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Journal of Enhanced Heat Transfer

Impact factor: 0.400

ISSN Print: 1065-5131
ISSN Online: 1563-5074

Journal of Enhanced Heat Transfer


pages 73-81

Enhancement of Evaporation of a Liquid Droplet using EHD Effect: Criteria for Instability of Gas-Liquid Interface Under Electric Field

Kiyoshi Takano
Institute of Industrial Science, University of Tokyo 7-22-1, Roppongi, Minato-ku, Tokyo, 106, JAPAN
Ichiro Tanasawa
Department of Mechanical Engineering, Nihon University, 1 Tokusada, Tamura-cho, Kooriyama-shi, Fukushima 963-8642, Japan
Shigefumi Nishio
Key Laboratory of Enhanced Heat Transfe and Energy Conservation, Ministry of Education, School of Chemical and Energy Engineering, South China University of Technology, China; and Institute of Industrial Science and Technology, University of Tokyo, Japan

ABSTRACT

It was confirmed, in the preceding study, that an evaporation of a liquid droplet on a heated surface was enhanced to a great extent by applying an electric field. Visual observation of the evaporation process indicated that small columns of the liquid were formed underneath the bottom of the droplet, causing direct contact between the liquid and the solid surface. The direct contact underneath the bottom of the droplet was considered to be induced by the interfacial instability due to the electric field. In the present study, an experiment was carried out to clarify the mechanism that an electric field induced the instability of a liquid surface. The static electric voltage was applied between the liquid surface and a horizontal planer electrode placed over the surface. The applied voltage was raised gradually until the liquid surface became unstable. The threshold voltages were measured for different distances between the electrode and the liquid surface and for different liquids. The test liquids used in the experiment were water, ethanol, refrigerant Rl 13, carbon tetrachloride and cyclohexane. The visual observation of the process leading to destabilization of the liquid surfaces was performed using a high-speed video facility. Criteria for the onset of instability were derived analytically using a modified Rayleigh-Taylor instability equation, finding that the theoretical results agreed very well with the experimental data. In addition, the temperature of the heat transfer surface above which the drop evaporation was enhanced was predicted using the result of the instability analysis.