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International Heat Transfer Conference 15

ISSN: 2377-424X (online)
ISSN: 2377-4371 (flashdrive)

Wettability-Driven Water Condensation at the Micron and Submicron Scale

Yutaka Yamada
Graduate School of Natural Science and Technology, Okayama University, 3-1-1, Tsushimanaka, Kita-ku, Okayama 700-8530, Japan

Akira Kusaba
Department of Aeronautics and Astronautics, Kyusyu University

Tatsuya Ikuta
Department of Aeronautics and Astronautics, Kyusyu University

Takashi Nishiyama
Department of Aeronautics and Astronautics, Kyusyu University

Koji Takahashi
Department of Aeronautics and Astronautics, Kyushu University, Motooka 744, Nishi-Ku, Fukuoka 819-0395, Japan; International Institute for Carbon-Neutral Energy Research (WPI-I2CNER), Kyushu University, Motooka 744, Nishi-Ku, Fukuoka 819-0395, Japan

Yasuyuki Takata
Department of Mechanical Engineering, Thermofluid Physics Laboratory, Kyushu University, 744 Motooka, Nishi-ku, Fukuoka, 819-0395, Japan; International Institute for Carbon-Neutral Energy Research (WPI-I2CNER), 744 Motooka, Nishi-ku, Fukuoka 819-0395, Japan

DOI: 10.1615/IHTC15.cds.009177
pages 827-834


KEY WORDS: Condensation, Heat exchanger, ESEM, Wettability

Abstract

Water condensation on a graphite surface was investigated at the micron and submicron scale by environmental scanning electron microscopy. The graphite comprised a hydrophobic terrace and hydrophilic step edges, of which the nanoscale structure was precisely measured by atomic force microscopy prior to the condensation experiments. The condensed droplets were preferentially aligned parallel to the step edges with a step height of 1 nm. The droplets featured a diameter of 150–300 nm at intervals greater than 150 nm. Shorter droplet intervals were realized by narrower terraces and higher steps. The current findings extend beyond the nucleation theory, whereby the effect of adsorbed water molecules on hydrophilic step edges was considered. The contact angle (i.e., 10°) of the nucleated droplet at its initial stage (with diameter in the nanoscale) was determined from the extended theory, and was consistent with direct observation of slightly grown droplets. The growth mechanism of the ubmicrometer-sized droplets was also investigated; under this scale regime, the three-phase contact line does not recede during coalescence.

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