Ultra High Pressure Tribometer for Testing CO2 Refrigerant at Chamber Pressures up to 2000 psi to Simulate Compressor Conditions

Abstract

The growing interest for using the natural refrigerant carbon dioxide (CO2) in refrigeration and air-conditioning applications instead of HFC refrigerants, due to environmental concerns, has led to the development of an ultra high pressure tribometer (UHPT) specifically tailored for testing in CO2 environment. The existing research on tribology related to CO2 environment has focused on investigations at relatively low chamber pressures due to equipment restrictions. The UHPT is a unique tribometer that has been custom designed and manufactured to allow testing under CO2 refrigerant at environmental pressures comparable to those found in compressors. A special housing, which surrounds the tribological surfaces subject to testing, is capable of withstanding chamber pressures up to 13.8 MPa (2000 psi) and can be temperature controlled from 0°C to 100°C via a thermal control system. A multi-axis strain gauge force transducer measures the applied load, frictional forces, and moments during friction testing, and computer control permits different loading profiles. Using this machine, experiments were performed at a range of pressures between 1.4 MPa (200 psi) and 6.9 MPa (1000 psi) of CO2 refrigerant. The results suggest a slightly better tribological performance at higher pressures compared to lower pressures.