Development of Rapid Cooling Method Using Wetting Improvement by Plasma Irradiation

本研究的目的是开发一种利用等离子体辐照的强化冷却方法，以提高各种固体表面的表面瓦特率，选择三种金属，铝，铜和不锈钢作为试验材料。首先，通过实验研究了等离子体辐照与表面润湿性之间的基本特性和关系：（1）接触角随等离子体辐照时间的变化。（2）表面从亲水状态到疏水状态的恢复过程，即照射结束后接触角与经过时间的关系，结果表明，铝是三种金属中最好的。铝的接触角在辐照过程中下降至接近零，而铜和不锈钢的末端接触角在辐照过程中接近10度。在铝的情况下，在其表面上也进行了特殊处理以具有分形表面结构。为了了解这种表面的冷却能力，进行了水滴蒸发实验，得到以下结果：（1）当表面温度为50 ℃时，水滴蒸发时间与接触角有关;通过减小接触角，蒸发时间大大缩短，并且通过改善表面润湿性来增强蒸发。（2）润湿极限温度随接触角的减小而升高。对于铝和铜，等离子体辐照使润湿极限温度提高了45 K，发现等离子体辐照改善润湿是一种很有前途的快速冷却技术。

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.