A visualization study on the dynamic characteristics of two droplets impinging onto a hot plate was carried out. The sapphire plate was heated up to 300ºC by a brass casting heater. Two high speed cameras were used for side and bottom view visualization, and the frame rate was 20000 fps. De-ionized water droplet was made through a 31G injection needle and the droplet diameter (D) was 2.4 mm. The distances between two droplets were 1D and 2D. Weber number was fixed to 25. In case of 200ºC condition (CHF condition), the droplets were attached to the surface and showed vibrations with boiling. In case of 300 ºC surface (Leidenfrost condition), the droplets spread then bounced back like a single droplet impinged onto a super hydrophobic surface. 2D separation distance of droplets rebounded 2 times higher then that of 1D separation distance. As increasing the time difference of impingement between two droplets, the rebound height of droplets were increased due to lower energy losses between two droplets.
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