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This paper reports viscosity data for mixtures containing a refrigerant(HFC-134a) and a lubricant (triethylene glycol dimethyether, TriEGDME, ortetraethylene glycol dimethyl ether, TEGDME), at 12% of TriEGDME or 14% massfraction of TEGDME. The measurements (140 data points) were obtained at variouspressures (between 10 and 140 MPa) in the monophasic liquid state from 293.15to 373.15 K. Because HFC-134a and the polyethers are not in the same singlephase at normal pressure and temperature (the refrigerant is a gas, whereas thepolyethers are liquids), accurate measurements of their mixtures requirespecific procedures for preparation of the samples and filling of theapparatus. A specially designed isobaric-transfer falling-body viscometer isused in this work. The viscosities of the mixtures are, on average, 40% higherthan that of the pure refrigerant, and this increase is more noticeable at lowtemperatures. The experimental viscosities have been used to check thepredictive and correlation ability of several viscosity models (mixing rules,Geller and Davis method, self-referencing model, hard-sphere theory,free-volume model, and friction theory). Most of the studied modelsunderestimate the dynamic viscosity values over all of the temperature andpressure ranges investigated.

Dynamic Viscosity for HFC-134a + Polyether Mixtures up to 373.15 K and 140 MPa at Low Polyether Concentration. Measurements and Modeling