Explosive lift-off triggering mechanism on a surface with micropillar arrays: Liquid-vapor interface behavior between micropillars during drop impingement

Generally, three classified hydrodynamic behaviors of impinging water drops involving corresponding boiling heat transfer regimes have been reported under low Weber number conditions (We < 20): contact boiling (nucleate boiling), transition rebound (transition boiling), and Leidenfrost rebound (film boiling). In previous studies of drop impingement on a structured surface, an explosive lift-off regime, which is characterized by lift-off from the surface within 1 ms without any disturbance at the top side of the drop, was reported, and the triggering hypothesis of explosive lift-off suggested had no quantitative evidence. In this study, the outcomes of water drop impingement onto a heated surface with micropillar arrays were investigated using a high-speed imaging system, for wall temperatures between 150 and 380 degrees C and a Weber number of approximately 4. Pool boiling experiments were conducted to validate the triggering hypothesis of explosive lift-off, as suggested by previous researchers. Based on the experimental results, the triggering mechanism of the explosive lift-off is discussed.