Visual Study of Droplet Bouncing Phenomena upon Impact on Hot Horizontal Surface

When a droplet hits a hot surface beyond the Leidenfrost temperature, the droplet will bounce on the hot surface. This unique bouncing phenomenon only occurs in the film boiling region. This paper discusses the relationship between the residence time of droplet and droplet bouncing phenomena during droplet impact on hot horizontal surfaces. In this experiment, aluminum (mirror polished) was selected as a test surface. Degassed and distilled water were used in the experiment. The droplet diameter was fixed at 4.0 mm and the droplet temperature was kept at 16.0 °C. The droplet falling height was fixed at 65.0 mm corresponding to the impact velocity of 1.129 m/s. This unique droplet bouncing phenomenon was recorded at 10,000 fps (frames per second) by using a high speed video camera. From the theoretical calculation, the residence time or liquid-solid contact time of droplet during impact on hot surface was approximately 23.0 ms. Therefore, it is found that the measured residence time from the experimental data agrees closely with the theoretical calculation.