Study on the behavior of small droplet impinging onto a hot surface

Abstract

The effects of droplet diameter, surface roughness, and impinging velocity on the behavior of droplet impinging onto a hot surface have been studied. The surface samples used in the experiment were cylinder blocks of stainless steel having four different degrees of roughness, i.e., Ra 0.04, 0.2, 3, and 10. The diameter and impinging velocity were controlled independently by using a micro-jet dispenser. Their values were in the ranges of 300–700 μm and 1.0–4.0 m/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 droplet decreased with increasing impinging velocity. The cooling curve was obtained for the range of surface temperatures from 500 oC to 100 oC, and it was found that the cooling time decreased 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.