The first calculations of film thickness for an oil/refrigerant system using quantitative elastohydrodynamics are reported in this work. It is demonstrated that primary measurements of the properties of the oil/refrigerant system can be employed to accurately predict film thickness in concentrated contacts. An unusual response to lubricant inlet temperature is revealed, wherein the film thickness may increase with temperature as a result of decreasing refrigerant solubility in oil when the inlet pressure is high. There is competition between the reduction in viscosity of the oil and the reduction of refrigerant concentration with increased temperature. For high inlet pressure, the dilution effect is dominant, whereas for low inlet pressure, the temperature dependence of the viscosity of the solution dominates over the range of inlet temperatures considered. It seems that only central film thicknesses have been experimentally measured for oil/refrigerant systems leaving these calculations as the only means of assessing the minimum.

A fixture was fabricated for the purpose of restraining the expansion of an existing metal bellows piezometer so that a refrigerant and oil mixture can be admitted under pressure. Measurements on a polyol ester (POE) with 9.2 wt.% of R134a show that the addition of refrigerant slightly increases compressibility. The previously reported reduction in compressibility (increase in bulk modulus) by Tuomas and Isaksson (2006, “Compressibility of Oil/Refrigerant Lubricants in Elasto-Hydrodynamic Contacts,” ASME J. Tribol., 128(1), pp. 218–220) of an ISO 68 POE when mixed with R134a cannot be supported by precise measurements of the volume compression. The increased compressibility found by Comuñas and co-workers (2002, “High-Pressure Volumetric Behavior of x 1, 1, 1, 2-Tetrafluoroethane + (1 − x) 2, 5, 8, 11, 14-Pentaoxapentadecane (TEGDME) Mixtures,” J. Chem. Eng. Data, 47(2), pp. 233–238) is the correct trend. The Tait equation of state (EoS) has been fitted to the data for both the neat POE and its 9.2% by weight mixture with refrigerant. The usual problem was encountered for the mixture with the Tait EoS at low pressure where the compressibility becomes greater than predicted due to proximity to the vapor dome. The measured relative volumes of the mixture can be used to collapse the viscosity to a master curve when plotted against the Ashurst–Hoover thermodynamic scaling parameter. The thermodynamic scaling interaction parameter is approximately the same as for the neat oil.

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Application of the new quantitative elastohydrodynamics to the concentrated contacts operating within refrigerant compressors will require the accurate description of the viscosity of the lubricant that is diluted by the refrigerant. This article presents extensive viscosity measurements on polyolester and polyvinylether oils and their mixtures with low mass fractions (2–23%) of refrigerants R134a and R410a. Pressures up to 400 MPa and temperatures to 100°C were reached. Correlations are presented to predict the viscosity and pressure–viscosity coefficients at arbitrary temperatures and pressures and concentrations. Pressure–viscosity coefficients are compared with those derived from film thickness measurements using one of the popular definitions for the coefficient. Where comparisons can be made, the film‐derived pressure–viscosity coefficients were mostly inaccurate. Part of the problem has been the lack of a single well‐accepted and rigorous definition of the pressure–viscosity coefficient and the lack of an accurate film thickness formula that employs that definition. Copyright © 2017 John Wiley & Sons, Ltd.