Experimental Mapping of Air–Water Two-Phase Flows: Configuration and Injection Effects in T-Junction Minichannels

This paper investigates air–water two-phase flow regimes in a horizontal T-junction mini-channel with a 1 × 1 mm2 main mini-channel and a 0.3 × 0.3 mm2 side channel. The resulting cross-sectional area ratio of about 11:1 lies outside the range covered by most previous studies. Two injection configurations were compared systematically: in the first, air flows through the main channel and water enters through the side branch; in the second, the two ports are swapped. In the first configuration, the gas superficial velocity ranged from Jg = 1.7 × 10−3 to 1.5 m/s and the liquid superficial velocity from Jℓ = 2.7 × 10−3 to 0.1 m/s. In the second, Jg ranged from 1.5 × 10−2 to 12.5 m/s and Jℓ from 1.7 × 10−3 to 0.28 m/s. Six flow regimes were identified: monodispersed bubbles, slug–bubbles, slug–bubble–-slug, slug, wavy annular and annular flow. From these observations, flow maps were built for each configuration: one in terms of the superficial velocities Jg and Jℓ and one in terms of the momentum flux ratio XM and the gas Weber number Weg. The maps show that the flow pattern is strongly sensitive to the injection mode, and that the transition boundaries deviate substantially from those of maps in literature. The set of regimes itself also depends on the configuration. Slug–bubble–slug and annular flows occur only in the first configuration, whereas monodispersed bubbles, slug–bubbles and wavy annular flow occur only in the second. Slug flow is the only regime common to both. For instance, direct visual observation at identical flow rates confirms that the injection configuration alone determines the resulting flow pattern. To the best of our knowledge, such a configuration-dependent set of regimes has not been reported before for this geometry.