Pseudo-boiling and concentration gradient in an enclosed supercritical binary mixture

Abstract

Recent publications have shown the effectiveness of the analogy between fluids at sub- and supercritical pressures and confirmed there is a distinguishable crossover between liquid-like and gas-like behavior in supercritical fluids. This work is devoted to extending such an analogy to miscible zeotropic binary mixtures, whose well-known feature in liquid-gas coexistence under a subcritical pressure is the concentration difference between liquid and gas. Due to the availability of thermophysical properties, C2H6−CO2 binary mixture is taken as a reference fluid. Through numerical simulations for the steady states of an enclosed binary mixture at supercritical pressures subjected to temperature differences, this paper reveals the coexistence of liquid-like and gas-like states is featured by a concentration gradient naturally established by the critically enhanced Soret effect. It suggests that the concentration gradient is enhanced as the critical pressure is approached or as the temperature difference is enlarged. Besides, the low heat-conducting nature of the gas-like state compared to the liquid-like one gives rise to a pressure drop. This work gives new insights into the similarities of binary mixtures under sub- and supercritical pressures. For the convenience of latter studies, an open-source code is provided to calculate the physical properties of C2H6−CO2 binary mixture.