Study of explosive lift-off phenomenon in water drop impingement on the heated surfaces with micro-pillars

Abstract

Although it is a common phenomenon, a general understanding of drop impact remains elusive because its dynamics are extremely fast and influenced by numerous parameters. The outcomes of drop impact are affected by the surface geometry and wall temperature. With the development of surface modification, faster and more complex drop impact dynamics are observed on superheated and modified surfaces. In this study, drop impingement and pool boiling experiments were conducted to reveal the physical mechanisms governing the drop impact dynamics on a superheated surface with micro-pillars. The surface was characterized by micro-pillars fabricated with microelectromechanical systems to conduct a quantitative experiment. Drop impingement was conducted to identify the drop impact dynamics on a superheated surface with micro-pillars. Pool boiling experiments were conducted to evaluate the pool boiling characteristics on a surface with micro-pillars and verify the hypothesis suggested by previous researchers. Additionally, a hypothesis of the triggering mechanism of an explosive lift-off is presented based on the relation between the change in critical heat flux and the occurrence of explosive lift-off. A theoretical model is developed based on the force balance and liquid–vapor interface behavior during drop impact. The theoretical model of the explosive lift-off triggering mechanism is verified by visualizing the liquid–vapor interface behavior during drop impact using ultra-fast synchrotron X-ray imaging with high spatial (1 μm/pixel) and time (~271,552 Hz) resolutions. It was shown that, in drop impact phenomena, the microscopic liquid–vapor interface motion determines the macroscopic motion of the impinging drop.