Communication: Ab initio Joule-Thomson inversion data for argon.

Area of Science:

• Thermodynamics
• Physical Chemistry
• Computational Physics

Background:

• The Joule-Thomson coefficient is a key thermodynamic property describing temperature changes in an ideal gas undergoing isenthalpic expansion.
• Accurate calculation of this coefficient is essential for understanding gas behavior under various conditions, particularly near phase transitions.
• Existing models often struggle to accurately represent experimental data in low-temperature and low-pressure regimes.

Purpose of the Study:

• To compute the Joule-Thomson coefficient (μ(H)(P, T)) for argon.
• To utilize an accurate virial equation of state, extended up to the seventh order.
• To assess the impact of higher-order virial coefficients on predicting gas behavior, especially in challenging thermodynamic regions.

Main Methods:

• Employing a seventh-order virial equation of state.
• Utilizing accurate ab initio data for argon.
• Calculating the Joule-Thomson coefficient as a function of pressure (P) and temperature (T).

Main Results:

• Higher-order virial corrections are critical for accurately fitting low-temperature and low-pressure data.
• The calculated Joule-Thomson inversion curve shows improved behavior, avoiding premature divergence.
• Good agreement with experimental data was achieved for temperatures above 250 K.

Conclusions:

• The seventh-order virial equation of state, derived from ab initio data, provides accurate predictions for argon's Joule-Thomson coefficient at higher temperatures.
• The study highlights the necessity of incorporating higher-order terms to capture complex gas behavior in specific thermodynamic regimes.
• Limitations of the virial equation become apparent near the critical temperature, indicating the need for alternative models in such regions.