Modifying the Redlich-Kwong-Soave Equation of State

James H. McNeill, James E. Bidlack


The Redlich-Kwong-Soave equation of state for real gases and liquids has been modified in order to improve the match of calculated liquid molar volumes with measured data by allowing the b-parameter to be a function of the temperature and molar volume of real gases and liquids. Molecular dynamics simulations of the noble gas krypton, using the hard-sphere potential for a large number of krypton atoms, were performed to evaluate how the b-parameter varies with gas molar volume. The results of these simulations were applied when modifying the original Redlich-Kwong-Soave equation of state. In the modified Redlich-Kwong-Soave equation of state,
the a-parameter is kept constant. Also, in this modified version, the measured critical molar volume is employed as well as the measured critical temperature and critical pressure values in parameter determination at the critical point. From this determination of parameters for a number of real gases, the same parameters can be approximately calculated using the measured critical compressibility factor avoiding numerical procedures. This results in an equation of state that matches closely with the measured critical point for many gases as well as improving the match between the model and measured liquid molar volumes.

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