Comments on the Heidaryan–Jarrahian variant of the Redlich–Kwong equation of state

• Demonstration how an implicit equation of state can be used for the calculation of thermodynamic properties of a fluid.
• Demonstration of the effect of a logarithmic pressure dependence in an equation of state.
• Discussion of Brown's characteristic curves (so-called ideal curves).

The Heidaryan–Jarrahian variant of the Redlich–Kwong equation of state (RKHJ) for carbon dioxide is a cubic equation of state as far as the calculation of densities for given pressures and temperatures is concerned, but a complicated pressure-implicit equation with respect to the calculation of pressures for given densities and temperatures. In this work, it is shown that how the RKHJ equation can be used to calculate other properties than the density.The RKHJ equation is found to be applicable for supercritical temperatures only; it represents densities above 320 K well. It shows unphysical behavior at low densities because of a logarithmic pressure dependence of its attraction term.

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