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NUMERICAL STUDY OF NATURAL CONVECTION IN A SINGLE-PHASE CLOSED TUBULAR THERMOSYPHON

DOI: 10.1615/ICHMT.2008.CHT.2090
10 pages

Isao Ishihara
Dept. of Mechanical Engineering, Kansai University, 3-3-35 Yamate-cho, Suita, Osaka 564-8680, JAPAN

Yasufumi Yamamoto
Department of Mechanical Engineering, Kansai University, Osaka, Japan

Abstrakt

As the heat transfer of the thermosyphon is greatly controlled by the fluid flow, it is important to clarify the flow characteristics. Present paper describes numerical predictions of the thermal and flow characteristics in the single-phase tubular thermosyphon, hich consists of three zones of an equal height; the upper and lower thirds of the surface are the zones of, respectively cooling and heating, the intermediate section being an adiabatic zone. The numerical simulation was performed by solving three dimensional unsteady governing equations and variable parameters are diameter of thermosyphon and the temperature difference between the heated and cooled surfaces. The numerical results showed that in case of a small temperature difference, a weak circulating flow takes place in each zone and with larger temperature difference, an impeded flow with branched flow appears in the intermediate zone, and the branched flow forms some pairs of the upward and downward flows and increases in number with increasing temperature difference or diameter. The experiment also was performed and the velocity distributions were measured by means of PIV (Particle Imaging Velocimetry) for combined conditions of diameter d, temperature difference ΔT and working fluid (silicone oil with different viscosity). A combination of d=34mm, ΔT=1.0K and viscosity of 10×10−5m2/s makes 1-pair of branched flow and 7-pair branched flow at the maximum appeared for d=46mm, ΔT=12.0K and viscosity of 2.0×10−5 m2/s. The numerical prediction is in very good agreement with these experimental results.

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