Third-Order Gas-Liquid Phase Transition and the Nature of Andrews Critical Point

TL;DR

This paper investigates the nature of the Andrews critical point in gas-liquid transitions, proposing a dynamical model that reveals a third-order phase transition and explains observational challenges beyond this critical point.

Contribution

It introduces a dynamical model consistent with van der Waals near the critical point, revealing a third-order transition and extending the co-existence curve beyond Andrews point.

Findings

Andrews critical point is a switching point from first to third order transition

Gas-liquid co-existence curve extends beyond Andrews point

Transition beyond Andrews point is of third order

Abstract

The main objective of this article is to study the nature of the Andrews critical point in the gas-liquid transition in a physical-vapor transport (PVT) system. A dynamical model, consistent with the van der Waals equation near the Andrews critical point, is derived. With this model, we deduce two physical parameters, which interact exactly at the Andrews critical point, and which dictate the dynamic transition behavior near the Andrews critical point. In particular, it is shown that 1) the Andrews critical point is a switching point where the phase transition changes from the first order to the third order, 2) the gas-liquid co-existence curve can be extended beyond the Andrews critical point, and 3) the liquid-gas phase transition going beyond Andrews point is of the third order. This clearly explains why it is hard to observe the gas-liquid phase transition beyond the Andrews critical point. Furthermore, the analysis leads naturally the introduction of a general asymmetry principle of fluctuations and the preferred transition mechanism for a thermodynamic system.