Experimental study of the lubricant-refrigerant flow in a rotary compressor

Abstract

Lubricant oil is used in the rotary compressor to lubricate the bearings and to seal the clearance of sliding parts. However, a portion of lubricant oil in the upper cavity will ultimately exhaust from the compressor through the discharge tube, carried by the refrigerant. The accumulated lubricant in the tubes will deteriorate the heat transfer of the condenser and the evaporator, resulting in decreased efficiency. This work focuses on characterizing the pathway of lubricant droplets in a rotary compressor. In-situ measurements include lubricant spray penetration velocity at different phases in a rotating cycle and droplet velocities at different locations, i.e., lower cavity, above the rotor/stator, and at the discharge tube level, different frequencies, and different pressures via time-resolved shadowgraph. Particle Image Velocimetry (PIV) and Optical Flow Velocimetry (OFV) are adopted to quantify the velocities of spray and droplets. The penetration velocity of the lubricant spray in the lower cavity, horizontal swirling velocity above the rotor/stator and at the discharge tube level, and the vertical recirculation velocity above the rotor/stator are characterized. The results support a droplet pathway model in the rotary compressor that can guide the optimization of the next-generation rotary compressors.