Lubricant, oil, holdup, alternative refrigerants, air-conditioning
Lubricants are utilized in air-conditioning systems for the purpose of decreasing friction and wear within the compressor. While ideally the lubricant remains in the compressor, some lubricant is entrained and transported by the refrigerant to the other system components. During operational transients, the lubricant is redistributed throughout the various system components. The equilibrium distribution of lubricant depends among other things on fluid properties, phase change processes, flow rates, geometries, and operating conditions. Experiments were conducted in a commercially available, split-system, residential, air-conditioning system with a nominal 3-ton capacity that could be operated both as an air-conditioner and a heat-pump. While the system was designed to operate with R410A, most of the testing was conducted with pure R32, which is a leading candidate for R410A replacement pending regulatory discontinuation of its other constituent: R125. The lubricants used in this study were traditional and advanced polyol ester lubricants. Advanced polyol ester lubricants promise to improve lubricity and wear protection compared to current lubricants. The lubricants had nominal viscosities ranging from 32 to 80 cSt. To inventory the distribution of refrigerant and lubricant, the system was modified by the installation of ball valves which could be utilized to separate the system into its constituents: compressor, condenser, liquid line, evaporator, suction line, and accumulator. The system was brought to equilibrium at conditions A, B, C, H1, and H2 which are defined in AHRI Standard 210/240. After maintaining equilibrium, simultaneously the compressor being shut off and the ball valves were closed which isolated refrigerant and lubricant within each component. The components were subsequently removed and weighed in a manner which allowed the mass of refrigerant and lubricant in each component to be determined. Analysis of the results focuses on the change in mass distribution due to refrigerant-lubricant mixture properties and due to changes in operating conditions. The implications of the net migration of lubricant from the compressor to the remainder of the system will also be discussed.