Miscibility and solubility of R290 and R1270 in POE, PVE, and PAG lubricants: Implications for refrigerant retention and charge optimization

In refrigeration, air conditioning, and heat pump systems, the selection of refrigerant and lubricant oil is crucial for system performance, energy efficiency, compressor reliability, and operational safety, especially for flammable low-GWP refrigerants. Refrigerant dissolution in lubricant oil significantly affects system charge distribution, compressor lubrication reliability, and leakage safety. To clarify the interaction characteristics between refrigerants and lubricants and provide practical guidance for lubricant selection and system charge optimization, the miscibility, solubility, Henry constant, normalized fugacity, and refrigerant retention behavior of R290 and R1270 with POE68, PVE68, and PAG68 were systematically investigated using the visual cooling method and the isochoric saturation method. The results showed that all refrigerant-lubricant systems exhibited good miscibility, and the solubility of both refrigerants increased with increasing pressure and decreased with increasing temperature. POE68 showed the strongest dissolution ability for R290, while PAG68 exhibited the lowest solubility for R1270. All systems exhibited negative deviation from Raoult’s law, indicating strong attractive interactions between refrigerant molecules and lubricant molecules. When the total refrigerant charge was 700 g, the retained refrigerant mass in lubricant oil increased from 5.8 g to 208.4 g with increasing mole fraction, which could reduce the effective circulating refrigerant charge and increase the risks of oil foaming and delayed refrigerant release. Among the three lubricants, PVE68 provided a better balance between refrigerant dissolution, oil return performance, system charge stability, and compressor safety, showing good application potential in refrigeration and heat pump systems.