Study of Equilibrium Critical Phenomena in Fluid Argon

Author: Wu, Shyue Yuan

Year: 1972

Degree: Dissertation (Ph.D.)

Advisor: Pings, Cornelius J.

Committee Member: Unknown, Unknown

Option: Chemical Engineering

DOI: 10.7907/Z20H-HM70

Abstract

The refractive index of fluid argon was measured by using the method of angle of minimum deviation for λNa = 5893Å. The measurements were carried out along the coexistence curve and along fourteen single phase isotherms from 150.7° to 163°K at pressures from 40 to 90 atmospheres.

The Lorentz-Lorenz relation was used to relate the refractive index data to the densities and subsequently to find the isothermal compressibilities along the singla phase isotherms. Following the law of rectilinear diameter and the simple power laws for critical exponents, the values of the critical temperature and exponents for argon were found to be Tc = 150.725° ± 0.010°K, β = 0.3574 ± 0.0027, and γ = 1.170 ± 0.013. Also values of nc = 1.08611 and Pc = 47.983 atm were determined. These values agree well with others reported for argon. Comparison of the values of β and γ with those predicted by the classical theory and the three-dimensional lattice gas model suggests that the latter gives a better description of the critical behavior of fluid argon.

Analysis of the reduced chemical potential differences, computed from the refractive index data along the singla phase isotherms, has been made by using the scaled equation of state first proposed by Widom. Reasonable values Tc and γ were obtained when the value of β determined above was used.

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