Investigation on Dynamic Properties and Heat Transfer Mechanism of Droplet Impact on the Heated Wall Under a Leidenfrost State

In order to explore the dynamic properties and heat transfer mechanism of droplet impact on the heated wall, this study employs numerical simulation to analyze the Leidenfrost phenomenon caused by droplet impact. The occurrence mechanism of Leidenfrost phenomenon is analyzed from various perspectives, including droplet morphology, gas film formation, and interaction with the heated wall. The study reveals that the droplet, gas film, and heated surface mutually influence each other. As the droplet evaporates, water vapor is produced, and the gas film prevents direct contact between the droplet and the heated wall, resulting in the Leidenfrost phenomenon. The effects of droplet impact velocity, droplet size, and wall temperature on the Leidenfrost phenomenon were further investigated. The results indicate that a higher droplet impact velocity results in increased kinetic energy and a higher spreading coefficient, leading to enhanced heat exchange ability. However, the time taken to reach the maximum spreading coefficient differs from that of non-phase-change droplets. Additionally, smaller droplet sizes exhibit a more significant effect of surface tension on maintaining droplet shape. This results in a shorter spreading time for the droplet, but also higher kinetic energy consumption and a relatively smaller spreading coefficient. For the heat flow density, the larger impact velocity and size of droplet can increase the heat flow density and improve heat transfer. An increase in wall temperature significantly increases the heat flow density and is a crucial factor in sustaining the droplet Leidenfrost phenomenon.