Thermodynamically Consistent Determination of Virial Coefficients from Speed-of-Sound Measurements

As an Example for Gaseous R-134a

Abstract

This paper proposes a procedure on the thermodynamically consistent determination of virial coefficients from speed-of-sound measurements. Using the speed-of-sound values for gaseous l, 1, 1, 2-tetrafluoroethane (R-134a) which have already been reported in the previous paper, the 2nd and 3rd virial coefficients of R-134a were determined by means of thermodynamic relation among the virial coefficients of two different virial equations of state with respect to pressure and density. The present virial equation of state regarding density expansion can represent not only the speed-of-sound values but also the PρT-data for R-134a with the smallest standard deviation ever reported. The standard deviation of the speed-of-sound data from the virial equation of state is ±49 ppm. And the standard deviation of the PρT-measurements by Zhang et al. (1996) and by Tillner-Roth and Baehr (1992) from the virial equation of state against density is ±0.04%. The comparison of the virial equation of state with available other equations of state clearly shows the reduced uncertainty of the present equation of state.