Gas Flow Dynamics between a Leidenfrost Water Droplet and Micro-sized Asymmetric Heated Surface

摘要

A water droplet placed on an asymmetric surface, superheated above the Leidenfrost temperature, not only levitates, but also self-propels in a well-defined direction and speed. Some researchers have pointed out that this self-propulsion is caused by the vapor flow due to evaporation, that is rectified by the asymmetric shape of the surface. However, a totally different mechanism was also proposed, where the large non-uniform temperature gradient across the asymmetric surface creates a strong thermal creep flow that drags the droplet in a unidirectional motion, which becomes more significant as the length scale approaches micro level. In this research, the gas dynamics behind this phenomenon is studied by considering the contributions of the vapor flow and thermal creep flow by numerical analysis using the DSMC method for ratchet shaped and tilted pillar shaped surfaces.