A thermodynamic equation of state for pentafluoroethane (R-125)

We developed a fundamental equation of state for pentafluoroethane (R-125, CHF2CF3) which is represented in terms of a non-dimensional Helmholtz free energy. The equation has been established on the basis of selected measurem ents of the pressure-density-temperature relation, speed of sound, heat cap acities, and saturation properties. Linear and non-linear regression analys is was employed to determine the functional form and the numerical paramete rs. The equation represents all the thermodynamic properties of R-125 in th e liquid and gaseous phases for temperatures between the triple point and 4 70 K, and pressures up to 35 MPa. The uncertainties are estimated to be abo ut +/- 0.05 % or 0.1 kPa for the vapor pressure, +/- 0.05 % for the liquid and vapor densities, about +/- 1 % for the isobaric and isochoric heat capa cities in the liquid, and +/- 0.5 % or +/- 0.02 % for the speed of sound in the liquid and vapor, respectively.