Title High-Power Heat Release in Supercritical Water: Insight into the Heat Transfer Deterioration Problem

The investigation is focused on the phenomenon of heat transfer deterioration (HTD), inhibiting the use of supercritical fluids in the processes in which high-power local heat release is possible. The ordinary discussion is based solely on the data of quasi-stationary measurements. In order to clarify the intrinsic nature of HTD as an essentially non-stationary phenomenon, it is worthwhile to take into account the peculiarities of heat transfer confined in time and space. In the present paper, we briefly discuss the characteristic features of such heat transfer in supercritical water. The characteristic heating time was 10-3 divided by 10-2 10 and the heat flux density through the wall increased up to 15 MW/m2 The results provide the heat transfer pattern under conditions of predominance of the heat conduction mode. Exactly this mode most closely corresponds to the regime of high-power local heat release in a viscous sublayer. We also propose that the effect of threshold decrease in the heat transfer intensity (typical of pulse processes in supercritical transitions) may be a fundamental factor for occurrence of the HTD mode.