Experimental data on the viscosity of mixtures of CO2 and lubricant oil were acquired and correlated using an excess-property approach based on the classical Eyring liquid viscosity model. Three oils of different types and viscosity grades (alkylbenzene AB ISO 32, mineral MO ISO 50 and polyol ester POE ISO 68) were evaluated at temperatures ranging from 36.5 to 82ºC. The excess activation energy for viscous flow was successfully correlated as a function of temperature and concentration using Redlich-Kister polynomial expansions with up to three terms. Large departures from the ideal solution viscosity behavior have been identified in all mixtures. The nature of the observed deviations has been explored in the light of their dependence on temperature, refrigerant concentration and oil type. The Katti and Chaudry (1964) model of the activation energy of viscous flow displayed the best correlation of the experimental data, with RMS deviations of 4.6% (AB ISO 32), 3.3% (MO ISO 50) and 2.8% (POE ISO 68).
CO2-lubricant oil mixture; viscosity; experimental data; modeling
