STATIC RELATIVE PERMITTIVITY OF CARBON-DIOXIDE AND NITROUS-OXIDE UP TO 30-MPA

The static relative permittivity epsilon(r) of carbon dioxide and nitrous oxide has been measured in a temperature range from 273.15 to 353.15 K at pressures up to 30 MPa. The measurements were performed by means of a transformer ratio-arm bridge with a three-terminal capacitance cell installed in a pressure vessel at frequencies between 10 to 50 kHz. The newly-designed capacitance cell and pressure apparatus are described. Experimental epsilon(r)-values obtained for the two fluids were estimated to be accurate to within +/-0.02%. The critical relative permittivity epsilon(r,C), evaluated from the epsilon(r)-values of coexisting saturated vapor and saturated liquid, was 1.267+/-0.001 for carbon dioxide and 1.288+/-0.003 for nitrous oxide. The density dependence of the epsilon(r)-values can be expressed by a quadratic function of density, independent of temperature. The epsilon(r)-data for each fluid were combined with available densities from the literature to calculate the molar polarization P(m) given by the Clausius-Mossotti (CM) equation. Some consideration is given for the coefficients of the dielectric virial equation, i.e., the expansion of the CM equation in powers of density.