Lubrication Analysis of Rotary Compressors for HFC Refrigerants

In this study, a practical numerical analysis has been developed in order to investigate the lubrication characteristics between a rolling piston and a crank of rotary compressors. This analysis is treated as a coupled problem of the momentum equations and the Reynolds equation of oil film. Using this analysis, the lubrication characteristics between the rolling piston and the crank for 2-cylinder rotary compressors were evaluated for R22 and R410A. Furthermore, the lubrication characteristics on the journal bearings were also analyzed using the already developed tool [ 1]. Measured pressure and oil viscosity in a inverter driven heat pump system were used as the analysis conditions. The oil film thickness and the motions of the rolling piston and the motor rotor were obtained as the analysis results. It made clear that the lubrication characteristics of the rolling piston and the journal bearings with R41 OA refrigerant is better than those with R22. INTRODUCTION R410A (R32/125, 50/50wt%) is an alternative refrigerant ofR22 for air-conditioners, and its capacities have been evaluated widely. Mineral oil is applicable to R22 system as lubricant, but it cannot be used in R410A system because of poor miscibility with R410A. Therefore, polyolester oil which is miscible with R41 OA is mainly used as alternative oil. The cooling capacity of R41 OA derived from the refrigerant property is about 1.4 times as much as that of R22[2]. So, the discharge volume of compressors for R41 OA is required to redesign to adjust the cooling capacity. It is important to investigate lubrication characteristics of compressors with R410A in order to develop the optimum lubricant and to design compressors for R410A. Therefore, many durability tests and numerical analysis were carried out to evaluate the lubrication characteristics with R 41 OA. In the present study, we developed the practical program for lubrication analysis between the rolling piston and the crank of rotary compressors. The selection of lubricating oil and the optimum design of rotary compressors were done by using this analysis and another analysis for journal bearings in addition to the experimental results of the compressor durability tests and oil lubricity evaluations [3]. In this paper, at first, the governing equations and the procedure of the analysis are described. As an example of the analysis results, the optimum lubrication characteristics between the rolling piston and the crank and on the journal bearings of the 2-cylinder rotary compressor for R 41 OA are shown by relatively comparing with the analysis results for R22. GOVERNING EQUATIONS Fig.l shows the schematic drawing of the compression part in a rotary compressor, and Fig.2 shows the schematic drawing of rolling-piston/crank and its coordinate system for the analysis. The rolling piston is loaded large dynamic forces such as unbalanced forces, gas forces and vane forces. Therefore, the Reynolds equations are used to calculate the reaction force of oil film.