Viscosity and Density of a Polyol Ester Lubricating Oil Saturated with Compressed Hydrofluoroolefin Refrigerants

Hydrofluoroolefins (HFOs) are currently being developed to replace hydrofluorocarbons (HFCs) with high global warming potential (GWP) in air-conditioning and refrigeration systems. The development of low-GWP HFOs requires detailed knowledge of the key thermophysical properties of these refrigerants with commonly used lubricating oils at varying operational conditions. The liquid-phase dynamic viscosity and density data for a synthetic polyol ester lubricating oil (ISO VG 32) saturated with compressed 2,3,3,3-tetrafluoropropene (R-1234yf) and trans-1,3,3,3-tetrafluoropropene (R-1234ze(E)) were measured over temperatures ranging from 248.15 to 348.15 K and pressures up to 0.6 MPa. The liquid compositions for the viscosity and density data were calculated using previously measured vapor-liquid equilibrium data and models. The liquid phase viscosity decreased significantly with increased composition of the refrigerant. The experimental viscosity and density obtained for each refrigerant and lubricating oil system were successfully correlated using Redlich-Kister expansions for excess volume and excess viscosity. From the data and modeling, the kinematic viscosities were calculated and Daniel plots were generated. In addition, the previously measured diffusivities for each HFO/ISO VG 32 lubricating oil system were well correlated with the reported experimental viscosity data according to the StokesEinstein theory.