Experimental Investigation of Droplets Impacting on Inclined Heated Surfaces with Varying Wettability*

Droplets impacting on heated surfaces is a common phenomenon in spray cooling, which can remove very high heat flux. Since the surface wettability has a significant effect on the heat transfer performance by directly changing the droplet spreading, rebounding and boiling behaviors, it has drawn much attention. However, the surface roughness changes simultaneously when changing the surface wettability in most researches. Thus, the influence factors of wettability and roughness are coupled. In this work, the test surfaces were fabricated by spray-coating a thin film on the aluminum substrates and the roughness of each surface is small enough. Therefore, the influence of wettability on droplets impacting on inclined heated surfaces have been experimentally studied. The experiments were carried out with different inclination of 0^o, 30^o and 60^o, with different surface temperature from 100^oC to 400^oC and with different surface contact angle of 10^o, 78^o, 95^o and 122^o. The droplet spreading, rebounding and boiling behaviors have been observed by a high speed camera. The droplet spreading factors, advancing and receding contact angles have been measured and the droplet boiling regimes have been identified.