A generalized model for the thermodynamic properties of mixtures

• Published in: International journal of thermophysics 1999-05, Vol.20 (3), p.825-835
• Main Authors: LEMMON, E. W, JACOBSEN, R. T
• Format: Article
• Language: English
• Subjects: Applied sciences; ARGON; CARBON DIOXIDE; Compressibility of liquids; Cryogenic liquids; Cryogenics; Energy; ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATION; Energy. Thermal use of fuels; EQUATIONS OF STATE; Exact sciences and technology; Free energy; HYDROCARBONS; MATERIAL SUBSTITUTION; MATHEMATICAL MODELS; Mixing; MIXTURES; NITROGEN; OXYGEN; REFRIGERANTS; Refrigerating engineering; Refrigerating engineering. Cryogenics. Food conservation; THERMODYNAMIC PROPERTIES
• ISSN: 0195-928X; 1572-9567
• DOI: 10.1023/A:1022627001338

A mixture model explicit in Helmholtz energy has been developed which is capable of predicting thermodynamic properties of mixtures containing nitrogen, argon, oxygen, carbon dioxide, methane, ethane, propane, n-butane, i-butane, R-32, R-125, R-134a, and R-152a within the estimated accuracy of available experimental data. The Helmholtz energy of the mixture is the sum of the ideal gas contribution, the compressibility (or real gas) contribution, and the contribution from mixing. The contribution from mixing is given by a single generalized equation which is applied to all mixtures studied in this work. The independent variables are the density, temperature, and composition. The model may be used to calculate the thermodynamic properties of mixtures at various compositions including dew and bubble point properties and critical points. It incorporates accurate published equations of state for each pure fluid. The estimated accuracy of calculated properties if plus or minus 0.2% in density, plus or minus 0.1% in the speed of sound at pressures below 10 MPa, plus or minus 0.5% in the speed of sound for pressures above 10 MPa, and plus or minus 1% in heat capacities. In the region from 250 to 350 K at pressures up to 30 MPa, calculated densities are within plus or minus 0.1% for most gaseous phase mixtures. For binary mixtures where the critical point temperatures of the pure fluid constituents are within 100 K of each other, calculated bubble point pressures are generally accurate to within plus or minus 1 to 2%. For mixtures with critical points further apart, calculated bubble point pressures are generally accurate to within plus or minus 5 to 10%.