Thermodynamic properties of mixtures of nitrogen, argon, and oxygen, including air

A mixture model explicit in Helmholtz energy has been developed which is capable of predicting the thermodynamic properties of mixtures containing nitrogen, argon, and oxygen, including air. The calculation for air assumes a ternary mixture of these three components and neglects the presence of water vapor, carbon dioxide and trace elements known to be present in atmospheric air. The Helmholtz energy of the mixture is the sum of the ideal gas contribution, the residual contribution, and the contribution from mixing. The contribution from mixing is given by a single generalized equation which is applied to all mixtures used in this work. The independent variables are the reduced density and reduced temperature. The model may be used to calculate thermodynamic properties of mixtures at various compositions including dew and bubble point properties and critical points. It incorporates the most accurate published equation of state for each pure fluid. The model may be used to calculate the properties of mixtures generally within the experimental accuracies of the available measured properties. The estimated accuracy of calculated properties is +/-0.1% in density, +/-0.5% in the speed of sound, and +/-1% in heat capacities. Calculated bubble point pressures are generally accurate to within +/-1%.