The effect of coalescence angle on bubble departure: Insights from dynamic observations and simulations

This study uses a self-developed 3D coalescence-induced bubble departure visualization system and numerical simulations to explore the regulatory mechanism of coalescence angle (ω) on bubble detachment. Results show that as ω decreases (90°→20°), the three-phase contact line transitions from “bidirectional synchronous contraction − asynchronous contraction − unilateral diffusion”, enhancing contact angle hysteresis and shifting bubble motion from vertical detachment to horizontal sliding. When the surface contact angle exceeds 60°, bubble detachment is fully suppressed, and ω loses its effect. Phase diagram analysis reveals that surface hydrophobicity and coalescence angle control detachment through competing adhesion forces and flow field momentum. Large ω (≥70°) generates vertical momentum (Re = 120, We = 0.27) to drive detachment, while small ω (≤45°) causes horizontal oscillations (Re = 70, We = 0.11) and energy dissipation. A critical criterion based on the balance model of surface energy and viscous resistance work quantifies the energy thresholds for bubble detachment under different operating conditions, offering insights for optimizing industrial bubble dynamics.