An international standard formulation for the thermodynamic properties of 1,1,1-trifluoroethane (HFC-143a) for temperatures from 161 to 450 K and pressures to 50 MPa

A new formulation is presented for the thermodynamic. properties of refrige rant 143a (1,1,1-trifluoroethane, CH3-CF3) based upon available experimenta l data. The formulation can be used for the calculation of density, heat ca pacity, speed of sound, energy, and saturation properties using an equation of state explicit in Helmholtz energy. Ancillary equations are given for t he ideal gas heat capacity, the vapor pressure, and for the saturated liqui d and vapor densities as functions of temperature. Comparisons to available experimental data are given that establish the accuracy of calculated prop erties using this equation of state. The estimated uncertainties of propert ies calculated using the new equation are 0.1% in density, 0.5% in heat cap acities, 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, exc ept 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, a nd can be extrapolated to 650 K. It has been accepted as an international s tandard formulation for the properties of R-143a by the International Energ y Agency-Annex 18. (C) 2001 by the U.S Secretary of Commerce on behalf of t he United States. All rights reserved.