Estimating metastable thermodynamic properties by isochoric extrapolation from stable states

Area of Science:

• Thermodynamics
• Statistical Mechanics
• Fluid Dynamics

Background:

• Describing metastable fluids, which are in local but not global equilibrium, is critical for thermodynamics and industrial applications, especially first-order phase transitions.
• Current methods often rely on isothermal extrapolation from stable states, using virial expansions for gases or density expansions for liquids.

Purpose of the Study:

• To investigate the efficacy of isochoric (constant volume) pressure extrapolation as a superior alternative to isothermal density extrapolation for metastable fluids.
• To develop and evaluate isochoric extrapolation strategies for both vapor and liquid phases and a direct simulation method for expansion coefficients.

Main Methods:

• Developed and evaluated two distinct isochoric extrapolation strategies, one for vapors and one for liquids.
• Presented a method for directly calculating isochoric expansion coefficients from canonical ensemble simulations.
• Validated methods using the van der Waals equation of state and Lennard-Jones potentials.

Main Results:

• Isochoric extrapolation proved superior to isothermal density expansion for predicting metastable fluid properties.
• Methods accurately reproduced simulation results for Lennard-Jones potentials and predicted deeply metastable pressures even from high temperatures.
• Isochoric extrapolation successfully predicted the thermodynamic spinodal (mechanical stability limit).

Conclusions:

• Isochoric pressure extrapolation is an effective and accurate method for determining metastable fluid properties and phase transition boundaries.
• The approach accurately predicts spinodal curves, offering a more reliable alternative to existing methods, as demonstrated by water's predicted spinodal behavior.