This equation was developed from the Peng–Robinson EOS by substituting a Twu temperature function for the Soave function and by using Peneloux' volume translation for improving the representation of liquid densities.
The amount of the volume translation is usually calculated from liquid volumes at 0.7 Tc, and it is temperature-independent. Consequently the EOS gives indeed better density results for many compounds. But the volume shift is usually not appropriate for the critical region. The critical compression factor is usually off, and it is not advisable to use the critical molar volume for parameter fitting.
adjustable parameters: 6
For mixture calculations the following mixing theories are available:
 J. Ahlers and J. Gmehling, Ind. Eng. Chem. Res. 41 (2002) 3489–3498.
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