A visual study of water subcooled flow boiling was conducted to clarify the mechanism of triggering the net vapor generation (NVG). The test section was a transparent sapphire grass tube of 20 mm in inside diameter; a high-speed camera was used to capture the behavior of vapor bubbles. In the present experiments, the vapor void fraction in the heated tube was expressed as the function of the following bubble parameters: nucleation site density, frequency of bubble release, bubble lifetime, and bubble size. Among these four bubble parameters, the bubble size had a particularly strong influence on the vapor void fraction: the void fraction was approximately proportional to the forth power of mean bubble diameter. Consequently, mean bubble diameter should be large enough for the vapor void fraction to increase rapidly with the wall heat flux. In low flowrate experiments, bubbles generated at nucleation sites were relatively large at the onset of nucleate boiling (ONB). The heat flux at ONB hence appeared the reasonable approximation of that at NVG. Whereas, in high flowrate experiments, bubbles were small at ONB and much higher heat flux was necessary to obtain large bubbles. Thus, the heat flux required to trigger NVG was much higher than that at ONB. It was concluded in the present experimental conditions that accurate evaluation of mean bubble diameter was of significant importance in predicting the onset of net vapor generation.
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14th International Conference on Nuclear Engineering
July 17–20, 2006
Miami, Florida, USA
Conference Sponsors:
- Nuclear Engineering Division
ISBN:
0-7918-4245-2
PROCEEDINGS PAPER
Dependence of Vapor Void Fraction on Fundamental Bubble Parameters in Subcooled Flow Boiling
Hayato Kubota,
Hayato Kubota
Osaka University, Suita-shi, Osaka, Japan
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Tatsuhiro Ishida,
Tatsuhiro Ishida
Osaka University, Suita-shi, Osaka, Japan
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Tomio Okawa,
Tomio Okawa
Osaka University, Suita-shi, Osaka, Japan
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Isao Kataoka,
Isao Kataoka
Osaka University, Suita-shi, Osaka, Japan
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Michitsugu Mori
Michitsugu Mori
Tokyo Electric Power Company, Yokohama, Japan
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Hayato Kubota
Osaka University, Suita-shi, Osaka, Japan
Tatsuhiro Ishida
Osaka University, Suita-shi, Osaka, Japan
Tomio Okawa
Osaka University, Suita-shi, Osaka, Japan
Isao Kataoka
Osaka University, Suita-shi, Osaka, Japan
Michitsugu Mori
Tokyo Electric Power Company, Yokohama, Japan
Paper No:
ICONE14-89208, pp. 537-545; 9 pages
Published Online:
September 17, 2008
Citation
Kubota, H, Ishida, T, Okawa, T, Kataoka, I, & Mori, M. "Dependence of Vapor Void Fraction on Fundamental Bubble Parameters in Subcooled Flow Boiling." Proceedings of the 14th International Conference on Nuclear Engineering. Volume 4: Computational Fluid Dynamics, Neutronics Methods and Coupled Codes; Student Paper Competition. Miami, Florida, USA. July 17–20, 2006. pp. 537-545. ASME. https://doi.org/10.1115/ICONE14-89208
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