Relative permittivity of mixtures of R-134a and R-1234yf and a polyol ester lubricating oil

Abstract

The relative permittivity (dielectric constant) of mixtures of a polyol ester (POE) ISO VG 10 lubricating oil and refrigerants R-134a and R-1234yf was evaluated experimentally for temperatures ranging from 298 to 328 K. The experimental apparatus was designed and built specifically for determining the dielectric properties of mixtures of lubricants and liquified gases (refrigerants) at high pressures. The mixture relative permittivity was inversely proportional to the temperature and directly proportional to the refrigerant concentration. The relative permittivity of the R-1234yf mixture was slightly lower than that of the R-134a mixture at identical conditions. The Böttcher mixing rule for the relative permittivity and the Oster rule for the mixture polarity showed the best agreement with the experimental data, with root-mean square (RMS) deviations smaller than 1%.