Redlich–Kwong–Heidaryan–Jarrahian

Heidaryan and Jarrahian introduced a new temperature function into the Redlich–Kwong EOS which was specifically optimized for carbon dioxide. The new function depends not only on the reduced temperature, but also on the reduced pressure. The calculation of densities for given pressures and temperatures therefore remains an easy task (solving a cubic equation). The calculation of pressures for given densities and temperatures requires iterations, and the calculation of residual Helmholtz energies requires a combination of numerical and analytical integration, the latter involving the “exponential integral function”.

The equation should only be used for carbon dioxide. It yields good density data at supercritical conditions.

The EOS should not be used for *T* < *T*_{c},
as here the densities deviate much from the reference values. It
*cannot* be used at temperatures at which negative pressures
are possible. Caution is advised for small pressures: The EOS may
generate artifacts because a logarithmic pressure term in the
temperature function.

The critical compression factor of this EOS is fixed. It is not possible for this EOS to match all 3 critical conditions.

adjustable parameters: 0

[1] E. Heydarian, A. Jarrahian, *J. Supercrit. Fluids* 81 (2013)
92–98.

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