Development of Rapid Cooling Method Using Wetting Improvement by Plasma Irradiation

本研究项目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可瓦性。试验材料选用铝、铜、不锈钢三种金属。首先，通过实验研究了解等离子体辐照与表面润湿性的基本特性和关系；(1)等离子体接触角随辐照时间的变化。(2)表面从亲疏水状态恢复到疏水状态的过程，即辐照终止后接触角与时间的关系。结果表明，铝是三种金属中最好的。在辐照过程中，铝的接触角减小到接近零，而铜和不锈钢的接触角接近10度。就铝而言，其表面也进行了特殊处理，使其具有分形表面结构。这种表面最初具有超亲水性，但它逐渐改变，最终成为超拒水性。为了了解其冷却能力，在上述表面进行了水滴蒸发实验，得到了以下结果：(1)当表面温度为50℃时，水滴的蒸发时间与接触角有关。随着接触角的减小，蒸发时间大大缩短，表面润湿性的提高促进了蒸发。(2)润湿极限温度随接触角的减小而增大。等离子体辐照使铝和铜的润湿极限温度提高了45K。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.