Between supercritical liquids and gases - Reconciling dynamic and thermodynamic state transitions

被引:53
作者
Banuti, D. T. [1 ]
Raju, M. [2 ]
Ihme, M. [2 ]
机构
[1] Univ New Mexico, Albuquerque, NM 87131 USA
[2] Stanford Univ, Dept Mech Engn, Stanford, CA 94305 USA
关键词
Widom line; Frenkel line; Higher order phase transition; Pseudo boiling; WIDOM LINE; CO2; FLUIDS; BEHAVIOR;
D O I
10.1016/j.supflu.2020.104895
中图分类号
O64 [物理化学(理论化学)、化学物理学];
学科分类号
070304 ; 081704 ;
摘要
Experimental, computational, and theoretical results have shown that the notion of a homogeneous supercritical state space has to be replaced with distinct liquid-like and gas-like regions, divided by a cross-over line. Several such cross-over lines have been proposed, such as the Frenkel line, the Fisher-Widom line, and the Widom line. We use thermodynamics arguments, molecular dynamics (MD) simulations, and experimental data to investigate the relation between these lines. This work proposes a new interpretation of the Widom line based on the curvature of the Gibbs free energy, showing that the supercritical cross-over can be evaluated as a projection of the subcritical phase transition from a liquid to an ideal gas state to supercritical conditions. We show that the cross-over across the Widom line should not be regarded as instantaneous, but instead as spreading over a finite temperature interval. The thermodynamic character of the Widom line becomes negligible at reduced pressures p/p(cr) >3 and disappears completely at higher pressures p/p(cr) > 10. We find evidence that measured transitions attributed to the Widom line do in fact match the Frenkel line better. In this way, we suggest a consistent view of the supercritical state space and resolve apparent contradictions. (C) 2020 Elsevier B.V. All rights reserved.
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页数:6
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