A Residual Entropy Scaling Approach for Viscosity Based on the GERG-2008 Equation of State

Abstract

A simple model for viscosity based on residual entropy scaling is proposed in this study. The thermodynamic model applied to calculate residual entropy is the Groupe Europeén de Recherches Gazieres (GERG) 2008 equation of state. Dimensionless pure-component viscosity as a function of residual entropy is correlated by a third-order polynomial. The component specific coefficients of the polynomial are adjusted to pure-component viscosity data. Averaged over all pure-component data points, deviation accounts to only 3.21%. Viscosity for mixtures is predicted by using the mole fraction weighted average of the purecomponent coefficients in the polynomial. Excellent results are obtained for natural gas mixtures. The averaged deviation for all 2021 evaluated natural gas data points is as low as 3.09%. Compared to alternative mixture viscosity models, this purely predictive approach is among the best performing models for most studied natural gas mixtures and sour gas samples. The proposed approach is not limited to natural gas viscosity, that is, methane-rich multi-component systems. Accurate predictions are also presented for binary and ternary mixtures over wide temperature and pressure ranges.

Dynamic Viscosity of Binary Fluid Mixtures: A Review Focusing on Asymmetric Mixtures

“…Subsequently, comprehensive studies on pure hydrocarbons were carried out by Bell [48,49]. First results for the calculation of viscosities in conjunction with Helmholtz-energy mixture equations of state were recently published by Binti Mohd Taib and Trusler [50], Mairhofer [51], and Yang et al [52]. With respect to the fluids investigated in the present work, Binti Mohd Taib and Trusler [50] only published parameters for the carbon dioxide + n-decane system.…”

“…This prerequisite is most important for the ECS model [18], since it is directly related to the corresponding states principle, which is known to work reliably only for similar fluids. The entropy scaling approaches [51,52] also have their limitations with respect to asymmetric mixtures [76]. In case of the friction theory [38], the same trend occurs, but it is less pronounced than for the other models.…”

“…However, this should be treated with caution. Recent density measurements [67,68] and a new mixture AARD / % ECS [18] sScale [51] FT [38] y=ethane Abe et al AARD / % ECS [18] sScale [51] FT [38] Overall AARD / % ECS [18] sScale [51] FT [38] Kestin and Yata [91] AARD / % ECS [18] sScale [51] FT [38] Bagzis [93] AARD / % ECS [18] sScale [51] FT […”

“…To clarify the situation, a more detailed analysis and refit of the thermodynamic mixture model is required. The phase equilibrium measurements Gozalpour et al [90] for the CO AARD / % ECS [18] sScale [51] sScale [52] FT [38] y=methane Davani et al AARD / % ECS [18] sScale [51] sScale [52] FT [38] y=propane Abe et al AARD / % ECS [18] sScale [51] sScale [52] FT [38] 20 (18) 310-404 Only liquid-phase viscosity data are considered because vapor data were not measured but calcuated model for calculating thermodynamic properties [69], in particular for liquefied natural gas mixtures, showed that trace elements can certainly have a significant impact depending on the location in the fluid state region. On the other hand, measurements become more challenging with increasing asymmetry of the binary system.…”

“…The representation of all binary mixture data by means of the ECS model [18], the two entropy scaling approaches [51,52], and the friction theory [38] is displayed as bar charts in Fig. 2.…”