A Thermodynamic Property Model for the R-134a/245fa Mixture

A thermodynamic property model explicit in the Helmholtz energy is presented for the R-134a/245fa mixtures. A multi-fluid approximation based on pure-fluid Helmholtz energy equations of state forms the basis of the property model. The Helmholtz energy of the mixture is expressed as the sum of the ideal gas contribution, the compressibility contribution (real fluid contribution), and the contribution from mixing to represent the deviation from ideal mixtures. The independent variables are the temperature, molar volume, and composition. The model can be used to calculate all thermodynamic properties of the mixtures at various compositions. The estimated uncertainties in calculated properties from the model are ±0.2 % for the bubble and dew point pressures and ±0.24 % for the liquid and vapor densities. The critical parameters of the mixtures are properly represented with the model. The calculated critical temperatures correspond to experimental values within ±0.5 K.