A generalized model for the thermodynamic properties of mixtures

A mixture model explicit in Helmholtz energy has been developed which is ca pable of predicting thermodynamic properties of mixtures containing nitroge n, argon, oxygen, carbon dioxide, methane, ethane, propane, n-butane, i-but ane, R-32, R-125, R-134a, and R-152a within the estimated accuracy of avail able experimental data. The Helmholtz energy of the mixture is the sum of t he 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 t his work. The independent variables are the density, temperature, and compo sition. 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 is +/- 0.2% in density, +/-0.1% in the speed of sound at pressures below 10 MPa, /-0.5% in the speed of sound for pressures above 10 MPa, and +/-1% in heat capacities. In the region from 250 to 350 K at pressures up to 30 MPa, calc ulated densities are within +/-0.1% for most gaseous phase mixtures. For bi nary mixtures where the critical point temperatures of the pure fluid const ituents are within 100K of each other, calculated bubble point pressures ar e generally accurate to within +/- 1 to 2%. For mixtures with critical poin ts further apart, calculated bubble point pressures are generally accurate to within +/-5 to 10%.