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ISSN Online: 2377-424X

ISBN Print: 978-1-56700-421-2

International Heat Transfer Conference 15
August, 10-15, 2014, Kyoto, Japan

Characteristics of Flow Boiling Heat Transfer in Rectangular Minichannels

Get access (open in a dialog) DOI: 10.1615/IHTC15.fbl.009589
pages 2667-2681

要約

The major mechanisms for vertical upward flow boiling heat transfer by R1234yf in rectangular multiport minichannels were investigated. The effect of surface tension becomes more significant than that of inertial forces in minichannels, which causes an unequal thickness distribution of the liquid film on the perimeter of rectangular channels. It is expected that better heat transfer performance can be obtained in rectangular minichannels because of evaporation of the thin liquid film on the center side of the channel surface. In this study, both visual observation of the flow pattern and experimental measurement of the heat transfer performance were conducted to reveal the flow boiling characteristics of the refrigerant inside rectangular minichannels with a hydraulic diameter of 0.9 mm, and the results were compared to those inside circular minichannels with a similar hydraulic diameter. The visual observation revealed that the liquid accumulated in the corners, and a thin liquid film existed on the flat surface; the liquid accumulation rate increased when the mass flux was small. In addition, unsteady dry patches were observed at higher heat fluxes. In addition, the measured heat transfer coefficient for the rectangular channels was much higher than that for the circular channels, especially under small mass flux and heat flux conditions. According to both the visual observation results and experimental measurement, it is evident that thin liquid film evaporation is the dominant heat transfer mechanism in rectangular minichannels. A lower mass flux leads to the formation of a thinner liquid film owing to surface tension, and a lower heat flux helps maintain the thin liquid film.