The Latent Heat of Supercritical Fluids

Daniel Banuti

doi:10.3311/ppch.12871

Abstract

The article discusses the notion of a supercritical latent heat during 'pseudoboiling': Experimental, numerical, and theoretical evidence show that the supercritical state space is not homogeneous, but can be divided into liquid-like and gas-like domains, separated by an extension to the coexistence line -- the Widom line. The key concept are two limit states of ideal liquid and ideal gas, characterized by constant heat capacities, and analyze the transition between them. Then, analogous to subcritical vaporization, a supercritical state transition from liquid to gaseous overcomes intermolecular attractive forces, albeit over a finite temperature interval rather than at an equilibrium temperature. This distributed latent heat is in fact approximately invariant with respect to pressure for (0 < p < 3 pcr) and is thus valid at subcritical and supercritical conditions. This view also changes the perspective on subcritical latent heat: while it is an accurate representation of the required energy at very low pressures, the contribution of the distributed latent heat dominates the equilibrium latent heat as the critical pressure is approached.

Highlights

The supercritical state space has long been regarded as a continuous domain, in which the differences between liquids and gases vanish
The article discusses the notion of a supercritical latent heat during 'pseudoboiling': Experimental, numerical, and theoretical evidence show that the supercritical state space is not homogeneous, but can be divided into liquid-like and gas-like domains, separated by an extension to the coexistence line -- the Widom line
3 Conclusions An analysis of state transitions at subcritical and supercritical pressures showed that the enthalpy along isobars approaches ideal liquid and gaseous states, characterized by constant isobaric heat capacities

Summary

Introduction

The supercritical state space has long been regarded as a continuous domain, in which the differences between liquids and gases vanish. The state space of mixtures depends on the van Konynenburg and Scott [14] classification of the involved components [15]: Mixtures of similar fluids (Type I) exhibit a single common WL, while mixtures of dissimilar fluids (Type III) may develop several WL, corresponding to the mixture components

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Conclusion