5. Conclusions and discussion
The composition functionality of liquid and vapor mixture energy parameters given by the GHC equation of state were rigorously analyzed. It was shown that both expressions for the mixture energy parameter are quadratic, but non-symmetric, in composition under very reasonable approximations. For liquid mixtures, when ln(TcM) was replaced byC i=1 xiln(Tci), the resulting difference was small (<4%) and the corresponding sensitivity of aL M and L M over the entire binary composition range were <2% and <1% respectively for all mixtures studied. The maximum differences in aL M and L M were 3.15% and 1.79% for mixtures of CO2-water at 100 ◦C and 400 bar. In contrast, for vapor mixtures, the approximation of ˇM = (VM + bM)/VM by an average value, ˇ¯ M, provided rigorous, but weak, quadratic composition functionality of aV M. Moreover, this vapor approximation, ˇ¯ M, resulted in AAD% differences inaV M and V M of <10−3 and <10−4 respectively for all mixtures studied. Finally, although second virial coefficients predicted by the GHC equation exhibited weak quadratic composition functionality, this did not have an impact of vapor density predictions.
