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International Heat Transfer Conference 15

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

Quantitative Estimation of Frost Formation on Plate-fin Tube Heat Exchanger by Neutron Radiography

Ryosuke Matsumoto
Department of Mechanical Systems Engineering Kansai University, 3-3-35 Yamate-cyo, Suita, Osaka 564-8680

Tomoya Yoshimura
Kansai University

Hisashi Umekawa
Department of Mechanical Engineering, Kansai University, 3-3-35 Yamate-cho, Suita-shi, Osaka 564-8680, Japan

Takeyuki Ami
Department of Mechanical Engineering, Kansai University, 3-3-35 Yamate-cho, Suita-shi, Osaka 564-8680, Japan

Daisuke Ito
Institute for Integrated Radiation and Nuclear Science, Kyoto University, 2, Asashiro-Nishi, Kumatori-cho, Osaka 590-0494, Japan

Yasushi Saito
Institute for Integrated Radiation and Nuclear Science, Kyoto University, 2, Asashiro-Nishi, Kumatori-cho, Osaka 590-0494, Japan

DOI: 10.1615/IHTC15.hex.009144
pages 3603-3615


KEY WORDS: Heat exchanger, Air conditioning and refrigeration, Frost, Neutron radiography, Mass transfer

Abstract

Frost formation on heat exchangers such as those used in refrigeration systems can have a serious impact on their heat transfer performance due to the thermal resistance of the frost layer. Many studies have been carried out to investigate frosting of heat exchangers, particularly with regard to the mass transfer coefficient. On the cooled surface of a heat exchanger, the frost grows with a spatial distribution that is determined by the temperature and humidity profiles of the air and the flow pattern in the heat exchanger. This means that the mass transfer coefficient for frost formation has both a temporal and spatial distribution. However, in conventional methods of measuring the frost deposition rate, the frost is scraped from the surface, making the distribution of its mass transfer coefficient difficult to determine. In the present study, the mass transfer characteristics of frost formation on a plate-fin tube heat exchanger were investigated using neutron radiography. Neutrons are strongly attenuated by the water molecules in the frost layer, but not by the aluminum heat exchanger material. The frost distribution can be quantitatively estimated based on neutron beam attenuation.The fin-tube heat exchanger consisted of five fins with a height of 28 mm and a width of 60 mm, together with two tubes with an outer diameter of 8.5 mm. The fin pitch was 10 mm. The heat exchanger was cooled by a refrigerant at -19 degrees C. Humid air at 6 degrees C and an absolute humidity of 0.004kg/kg' was introduced into the heat exchanger at an air velocity of 1.1 m/s. Frost formation and growth on the fin and tube surfaces could be clearly visualized by neutron radiography. The frost formed most rapidly on the fin and tube edges, and gradual growth was also observed in the wake region of the tube. The frost distribution was measured every 1 min, so that the local frost deposition rate could be estimated from differential images. In the early stages of frost formation, the highest mass transfer coefficient was found at the fin and tube edges. However, as time passed, it became uniform over the fins due to the increased thermal resistance of the frost. Thus, the spatial and temporal distributions of the local mass transfer coefficient could be successfully measured using neutron radiography.

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