On the definition of the components’ difference in properties in the unified extrapolation model

As an important method to link the thermodynamic properties of a binary system to that of a multicomponent system, many extrapolation models have been proposed in the past. However, lacking clear rules to distinguish the applicable systems of these extrapolation models led to much confusion during choosing a concrete model. Recently, a unified extrapolation model has been proposed by introducing a contribution coefficient, which is correlated to the difference in properties between the third component and a component from the selected sub-binary system. In this paper, two ways to treat this difference were discussed and their performances were tested by predicting the integral enthalpy of mixing in multicomponent systems. The results showed that when the properties difference is confined to the considered two components, the predicted values are in perfect agreement with the experimental data both in symmetric systems and in asymmetric systems; when this difference is defined by considering the interaction of the two components with the other one from the sub-binary system, the obtained results are in good agreement with the experimental data only in the symmetric systems. The reason is in the latter consideration, the treatment may exaggerate the properties difference in components.