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Conference Article: Heat transfer in the upper part of the HTTR pressure vessel during loss of forced cooling

Abstract

Heat transfer characteristics in upper part of pressure vessel of High Temperature Engineering Test Reactor (HTTR) during loss of forced cooling were studied experimentally by the use of hemispheres heated from below. Natural convection heat transfer and flow characteristics without thermal radiation were studied with several kinks of liquids as working fluids and thermo-sensitive liquid crystal powders as a visualization tracer. The ranges of Rayleigh and Prandtl numbers for the study were 10⁶ < Ra <5.5 x 10¹⁰ and 6 < Pr < 13000 for heat transfer experiment and 2 x 10⁵ < Ra < 1.9 x 10⁹ and 6 < Pr < 13000 for flow visualization experiment. Heat transfer correlations and flow characteristics were clarified in laminar and turbulent regions. In laminar region, circulating flow existed in a hemisphere, i.e., hot fluid risen up near the center of the hemisphere arrived at the top of the hemisphere and flowed downward along inner surface of hemisphere. Whereas, in turbulent region of Ra > 10⁹, the circulating flow disappeared and random upward and downward flow became dominant. Hot fluid released from the hot surface is dissipated immediately in surrounding fluid. Natural convection heat transfer experiment with thermal radiation is now also being carried. Maximum temperature of a hot surface can be raised up to 600 deg. C. Air is used as a working fluid. Rayleigh number range will be 1.5 x 10⁸ < Ra < 5.3 x 10⁸. Net heat transfer rate by natural convection can be obtained by subtracting the calculated heat transfer rate by thermal radiation. Estimated heat transfer rate by natural convection is compared with the results of natural convection experiment without thermal radiation.

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Reference:

Specialists meeting on decay heat removal and heat transfer under normal and accident conditions in gas cooled reactors. Juelich (Germany). 6-8 Jul 1992

International Atomic Energy Agency, Vienna (Austria)

IAEA-TECDOC--757, pp:125-130