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Alpha functions of Soave-Redlich-Kwong(SRK)equation of state proposed by Soave,Twu,and Luowere different in mathematic tendency.They were compared in modeling methane-alkanes equilibria with van derWaals mixing rule and Modified Huron-Vidal(MHV1)mixing rule,respectively.Results showed that Luo’s alphafunction was a little more accurate than Soave’s,and Twu’s alpha function lacked accuracy in modeling meth-ane-alkanes equilibrium.SRK equation of state was expanded as virial form,and then the equivalent terms werecontrasted with terms of virial equation of state.Results showed that Soave’s and Luo’s alpha functions matched thetendency of virial coefficient better than Twu’s,and Luo’s alpha function matched better than Soave’s in wide tem-perature range,which sustained the conclusions of phase equilibria calculation.Luo’s alpha function keeps de-creasing when Tr>1 and becomes negative at sufficient high temperature,thus the conventional cubic equation ofstate expressed pressure as the sum of repulsion pressure pR(>0),and attraction pressure pA(<0)could be im-proved to be the sum of hard-sphere repulsion pressure pH(>0)and intermolecular force pressure pI(pI<0 at lowtemperature and pI>0 at sufficient high temperature).
Alpha functions of Soave-Redlich-Kwong (SRK) equation of state proposed by Soave, Twu, and Luowere different in mathematic tendency. They were compared in modeling methane-alkanes equilibria with van der Waals mixing rule and Modified Huron-Vidal (MHV1) mixing rule, respectively. Results showed that Luo’s alphafunction was a little more accurate than Soave’s, and Twu’s alpha function lacked accuracy in modeling meth-ane-alkanes equilibrium. SRK equation of state was expanded as virial form, and then the equivalent terms werecontrasted with terms of virial equation of state. Results showed that Soave’s and Luo’s alpha functions matched thetendency of virial coefficient better than Twu’s, and Luo’s alpha function matched better than Soave’s in wide tem-perature range, which sustained the conclusions of phase equilibria calculation. Luo’s alpha function keeps de-creasing when Tr> 1 and becomes negative at sufficient high temperature, thus the conventional cubic equation of state is expressed p ressure as the sum of repulsion pressure pR (> 0), and attraction pressure pA (<0) could be im-proved to be the sum of hard-sphere repulsion pressure pH (> 0) and intermolecular force pressure pI at low temperature and pI> 0 at sufficient high temperature.