Experimental studies of thermodynamic properties of R744-oil-mixtures up to 140 °C and 150 bar

•Measurement of miscibility, density, vapour pressure, and viscosity.•Based on DIN and ASTM with self-built and commercial equipment.•Accuracy meets the requirements of industrial and commercial refrigeration.•Discussion of miscibility and solubility in supercritical region of the mixture.•Discussion on topics regarding viscosity reduction by diluted refrigerant.

The knowledge of the thermodynamic properties of pure refrigerants and refrigeration oils is a precondition for developing a refrigeration cycle. In addition, the miscibility of the refrigerant in the oil and the influence of the working fluids on the properties of the mixtures are to be known. For the refrigerant carbon dioxide, several types of refrigeration oils with different miscibility/solubility and viscosity properties can be used. In MAC applications for passenger cars, PAG oils are preferred.In this paper, new methods and equipment to measure the thermodynamic properties miscibility, density, vapour pressure, solubility, and viscosity are discussed and examples of experimental data are shown for a R744-oil-mixture. At first the miscibility gap was examined by visual observation of the mixtures. Then the other properties were measured in the miscible range from 70 to 100% oil up to 140 °C and up to 150 bar.