Study of heat transfer to supercritical pressure water across a wide range of parameters in pulse heating experiments

Abstract

• Controlled pulse heating of supercritical pressure water was performed. • Unexpected response to the short-term release of high-power heat was revealed. • It is consistent with the character of the density change over supercritical isobars. • Reduced heat transfer coefficient exhibits a minimum at pseudocritical temperature. • We attribute this minimum to the suppression of fluctuations in short-term experiment. From experimental data on pulse heating of a thin wire probe in water pre-compressed to supercritical pressures at room temperature, the instantaneous heat transfer coefficient has been calculated over a wide temperature range from 250 °C to 700 °C. The pressure, being the parameter of the experiment, has been varied from the near-supercritical value (22.1 MPa) to 100 MPa. The heat flux density across the probe surface reached 10 MW/m 2 at a characteristic heating time of 20 ms. Under conditions of powerful heat release and small temporal and spatial scales, heat transfer is carried out mainly due to the heat conduction mode, which is the most physically determined mechanism of heat transfer. It has been revealed that the reduced heat transfer coefficient exhibits a minimum in the region of pseudocritical temperatures; this minimum becomes deeper, as the pressure value approaches the critical one. The obtained data can be useful in the design of heat exchange devices, the operation of which may include powerful local heat release, as well as in the simulation of emergencies associated with a sharp jump in reactivity in nuclear power units.