Development of Rapid Cooling Method Using Wetting Improvement by Plasma Irradiation

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The purpose of this research project is to develop an enhanced cooling method making use of plasma irradiation which enhances surface wattability of various solid surfaces.Three metals, aluminum, copper and stainless steel were selected as the test materials. First, the following were investigated experimentally to understand the fundamental characteristics and relationship between plasma irradiation and surface wettablity ;(1)change in contact angle with irradiation time of plasma.(2)Recovery process of surfaces from hydrophilic state to hydrophobic state, namely, relationship between contact angle and elapsed time after termination of irradiation.As a result, it was turned out that aluminum was the best among three metals. The contact angle of aluminum decreased to nearly zero, while the terminal contact angles of copper and stainless steel during irradiation were nearly 10 degree. In case of aluminum, special treatment has also been done on its surface to have a fractal surface structure. This surface initially had a superhydrophilic nature, but it gradually changed and finally became super-water-repellent.In order to know the cooling ability, experiments of water drop evaporation using above surfaces have conducted and the following results were obtained ;(1)When the surface temperature was 50 degree C, evaporation time of water drop depended on contact angle. By the decrease in contact angle, evaporation time was drastically decreased and the evaporation was enhanced by the improvement of surface wettablity.(2)The wetting limit temperature increased with the decrease in contact angle. In case of aluminum and copper, the wetting limit temperature increased by 45K by the plasma irradiation.It was found that the wetting improvement by plasma irradiation was one of the promising methods of rapid cooling technique.