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

Abstract

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 Stokes–Einstein theory.

Viscosity and Density of an ISO VG 32 Polyol Ester Lubricant Saturated with Compressed Hydrofluorocarbon Gases: R-134a, R-32, and R-125

“…Similar qualitative trends were obtained for the systems R-1234yf/ISO VG 32 and R-1234ze (E)/ISO VG 32 with refrigerant composition . Similar findings were reported by Cavestri about the effect of R-134a composition on the liquid density of EMKARATE RL32S lubricating oil at various temperatures .…”

“…The dynamic viscosity, liquid density, and kinematic viscosity data for the pure ISO VG 32 lubricating oil over temperatures ranging from 248.15 to 348.15 K at ambient pressure were previously reported by our group , and are showed in Table .…”

“…In general, the Redlich–Kister model is in good agreement with those found in the literature. For instance, Morais et al correlated the experimental viscosity data for R-1234yf/ISO VG 32 and R-1234ze (E)/ISO VG 32 binary systems using the Redlich–Kister model and reported an AARD of 7.8 and 6.5%, respectively . Also, Neto and Barbosa correlated the dynamic viscosity of R-600a (isobutane) in POE ISO VG 7 lubricant using the general PC-SAFT f-theory , resulting in an AAD of 5.3%…”

“…Correlations for the solubility, viscosity, and density for the HFC/ISO VG 32 lubricating oil systems were previously described in detail. , A brief overview will be given here. The solubility of the HFCs in the lubricating oil at each temperature and pressure was predicted from an nonrandom two-liquid (NRTL) activity coefficient model fit to vapor–liquid equilibrium data that we measured in a previous study at the same isotherms and similar pressure ranges .…”

“…Hessell and Urrego measured the viscosity of several HFC and HFO blends (ternary, quaternary, and quinary) in three undisclosed POE ISO 32 lubricants over a range of temperatures and at pressures that are typical for the compressor suction and discharge . We have recently reported the density and viscosity of two HFOs ( trans -1,3,3,3-tetrafluoropropene (R-1234ze) and 2,3,3,3-Tetrafluoropropene (R-1234yf)) in a POE lubricant at temperatures between 248.15 to 348.15 K and pressures up to 0.6 MPa …”