A Theoretical Analysis on Enthalpy of Vaporization: Temperature-Dependence and Singularity at the Critical State

TL;DR

This paper presents a rigorous, parameter-free formula for the temperature-dependent enthalpy of vaporization, accurately predicting its variation up to the critical point and addressing the lack of a universal theoretical framework.

Contribution

It derives a first-principles-based composite formula for vaporization enthalpy that is system-independent and valid across the entire temperature range up to the critical point.

Findings

The formula accurately predicts vaporization enthalpy from reference to critical temperature.

It reveals a singularity at the critical state.

The approach eliminates the need for system-dependent fitting parameters.

Abstract

Accurate evaluation of enthalpy of vaporization (or latent heat of vaporization) and its variation with temperature is of great interest in practical applications, especially for combustion of liquid fuels. Currently, a theoretically rigorous formulation for latent heat is still not in place; and the existing fitting formulas for various fluids are, in nature, system-dependent. In this paper, the enthalpy of vaporization and its change with temperature are derived rigorously from first principles at the reference and critical states. A composite formula for enthalpy of vaporization is constituted from physical plausibility. The composite formula contains no fitting parameters; and it can accurately predict the enthalpy of vaporization from the reference temperature to the critical temperature.