Abstract
The thermodynamic behavior of the simple binary mixtures in the vicinity of critical line has a universal character and can be mapped from pure components using the isomorphism hypothesis. Consequently, based upon the principle of isomorphism, critical phenomena and similarity between P-ρ-T and T-η-(viscosity)-P relationships, the viscosity model has been developed adopting two cubic, Soave-Redlich-Kwong (SRK) and Peng-Robinson (PR), equations of state (EsoS) for predicting the viscosity of the binary mixtures. This procedure has been applied to the methane-butane mixture and predicted its viscosity data. Reasonable agreement with the experimental data has been observed. In conclusion, we have shown that the isomorphism principle in conjunction with the mapped viscosity EoS suggests a reliable model for calculating the viscosity of mixture of hydrocarbons over a wide pressure range up to 35 MPa within the stated experimental errors.
Highlights
Accurate prediction of the critical properties and evaluation of the phase behavior of pure substances and mixtures are the basis for developing and improving equations of state (EsoS)
The primary and simplest extension on the construction of EsoS is done starting from van der Waals, Berthelot, and Dieterici EsoS.[1]
Thereafter, for fluid mixtures a scaled EoS was proposed for analyzing the asymmetric fluid-phase behavior asymptotically close to the critical point using the principle of isomorphism.[9,10]
Summary
In this work, using the critical isomorphism principle, the thermodynamical free energy of two SRK and PR EsoS was derived for binary fluid mixtures. The reason for choosing classical SRK and PR EsoS was the capability the former for fitting the experimental data and predicting the phase behavior of mixtures in the critical regions and that of the latter for accurately predicting the vapor-liquid equilibrium of the pure substances and equilibrium ratios of the components in the mixtures. In Sec.[3] we describe the specific procedure adopted for mapping the thermodynamic surface of the mixtures to that of onecomponent fluids following the ideas of Griffiths and Wheeler[27] and Leung and Griffiths[5] and formulate a corresponding isomorphic Helmholtz free energy for prediction the viscosity of fluid mixtures.
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