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Journal of Enhanced Heat Transfer
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ISSN Druckformat: 1065-5131
ISSN Online: 1026-5511

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Journal of Enhanced Heat Transfer

DOI: 10.1615/JEnhHeatTransf.2012001693
pages 301-311

FALLING FILM EVAPORATION OF PURE REFRIGERANT HCFC123 IN A PLATE-FIN HEAT EXCHANGER

Junichi Ohara
Department of Ocean Mechanical Engineering, National Fisheries University, Nagatahonmachi 2-7-1, Shimonoseki, Yamaguchi, Japan
Shigeru Koyama
International Institute for Carbon-Neutral Energy Research (WPI-I2CNER), Kyushu University, 744 Motooka, Nishi-ku, Fukuoka 819-0395, Japan; Interdisciplinary Graduate School of Engineering Sciences, Kyushu University, Kasuga-koen 6-1, Kasuga-shi, Fukuoka 816-8580, Japan

ABSTRAKT

In the present study, the characteristics of heat transfer and flow patterns are investigated experimentally for the falling film evaporation of pure refrigerant HCFC123 in a vertical rectangular channel with a serrated-fin surface. The refrigerant liquid is supplied to the channel through 37 holes of a distributor. The liquid flowing down vertically is heated electrically from the rear wall of the channel and evaporated. To directly observe the flow patterns during the evaporation process, a transparent vinyl chloride resin plate is placed as the front wall. The experimental parameters are as follows: the mass velocity G = 28−70 kg/(m2·s), the heat flux q = 20−50 kW/m2, and the pressure P ≈ 100 kPa. It is clarified that the heat transfer coefficient α depends on G and q in the region of vapor quality x ≥ 0.3 while there is little influence of G and q in the region x ≤ 0.3. From the direct observation using a high-speed video camera and a digital still camera, flow patterns are classified into five typical patterns: plane liquid film, wavy liquid film, liquid film accompanied with a dry patch, liquid film accompanied with dripping, and liquid film accompanied with mist. Then the relation between heat transfer and flow pattern is clarified. The results of heat transfer characteristics are also compared with some previous correlation equations.


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