Behavior of Small Droplet Impinging on a Hot Surface

The effects of droplet diameter, surface roughness, and impinging velocity on the behavior of a droplet impinging on a hot surface were studied. The surface samples used in the experiment were cylinder blocks of stainless steel having four different degrees of roughness: Ra 0.04, Ra 0.2, Ra 3, and Ra 10. The diameter and impinging velocity were controlled independently using a microjet dispenser, and their values were in the ranges of 300-700m and 1.0-4.0m/s, respectively. The contact time was found to increase with an increase in the surface roughness and was of the order of the self-oscillation of the water droplet. The maximum spread of the droplet decreased with increasing impinging velocity. A cooling curve was obtained for surface temperatures ranging from 500 degrees C to 100 degrees C, and the cooling time was found to decrease with an increase in the surface roughness of stainless steel. Moreover, the cooling effectiveness of each droplet increased with an increase in the surface roughness, a decrease in the droplet diameter, and an increase in the impinging velocity.