A bench evaluation test for refrigeration oils in a refrigeration system using a screw compressor

Refrigeration oil has a large effect on the performance of refrigeration systems. However, the physical and chemical indexes of fresh refrigeration oils often fail to reflect the actual operating characteristics, especially with respect to the degradation of refrigeration oils. In this paper, a bench evaluation test of refrigeration oils was carried out to investigate the degradation of synthetic refrigeration oils used with the refrigerant R134a, in a purpose-built, full-scale refrigeration system utilizing a screw compressor. To accelerate the degradation process of the refrigeration oil, the discharge temperature at the exit of the compressor was turned to a high level. Comparison tests of a mature refrigeration oil type A and a newly developed oil type B were performed under the same working conditions with 500 h of operating time. The performance of the screw compressor and refrigeration system was analyzed. The abrasion of the screw rotors and carbon deposition at the discharge port was investigated. Results showed that the bench evaluation test successfully predicted the degradation process of the refrigeration oils. The evolution analysis of the refrigeration oil viscosity and acid value during the bench evaluation test indicated that 15% of the physical and chemical indexes for refrigeration oil drain were too strict. Research work in this paper showed a more practical method to evaluate the performance of refrigeration oils through the bench evaluation test.