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First Thermal and Fluids Engineering Summer Conference

ISSN: 2379-1748
ISBN: 978-1-56700-430-4

SEMI-EMPIRICAL MOEL OF MICRO WATER DROPLET ON LOW SURFACE ENERGY SOLID UNDER THE NATURAL EVAPORATION

DOI: 10.1615/TFESC1.mph.012691
pages 1997-2003

Yukihiro Yonemoto
Priority Organization for Innovation and Excellence, Kumamoto University, 2-39-1 Kurokami, Chuo, Kumamoto 860-8555, Japan

Tomoaki Kunugi
Department of Nuclear Engineering, Kyoto University, C3-d2S06, Kyoto Daigaku-Katsura, Nishikyo-ku, Kyoto 615-8540, Japan


KEY WORDS: Wettability, microdroplet, natural evaporation

Abstract

Wetting phenomenon is related to improvement of energy efficiency of many industrial devices such as heat exchanger and nuclear power plant. However, in spite of the fact that the application of wetting phenomenon is beneficial for many industrial devices, theoretical discussion is insufficient with respect to the wetting phenomenon. Wettability is mainly related to an interaction between liquid and solid and is characterized by a contact angle. When the volume of a droplet on a solid surface decreases due to phase change such as evaporation, there are two stages for the droplet behaviors. At first, the contact angle decreases with the constant contact area. Then, after reaching a certain value of the contact angle, the contact line starts to recede. Former stage is called a contact angle hysteresis. Latter stage is called a size dependence of the contact angle. Especially, the latter stage is usually explained by using the modified Young equation where the line tension is explicitly added. The line tension was firstly introduced by Gibbs and is assumed as a negative and constant value. However, it is observed that the line tension is not constant and depends on the droplet size. In the present study, the droplet behaviors under the natural evaporation are considered experimentally. The semi-empirical models are proposed and compared with the experimental data.

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