Vapor-liquid equilibria of a low GWP refrigerant, R-1234ze(E), mixed with a POE lubricant

Abstract

Novel vapor-liquid-equilibria data (P-T-x) and liquid densities of binary mixtures of an emerging low-GWP (Global Warming Potential) refrigerant, R-1234ze(E), and a polyol ester (POE) oil, RL68H, are measured. Data are presented for oil mass fractions ranging from 0 to 0.85 over a temperature range from -10 to 60°C, and the results are compared to the properties of mixtures of R-134a with RL68H. In addition to providing new pure-refrigerant and refrigerant/oil property data, a comparison of the performance of five mixture models is undertaken, namely: the Wilson model, NRTL, UNIQUAC, Heil, and Raoult’s law. Overall, the Heil model provides the best agreement in pressure predictions for R-1234ze(E)/RL68H mixtures, with RMS deviations less than 0.5%, while NRTL RMS deviations are less than 1%. However, comparable performance was found for the much simpler Raoult’s law, with increased deviations at the highest oil concentration. Model sensitivity and applicability of Raoult’s law for refrigerant/oil mixtures in general are investigated. The experimental data and modeling results presented are especially valuable for engineers working in the automotive air-conditioning and refrigeration industries. The refrigerant R-1234ze(E) is one of the leading alternatives for replacing R-134a and is a member of the HFO family of chemicals that includes other low-GWP refrigerants. Accurate models for the new refrigerants and refrigerant/oil mixtures are essential for designing and analyzing refrigeration and air-conditioning systems with reduced environmental impact.