Refractive index and volume reduction of PAG oil/R290 mixture

The mixing behavior of refrigerants with compressor lubricants influences system efficiency, lubrication performance, and operational reliability. In this study, the solubility and mixture behavior of propane (R290) in polyalkylene glycol (PAG) oil were investigated experimentally at 30–50 °C. Complete miscibility was confirmed over the investigated range, with no phase separation observed. Refractive index measurements were used to characterize mixture composition and establish correlations in both mass- and volume-fraction forms. Post-mixing volume measurements revealed a measurable reduction and indicated negative excess volume with a bell-shaped dependence on composition described by a Gaussian function. Experimental mixture densities exceeded predictions from ideal linear mixing and Gladstone–Dale models. To address this discrepancy, a new density formulation based on volume reduction coefficient was proposed, indicating close agreement with densities calculated from measured mass and contracted volume. These results provide an improved framework for density estimation and mixture characterization in R290–lubricant systems relevant to refrigerant compressors.