Effect of Pressure and Surface Wettability on Thermal Resistance across Solid–Liquid Interface in Supercritical Regime

Abstract

Micro-and nanoscale effects such as temperature jumps have a significant impact on heat transfer processes at the fluid−solid interface. Pressure is an important parameter for describing subcritical and supercritical fluids (SFs). However, with the wide application of the SFs heat transfer process in shale and deep geothermal systems, the effect of pressure on thermal resistance at the supercritical fluid−solid interface is unknown. In this study, the heat conduction process at the supercritical water−graphene interface is performed by molecular dynamics simulations. The effect of pressure on the interfacial thermal resistance under different surface wettabilities is investigated. The results show that the interfacial thermal resistance decreases with increasing pressure under all surface wettability. The effect of pressure becomes weaker as the surface wettability or pressure increases. The interfacial thermal resistance is determined by the peak density and structure factor of the first fluid layer and linearly related to the inverse of the product of the peak density and structure factor. The vibrational coupling of in-plane and out-of-plane phonon density of states is characterized by the structure factor and peak density, which represent the horizontal ordering mechanism and vertical layering mechanism of interfacial heat transfer, respectively. Moreover, the vertical layering mechanism is the main determinant of the interfacial thermal resistance. The mechanism of interfacial thermal resistance proposed in this study is verified for application to a wide range of wettability and supercritical water−copper interfaces. The lower interfacial thermal resistance of the supercritical water−copper interface results from the enhanced ordering of interfacial fluid represented by the horizontal mechanism. This study deepens the understanding of the mechanism of interfacial thermal resistance and is helpful for supercritical heat transfer at the micro-and nanoscale.

Critical Threshold for Bubble-like Nucleation during Pseudoboiling at Supercritical Pressures

“…During the pseudoboiling process, supercritical argon transitions from the LL phase to the GL phase, and the thermal conductivity decreases with the decrease in density, resulting in the suppression of the heat transfer. The decrease in fluid density also leads to a significant increase in thermal resistance at the fluid–solid interface . Heat transfer from the wall to the fluid as well as between the fluid and argon is inhibited, and the heat transfer rate is gradually reduced.…”

“…Figure shows that initial gas-like nuclei appear much later as the surface wettability decreases. The decrease in wettability leads to weak fluid–solid interaction and high interfacial thermal resistance, thus inhibiting the interfacial heat transfer. Similar to the analysis in Microscopic Mechanism of Supercritical Bubble-like Nucleation Section, the initial bubble-like nuclei occur when the total energy exceeds the threshold (Te > 0.012 eV at P = 8 MPa).…”