Abstract
This paper presents a study of the natural circulation heat transfer to water flowing under supercritical pressures. Flow oscillations occurred when crossing the critical state, both from the compressed liquid region and from the supercritical vapour region. The threshold was found to correspond to the outlet film temperature, being close to the transposed critical value. Differential pressure fluctuations with frequencies of 25–60 Hz were encountered. These vibrations are generated in the heated section and propagate in the system when resonance occurs. The heat transfer data, when compared with available forced circulation correlations, showed the need for a new correlation having smaller exponents of Reynolds and Prandtl numbers. This was attributed to the power-dependence of flow rate.
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