Analysis and Comparison of the Alpha Functions of SRK Equation of State

Abstract

Abstract: Alpha functions of Soave-Redlich-Kwong(SRK)equation of state proposed by Soave,Twu,and Luo were 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 alpha function was a little more accurate than Soave's,and Twu's alpha function lacked accuracy in modeling methane-alkanes equilibrium.SRK equation of state was expanded as virial form,and then the equivalent terms were contrasted with terms of virial equation of state.Results showed that Soave's and Luo's alpha functions matched the tendency of virial coefficient better than Twu's,and Luo's alpha function matched better than Soave's in wide temperature range,which sustained the conclusions of phase equilibria calculation.Luo's alpha function keeps decreasing when T_r>1 and becomes negative at sufficient high temperature,thus the conventional cubic equation of state expressed pressure as the sum of repulsion pressure p_R(>0),and attraction pressure p_A(<0)could be improved to be the sum of hard-sphere repulsion pressure p_H(>0)and intermolecular force pressure pI(pI<0 at low temperature and p_I>0 at sufficient high temperature).

Key words: equation of state, virial coefficient, phase equilibria, intermolecular force

摘要： Alpha functions of Soave-Redlich-Kwong(SRK)equation of state proposed by Soave,Twu,and Luo were 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 alpha function was a little more accurate than Soave's,and Twu's alpha function lacked accuracy in modeling methane-alkanes equilibrium.SRK equation of state was expanded as virial form,and then the equivalent terms were contrasted with terms of virial equation of state.Results showed that Soave's and Luo's alpha functions matched the tendency of virial coefficient better than Twu's,and Luo's alpha function matched better than Soave's in wide temperature range,which sustained the conclusions of phase equilibria calculation.Luo's alpha function keeps decreasing when T_r>1 and becomes negative at sufficient high temperature,thus the conventional cubic equation of state expressed pressure as the sum of repulsion pressure p_R(>0),and attraction pressure p_A(<0)could be improved to be the sum of hard-sphere repulsion pressure p_H(>0)and intermolecular force pressure pI(pI<0 at low temperature and p_I>0 at sufficient high temperature).

关键词: equation of state, virial coefficient, phase equilibria, intermolecular force

LUO Mingjian, HU Bing, JIANG Tao, XIA Shuqian, MA Peisheng. Analysis and Comparison of the Alpha Functions of SRK Equation of State[J]. , 2008, 16(5): 766-771.

罗明检, 胡冰, 姜涛, 夏淑倩, 马沛生. Analysis and Comparison of the Alpha Functions of SRK Equation of State[J]. , 2008, 16(5): 766-771.

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