Characteristics of oil annular-mist flow in the compressor discharge pipe

Oil is essential to the compressor, but oil brings side effects on the heat exchanger performance. It is preferred to reduce the amount of oil circulating in the system and retain the oil in the compressor for both reliability and efficiency reasons. Oil leaves the compression chamber in the form of mist. Oil droplets are propelled by refrigerant vapor flow and form a developing annular-mist flow in the discharge pipe, as droplets gradually attach to the inner wall. In this paper, a video-based method to quantify the oil flow in the compressor discharge pipe is presented. Oil droplet size, oil droplet velocity, oil film thickness, and oil film wave velocity are measured at different mass flow rates and compressor speed. The measurements show a variety of oil flow parameters as functions of distance along the discharge pipe. The impact of system flow rate, compressor type, and oil properties are also discussed. The characteristics of oil discharged by the compressor provide essential information for oil separator design and optimization. The research approach also has the potential to be applied in other multiphase studies.