Experimental Study on Oblique Collisions of Water Droplets With Hot Solid

The oblique collision of single water droplets with a hot Inconel 625 alloy surface has been investigated by means of a two-directional flash photography technique that uses two digital still cameras and three flash units. The experiments were conducted under the following conditions. The pre-impact diameter of the droplets was approximately 0.6 mm, the impact velocity was 1.9–3.0 m/s, and the temperature of the Inconel 625 alloy surface ranged from 170 °C to 500 °C. The impact angle of the horizontal line to the tilted solid surface was 30°. When a droplet impacts a solid at a temperature of 200 °C with an impact velocity of approximately 2.0 m/s, many boiling vapor bubbles are formed at the liquid/solid interface. The droplet deforms into an asymmetric disk and moves downward along the tilted surface. Numerous secondary droplets jet upward from the deforming droplet due to the blowout of the vapor bubbles into the atmosphere. At a surface temperature of 500 °C, no secondary droplets are observed. The droplet rebounds off the solid without disintegration. The shape of the droplet is almost axisymmetric during the collision. Experiments using 2.5-mm-diameter droplets at an impact velocity of approximately 1.0 m/s were also conducted. The dimensionless collision behaviors of large and small droplets were compared under the same Weber number conditions. At a surface temperature of 500 °C, the two dimensionless deformation behaviors of the droplets are similar to each other. The hydrodynamics and boiling phenomena of the droplets were investigated in detail.