Lubricity of selected oils in mixtures with the refrigerants R452A, R404A, and R600a

The essential problem in the operation of refrigeration compressors is the change in lubricity of oils in the mixture with a refrigerant. The validity of the issue is intensified by the tendency to replace refrigerants with more ecological ones. For the new refrigerants, one should select the right compressor oil. The paper describes a method of assessment of lubricity on the basis of the wear of the model block-on-ring tribocontact following the operation in the oil-refrigerant mixture. The method was used for a comparative assessment of various oils in the mixture with the refrigerant R404A and its successor - R452A. In addition, three mineral oils (MO) with the natural refrigerant R600a were examined. In all of the examined instances, significant differences in lubricity in the group of compared oils (replacements) were found. The obtained results confirm the suitability of the method for assessing lubricity of a wide group of substances: POE/R404A, POE/R452A, MO/R600a. One also confirmed the suitability of the method for initial selection of oil for new refrigerants. The method can be applied for different mechanisms of oil-refrigerant mixture formation: intermolecular diffusion for R600a, intermolecular diffusion and natural convection for R452A. Furthermore, the impact of lowering the temperature (pressure) on lubricity of the oil-refrigerant mixture was examined. In the analyzed case, however, the observed differences were not significant.