A formulation developed previously for the prediction of the thermodynamic properties of single-phase states of binary and ternary mixtures in the nitrogen-argon-oxygen system has been revised to include the calculation of vapor-liquid equilibrium IVLEJ properties. The model is based on the theory of extended corresponding states with wm der Waals mixing rules. Binary interaction parameters have been determined with single-phase P-p-T and vaporliquid equilibrium data to improve the accuracy of thermodynamic property predictions. The model accurately represents single-phase and vapor-liquid equilibrium properties over a wide range of compositions for binary and ternary mixtures. Comparisons of calculated properties to selected mixture data for both single-phase and VLE states are included.KEY WORDS: binary interaction parameters: extended corresponding states: shape factors: single-phase P-p-T; vapor-liquid equilibrium.
!. INTRODUCTIONThe need for an accurate wide-range model for predicting thermodynamic properties of fluid mixtures has been well established. Because there is a significant quantity of measured property data for binary and ternary mixtures of nitrogen, argon, and oxygen, these systems may be used for testing methods of property calculation.
EXTENDED CORRESPONDING-STATES (ECS) MODEL FOR MIXTURESThe equations of state used in this work for calculation of pure-fluid properties are those of Jacobsen et al. [5] for nitrogen, Schmidt and Wagner [6] for oxygen, and Stewart and Jacobsen [7] for argon. The model used in this research is described in detail by Clarke where ~ is the residual Helmholtz energy, Z is the compressibility factor, 6 = (p/p~)is the reduced density, r = (TJT)is the reciprocal reduced temperature, the subscript c indicates a critical property, the subscript o refers to the reference fluid, and the subscript m refers to the mixture. The symbols ~,, and 0.,, are shape factors which are used to relate the reduced properties of the mixture to those of the reference fluid. The thermodynamic properties for the mixture are reduced by the parameters, p .... and T~ .... which are given by t,c., = ZZ j ~. xt, x,, T~t,,,/pcp,, P q Tern :Z Z p q where p and q are indices which refer to different mixture components.
Corresponding States for Properties of Nz-Ar-O z Mixtures
1291In Eqs. (3) and (4) The shape factors ¢., and 0., for the mixture are given byP qOn,= Z ~.\ ',,.\',,Ol,,,;[~;,,! (8)
P qThe combining rules for the calculation of ¢,,,, and 0,,,, are given by ~1;,,1 = at,q + --( 11 ) T m dp,, ~r,, = ce,, 4---
