Subcooled nucleate boiling heat transfer from a large diameter tube
- Atomic Energy of Canada Limited, Whiteshell, Manitoba (Canada). Whiteshell Labs.
- Ontario Hydro Nuclear, Toronto, Ontario (Canada)
- Ontario Hydro Technologies, Toronto, Ontario (Canada)
Nucleate boiling heat transfer from the outside of large-diameter tubes has not been well studied. There are many large-diameter horizontal tubes in the core of a CANDU{reg_sign} nuclear reactor, and it is important to quantify the different modes of heat transfer from the tubes (known as calandria tubes) to the heavy water moderator. This paper describes a series of experiments performed to study nucleate boiling heat transfer from the outside surface of a horizontal calandria tube to subcooled and pressurized light water. When the circulating pump was on, it caused an upflow of water in the vicinity of the tube, estimated to be an average of 0.3 m/s. The flow cooled the tube and increased the surface temperature fluctuations, in contrast to the relatively steady temperatures observed by Dowlati and Byrne (1995) in a test section of similar diameter, but made from a solid copper block. The cooling effect of the pumped flow was the greatest for high subcooling, low heat flux and high pressure. The magnitudes of these fluctuations are explained in terms of transient heat conduction when the surface alternates between nucleation and cooling by the cold liquid. The heat transfer from the bottom of the tube was modelled by a combination of pool boiling, global single-phase natural convection and stagnation-point single-phase forced-convection correlations. The experiments showed that Rohsenow`s pool boiling correlation (with a single-phase free convection component) successfully modelled the outer surface temperatures on the large-diameter horizontal tube when the circulating pump was off. Even at high water subcooling (60 C) and low heat flux (200 kW/m{sup 2}), nucleate boiling dominated the heat transfer.
- OSTI ID:
- 428075
- Report Number(s):
- CONF-960815--; ISBN 0-7918-1508-0
- Country of Publication:
- United States
- Language:
- English
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