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Dimensionless analysis of bubble departure frequency in forced convective subcooled boiling flow

Situ, Rong, Tu, Jiyuan , Yeoh, Guan Heng , Hibiki, Takashi , Ishii, Mamoru , & Mori, Michitsugu (2007) Dimensionless analysis of bubble departure frequency in forced convective subcooled boiling flow. In Ito, Takahiko, Hassan, Yassin, Kang, Rixin, & Stoll, Uwe (Eds.) 15th International Conference on Nuclear Engineering, 22-26 April 2007, Nagoya, Japan.

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Abstract

The capability to predict two-phase flow behaviours in forced convective subcooled boiling flow is of considerable interest to boiling water reactor safety. Currently, the two-fluid model together with the interfacial area transport equation or population balance approach can potentially offer an advanced and accurate analysis of thermal-hydraulic characteristics for nuclear reactor systems. Furthermore, for applications to subcooled boiling conditions, several parameters such as nucleation number density, bubble departure size and bubble departure frequency are required as necessary boundary conditions to the models. The ebullition cycle, i.e., the reciprocal of the bubble departure frequency, consists of the bubble waiting and growth periods: bubble waiting period begins from the departure of the last bubble from the nucleation site and ends at the moment the current bubble radius reaches the wall cavity radius; and the bubble growth period lasts from the end of the bubble waiting period to the bubble departure. Data on bubble departure frequency are in abundance in literature for pool boiling. For forced convective subcooled boiling flow, bubble departure frequency data are, however, rather limited.

Forced convective subcooled boiling experiments were conducted in a vertical-upward annular channel by using water as the testing fluid at atmosphere pressure. The test runs comprised of inlet temperatures, velocities and wall heat fluxes ranging from 80.0C to 98.5C, 0.5 m/s to 1.0 m/s and 62.0 kW/m2 to 205.5 kW/m2 respectively. A high-speed digital video camera was employed to capture the bubble departure frequencies for a total of 75 test conditions. Experimental observation showed that if the liquid subcooling was high, quenching occurred with the apparent bubble waiting period occupying a major part of the ebullition cycle. However, when the liquid subcooling was low, the waiting period was found to be negligible thereby yielding a high departure bubble frequency. Existing models/correlations on bubble waiting time, growth time, and departure frequency were reviewed and compared with the current experimental data and datasets available in literature. The correlations developed from pool boiling do not work well for forced convective boiling flow, and the models proposed for subcooled boiling flow cannot predict the bubble departure frequency in wide experimental range. Important dimensionless numbers were deduced from the available models/correlations. The non-dimensional bubble departure frequency was correlated with dimensionless heat flux, and the latter was fitted with the square power of Jacob number. The proposed correlation agreed reasonably well with the experimental data.

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ID Code: 10307
Item Type: Conference Paper
Additional Information: For more information, please refer to the journal’s website (see hypertext link) or contact the author.
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Keywords: Bubble departure frequency, subcooled boiling, forced convection, and bubble departure size
Subjects: Australian and New Zealand Standard Research Classification > ENGINEERING (090000) > MECHANICAL ENGINEERING (091300) > Mechanical Engineering not elsewhere classified (091399)
Australian and New Zealand Standard Research Classification > ENGINEERING (090000) > INTERDISCIPLINARY ENGINEERING (091500) > Heat and Mass Transfer Operations (091505)
Divisions: Past > QUT Faculties & Divisions > Faculty of Built Environment and Engineering
Past > Institutes > Institute for Creative Industries and Innovation
Copyright Owner: Copyright 2007 Japan Society of Mechanical Engineers
Deposited On: 23 Oct 2007
Last Modified: 29 Feb 2012 23:38

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