An Experimental Study on the Oblique Collisions of Water Droplets With a Smooth Hot Solid

摘要

The motions of liquid droplets impinging on a solid substrate have been studied experimentally in fundamental research on various types of industrial applications, including spray cooling. The oblique collision of a single water droplet 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 preimpact diameter of the droplets was approximately 0.6 mm, the impact velocity was 1.9-3.1 m/s, and the temperature of the Inconel 625 alloy surface ranged from 170 deg C to 500 deg C. The impact angle of droplets on the solid surface was in the range 45 deg-90 deg. Experiments using 2.5 mm diameter droplets at an impact velocity of 0.84-1.4 m/s were also conducted at the surface temperature of 500 deg C. At surface temperatures of 200 deg C, 300 deg C, and 400 deg C, the droplet deforms into an asymmetric shape and moves downward along the tilted surface. Numerous secondary droplets jet upward from the deforming droplet as a result of the blowout of vapor bubbles into the atmosphere. At a surface temperature of 500 deg C and a low Weber number We_(n) based on the normal velocity component to the solid surface, no secondary droplets are observed. The droplet rebounds off the solid without disintegrating. The droplet becomes almost axisymmetric in shape during the collision regardless of the impact angle. The dimensionless collision behaviors of large and small droplets were similar for the same We_(n) when the temperature was 500 deg C. Using We_(n), we investigated the deformation characteristics of droplets in oblique collisions.