Plasma irradiation is one of the techniques to improve surface wettability. This technique can be used to enhance heat transfer of liquid-vapor phase change. For instance, evaporation of a water droplet can be enhanced by plasma irradiation. The relation between plasma irradiation time and contact angle was examined first for three metals and then the lifetime of a water drop on a hot surface was measured changing the surface wettability by plasma irradiation. The lifetime of the water drop decreased and the wetting limit temperature increased with the increasing irradiation time of plasma. Hydrophilicity by plasma irradiation is not a permanent effect but it will be useful for enhancement of cooling of hot metal.
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