Heat transfer under high-power heat release: Not fully stable fluids as potential heat carriers

Abstract

• Significant disturbance in heat transfer under high-power heating was detected. • Supercritical-pressure water and highly unstable aqueous mixture were studied objects. • Heat transfer deterioration stage preceding macroscopic phase transition was revealed. • This stage is assumed to have universal character for fluid phase transitions. • Its nature is associated with the violation of homogeneity of not fully stable system. In this paper, we present new data on non-stationary heat transfer in sub- and supercritical liquids due to high-power heat release in a wire probe immersed in an investigated liquid. In the performed experiments, the characteristic heating time was from 5 to 180 ms, while the corresponding thickness of the heated layer was in the magnitude order of 10 1 µm. The impetus for the study came from the previous discovery of two unexpected effects. The first was a deterioration of heat transfer during the rapid transition of a compressed fluid to the supercritical region of temperatures along the isobar. The second was the distinctive character of the change in the heat flux density of a binary, partially miscible liquid when going deeper into the region of its unstable states. The study is aimed at clarifying the prospects of using supercritical fluids and mixtures with lower critical solution temperatures as potential heat carriers in processes where the possibility of powerful local heat release cannot be excluded.