Residual function, fugacity

The virial equation can not only describe the PvT behavior of gases, but also the different residual functions. Both forms (Leiden form and Berlin form) are well-suited for this purpose, but most of the thermodynamic functions can be derived easier using the Berlin form, because this form is volume explicit. Volume explicit means that the equation can be solved explicitly for vas a function of T and P. As an example, the calculations of the fugacity coefficient and of the residual function of the enthalpy are shown, using the virial equation in the Berlin form truncated after the second virial coefficient B. 

We noted in 13.2.3 that the fugacity coefficient, in the form RTXnjf, is a residual function, defined ( 13.2.3) as the difference between a real system thermodynamic function and the same function for an ideal gas under the same conditions. 

We should note that not only is a a residual function (Equation 8.8), but so in a closely related sense is the fugacity coefficient jf. We saw that the Gibbs energy for an ideal gas can be written = In P (Equation 8.1), and... 

Table 1. Compression factor, fugacity coefficient, and residual thermodynamic functions of real fluid Refrigerant 500...

In the present investigation, the compression factor, fugacity coefficient, and residual thermodynamic functions of the real fluid R-500 have been calculated using the BACK equation of state. For this purpose, the experimental data, i.e., critical constants, saturated liquid density, saturation vapor pressure, and the PVT data have been utilized. 

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