Characteristics map of dynamic behavior of a droplet impinging onto an inclined hot surface

Abstract

The dynamic behavior of a droplet impinging on a hot surface was examined experimentally using high-speed cameras. De-ionized water droplets with a diameter of 2.25 mm were generated through a 31G injection needle. A sapphire plate with inclination angles ranging from 0° to 60° was heated to 300 °C on a hotplate. Two high-speed cameras with frame rates of 20,000 frames per second were used to visualize the dynamic behavior of water droplets. The Weber number was varied from 5 to 123 by changing the initial height of the droplet from 40 to 210 mm. This corresponds to a normal Weber number range of 6–34 for an inclination angle of 60°. The dynamic behavior of the droplet after impingement was strongly dependent on the surface temperature, inclination angle and Weber number. At lower inclination angles, micro-explosions were observed when the surface temperature was at the Leidenfrost condition. At higher inclination angles, the impinging droplet tended to recover its original spherical shape due to the vapor cushion at the Leidenfrost condition. With increasing Weber number, both maximum spreading diameter and sliding length were increased.