78th Annual Meeting of the APS Division of Fluid Dynamics (Nov 23 — 25, 2025)

V058: Air Entrainment Process From Elongated Bubbles

This work explores the behavior of elongated bubbles in slug flow inside pipes, focusing on air entrainment at the bubble rear. In experiments, we observed how bubbles deform over time, how the thin liquid film drains along the wall, and how small gas filaments form behind the bubble depending on the flow regime. Using high-speed imaging and image processing, we tracked the degradation of the quase static elongated bubble. The liquid film can pull air into the recirculation wake, where the vortex flow stretches and twists the filaments, eventually causing stochastic breakup. This process, governed by the balance between surface tension, inertia, viscosity, and gravity, makes the exact timing and location of filament breakup unpredictable. Observing transient bursting bubbles provides a practical way to estimate local air release rates (future work). These experiments show that air entrainment strongly depends on the rear liquid film and wake structure, confirming that filament breakup is largely stochastic. Our findings enhance understanding of entrainment mechanisms in slug flows and can support both statistical and computational models, with applications for controlling multiphase flow in industrial pipelines.