Interfacial ordering reverses the boiling curve in supercritical fluids

Abstract

Heat transfer in supercritical fluids is commonly interpreted as single-phase convection, where heat fluxes vary monotonically with wall superheat. In this work, a counterintuitive phenomenon, i.e., the heat fluxes increase with decreasing wall temperatures, usually termed “boiling curve reversion” in subcritical conditions, is observed on a heated wire in a supercritical fluid. Our measurements reveal that the inversion is governed by the periodic formation, lateral chain-like diffusion, and collapse of vapor-like column clusters near the heated wall. These structures separate vapor-like (VL) and liquid-like (LL) pathways and drive ordered sweeping of low-temperature, high-density fluid toward the heated surface, thereby enhancing transient heat transfer. To quantify this process, an ordered cooling intensity S is defined from the total VL–LL interfacial area and is found to correlate negatively with wall temperature. A chain-diffusion model further indicates that zero-surface-tension interfacial instability underlies the evolution of the column clusters and the resulting heat-transfer enhancement. The above results support the conclusion that self-organized interfacial ordering underlies heat-transfer-curve inversion in supercritical fluids. Our findings offer clear evidence for the two-phase nature of supercritical fluids in terms of heat transfer, providing a new framework for understanding the negative “boiling curve” in fluids with vanishing surface tension.