Phase equilibrium and diffusivities of hydrofluorocarbons in a synthetic polyol ester lubricant

Detailed knowledge about the thermophysical properties of refrigerant/lubricant systems, such as solubility and diffusivity, are required for the design, operation, and long-term reliability of heating, ventilation, air-conditioning, and refrigeration equipment. Herein, vapor–liquid equilibrium of hydrofluorocarbons (HFCs) 1,1,1,2-tetrafluoroethane (R-134a), pentafluoroethane (R-125), and difluoromethane (R-32) in a polyol ester oil (ISO VG 32) were measured using a gravimetric microbalance at temperatures ranging from 248.15 to 348.15 K and up to 1.0 MPa of pressure. The experimental solubility data of each refrigerant/lubricant system were successfully modeled using the nonrandom two liquid activity coefficient model. A one-dimensional diffusion equation was applied on time-dependent absorption data to determine binary diffusion coefficients (D) for the refrigerants in the ISO VG 32 lubricant. Finally, Stokes–Einstein diffusing radius calculations support the hypothesis that HFCs dissolve into ISO VG 32 lubricant as individual molecules rather than associated complexes.