Controlled high-power heat release as a tool to selecting working pressure for supercritical water

Resumo

The specificity of nonsteady heat conduction in water in the course of its rapid isobaric transition from the state of compressed liquid to supercritical state was studied by the method of controlled pulse heating of a thin wire probe immersed in the substance under investigation. The characteristic pulse length was of the order of milliseconds, the thickness of heating layer appeared to be of the order of micrometers, the density of heat flux from the probe into the substance was 10MW/m² by the order of magnitude. Based on the results of our experiments, we have developed a phenomenological approach to selecting the way for further research of heat transfer in supercritical fluids, in order to reach guaranteed removal of the heat fluxes with high densities. Namely, taking into account the revealed phenomenon of threshold decrease in heat transfer intensity, which is higher, the closer the value of the pressure is to the critical one, there is a reason for selecting much higher values of working pressure. The corresponding choice should be made in the range of 2.0... 3.0 p_c. We can point out such benefits of this choice (in terms of thermophysics) as the decrease in thermal resistance of the boundary layer, the enhancement in water thermal effusivity and its relatively weak dependence on pressure.