-slug, observed for different oil, air and water flow rates; and for different values of oil-water interfacial tensions are also predicted in satisfactory agreement with the measurements. The results reported in the present work help to understand the hydrodynamics of complex three-phase gas-liquid-liquid flows in minichannels, which in turn is crucial to device microreactor systems for process applications involving G/L/L flows.