Lubrication quality of compressor rolling bearings with oil-refrigerant mixtures

Abstract

In refrigerant compressor, rolling bearings are lubricated with a mixture of oil and refrigerant. This has always represented a challenge for the bearing lubrication quality estimation (e.g. kappa or lambda parameters). Even if the dilution rate of the refrigerant is known, the exact effect on the lubricant film thickness remains doubtful due to the unknown piezo-viscosity and compressibility of the refrigerant and their variation with pressure and temperature. In the current paper, existing mixing laws for viscosity and piezo-viscosity are examined and adapted to better represent actual measurements. The results are compared with published Daniel plots showing reasonable agreement. Once this is done a modification to the bearing lubrication quality parameter kappa is proposed to better reflect the effect of the refrigerant on the lubrication quality of compressor rolling bearings. This is a first step in the direction of predicting the bearing life for this challenging application.