The effects of the surface roughness on the dynamic behavior of the successive micrometric droplets impacting onto inclined hot surfaces

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 degrees, 30 degrees, and 45 degrees from horizontal. The droplet diameters were 500 mu m and 700 mu m. The solid surface temperatures were decreased from 500 degrees C to 100 degrees 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. (C) 2016 Elsevier Ltd. All rights reserved.