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Abstract: The effect of surface wettability on the collision dynamics and heat transfer phenomena of a single water droplet impacting upon a heated solid surface has been studied experimentally. To modify the surface wettability, two modules of stainless steel coated by TiO2 were employed. The first module was induced by ultraviolet irradiation to produce the hydrophilic surface, while the second one was not. The diameter and the depth of coating surface were 30mm and 200nm, respectively. The droplet size was varied from 1.90 to 2.90mm and substrate temperature raised up to 340°C. The interaction of an impact water droplet with a heated solid surface was investigated using a high-speed video camera. As a result, it was found that; (1) in the lower surface temperature region the evaporation time decreases as the static contact angle decreases, (2) the wetting limit temperature decreases with the increase of static contact angle, (3) the ultraviolet irradiation on the TiO2 surface does not change the qualitative behavior of the evolution of wetting diameters, and (4) the maximum wetting diameter increases with the decrease of static contact angle below the wetting limit temperatures. [Copyright &y& Elsevier]

The effect of surface roughness on the dynamic behavior and the heat transfer phenomena of multiple successive micrometric water droplets impacting onto inclined heated solid surfaces has been studied experimentally. The inclination angles were 15°, 30°, and 45° from horizontal. The droplet diameters were 500 μm and 700 μm. The solid surface temperatures were decreased from 500 °C to 100 °C. The test material was stainless steel-grade 304 (SUS 304) with different surface roughness ranged from Ra 0.04 up to Ra 10. The droplet dynamics during the impacting onto inclined hot surfaces were investigated by using high-speed video camera. It was found that the surface roughness significantly affects quenching behavior. The higher the surface roughness, the lower the quenching time during the spray cooling. The solid-droplet contact time and the droplet spread diameter increase with the increase of surface roughness. Thus causing the decrease of the quenching time of inclined hot walls. Meanwhile, the critical heat flux and Leidenfrost temperatures are shown to be insensitive to the surface roughness. [ABSTRACT FROM AUTHOR]