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International Heat Transfer Conference 13

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

DRYOUT AND EVAPORATION HEAT TRANSFER OF FORCED CONVECTIVE FLOW IN A MINI-TUBE FOR AQUEOUS SLUTIONS WITH NONLINEAR SURFACE ENERGY

Naoki Ono
Department of Mechanical Engineering, Shibaura Institute of Technology, 3-7-5 Toyosu, Koto-ku, Tokyo 135-8548, Japan

T. H. Yen
Energy Technology Research Institute, National Institute of Advanced Industrial Science and Technology (AIST); and Nissan Motors Co., Ltd., 560-2, Okatsukoku, Atsugi, Kanagawa 243-0192, Japan

T. Yoshida
Department of Mechanical Engineering, Shibaura Institute of Technology, 3-7-5 Toyosu, Koto-ku, Tokyo 135-8548, Japan

Masahiro Shoji
Department of Mechanical Engineering, Kanagawa University, 3-27-1 Rokkakubashi, Kanagawa-ku, Yokohama, Kanagawa 221-8686; and Energy Technology Research Institute, AIST, 1-2-1 Namiki, Tsukuba, Ibaraki 305-8564, Japan

Fumio Takemura
Energy Technology Research Institute, AIST, 1-2-1 Namiki, Tsukuba, Ibaraki 305-8564, Japan

DOI: 10.1615/IHTC13.p12.270
12 pages

Abstrakt

Evaporation heat transfer of aqueous solution with nonlinear surface energy was experimentally investigated. Butanol aqueous solution was adopted as the test fluid. Different from most liquids, the direction of thermocapillary force in liquid film of nonlinear surface energy solution on a heated surface acts in the same direction to Marangoni force. Such thermocapillary and Marangoni effects could change the liquid motion and the evaporation heat transfer. The surface tension effects are expected to be marked in small-scale systems. However, there are not enough studies about the phase change heat transfer in micro or mini channel systems. The aim of the present study is to investigate the effect of the nonlinear surface tension of butanol aqueous solution on the liquid motion and heat transfer in convective boiling in single mini channel. The authors investigated the issue in comparison with pure water. The transparent quartz tube whose ID was 1 mm, coated with a very thin ITO/Ag film for Joule heating, was applied as the test mini-tube. The mass flux of the butanol solution in the tube was 1.96 kg/m2s, and that of pure water was 1.77 kg/m2s.
Prior to the experiments, the measurement of the surface tension about the butanol aqueous solution and pure water was performed by Wilhelmy's method to confirm the nonlinearity. From the surface tension measurement, the nonlinear temperature-dependency of the surface energy of 1-butanol aqueous solution (7.15 wt % at 20 Centigrade) was confirmed up to 93 Centigrade. From the convective boiling experiments in single mini-tube, it was found that the temperature of the outer surface of the tube was much lower in the case of the butanol aqueous solution at the region where the vapor quality was unity, than in the case of pure water. The local heat transfer coefficient defined in the present study was approximately 30 % smaller in the case of the butanol aqueous solution before the vapor quality reached unity, than in the case of pure water.
The liquid motions were observed by CCD video camera system, which revealed that smaller droplets were found and more area of dried inner surface of the tube existed in the case of the butanol aqueous solution than in the case of pure water. Moreover, in the case of the butanol aqueous solution some amounts of small separated droplets were found even at the region after the calculated vapor quality reached unity. The nonlinearity of the butanol aqueous solution can be thought to cause this remarkable characteristic in heat transfer and liquid motion.

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