A new formulation is presented for the thermodynamic. properties of refrigerant 143a (1,1,1-trifluoroethane, CH3-CF3) based upon available experimental data. The formulation can be used for the calculation of density, heat capacity, speed of sound, energy, and saturation properties using an equation of state explicit in Helmholtz energy. Ancillary equations are given for the ideal gas heat capacity, the vapor pressure, and for the saturated liquid and vapor densities as functions of temperature. Comparisons to available experimental data are given that establish the accuracy of calculated properties using this equation of state. The estimated uncertainties of properties calculated using the new equation are 0.1% in density, 0.5% in heat capacities, 0.02% in the speed of sound for the vapor at pressures less than 1 MPa, 0.5% in the speed of sound elsewhere, and 0.1% in vapor pressure, except in the critical region. The equation is valid for temperatures from the triple point temperature (161.34 K) to 450 K and pressures up to 50 MPa, and can be extrapolated to 650 K. It has been accepted as an international standard formulation for the properties of R-143a by the International Energy Agency-Annex 18. (C) 2001 by the U.S Secretary of Commerce on behalf of the United States. All rights reserved.
