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

Abstract

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.

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

“… a Molar mass of the refrigerants was obtained from the National Institute of Standards and Technology (NIST) REFPROP v.10.0 database b Purities were provided by the supplier. c Molar mass of the ISO VG 32 lubricating oil was determined by Nuclear Magnetic Resonance spectroscopy and previously reported by our group …”

“…The full name, CAS number, molar mass, and respective supplier of the refrigerants and ISO VG 32 lubricating oil are reported in Table . The ISO VG 32 lubricating oil is mainly composed of pentaerythritol esters, such as n -heptanoate (45.5 mol %), n -pentanoate (32.7 mol %), 3,5,5-trimethylhexanoate (16.3 mol %), and 3-methylbutanoate (5.5 mol %), as determined by various NMR techniques; see ref .…”

“…Molar mass of the ISO VG 32 lubricating oil was determined by Nuclear Magnetic Resonance spectroscopy and previously reported by our group …”

“…For the ISO VG 32 lubricating oil, previously published pure component density and dynamic viscosity data were correlated with simple temperature-dependent expressions. The pure lubricating oil density was correlated with a Rackett-type expression: where V̂ 2 is the specific volume of the lubricating oil, T is the temperature in K, and d j are adjustable parameters, where j ∈ {1,2,3,4}.…”

“…The present study provides highly accurate data on dynamic viscosity and liquid density for HFOs (R-1234yf and R-1234ze­(E)) in a common synthetic POE lubricating oil (ISO VG 32) over a temperature range from 248.15 to 348.15 K and pressures up to 0.6 MPa. A POE ISO VG 32 lubricating oil was selected based on its high compatibility with many refrigerants and blends and because it is a widely used POE oil for HFC and HFO compressor systems . A previous study on the vapor–liquid equilibrium ( PTx ) for R-1234yf and R-1234ze­(E) in ISO VG 32 lubricating oil has been published, where the liquid-phase HFO compositions were measured at the same temperature and pressures considered in this study .…”