The market of air conditioners has been booming since the invention of the first modern electrical air conditioning (AC) system in 1902 and is estimated to reach 110.97 million units in 2018. Rotary compressor is widely used is small AC appliances. It uses one or multiple high-speed rotating eccentric rolling piston to compress refrigerant vapor in the cylinder. Low-pressure, low-temperature refrigerant vapor from the evaporator is vented into the space between the rolling piston and the cylinder through the suction port and compressed as the eccentric piston revolves and then discharged at the other side of the cylinder through the discharge port. The lubricant oil is used in the rotary compressor to lubricate and seal the clearance of sliding parts, e.g., between the rolling piston and the cylinder and between the vane and the cylinder. However, part of oil in the cylinder is discharged together with the compressed refrigerant vapor through the discharge port, and experiences a set of complicated, highly-coupled atomization process during the discharge process. The formed oil droplets then enter the lower cavity of the rotary compressor. The portion of the oil ultimately exhausted from the rotary compressor can be characterized by the ratio of discharged oil volume to the total oil volume or so-called Oil Discharge Ratio (ODR). High ODR will lower the oil level in the compressor and, as a result, reduce the reliability of the compressor. Also, too much oil in the pipe of the system deteriorates the heat transfer of the condenser and the evaporator, resulting in the decreased system efficiency. Thus, studying the atomization process from the discharge port and the oil droplet behavior in the lower cavity of a rotary compressor can help to control the ODR, which is a key issue for the design of the rotary compressor. In this study, a compressor test rig is built to run the modified rotary compressor that has several observation optical windows around the lower cavity. The oil droplet size distribution in the lower cavity has been obtained at shaft’s rotating frequency of 30 Hz by shadowgraphy . The discharge process of oil from the discharge port is visualized at 30 Hz with time-resolved images, and the velocity field of oil droplets is retrieved by Optical Flow Velocimetry. It is found that denser oil droplets with larger *D*~10~ and *D*~32~ are observed in the lower cavity at 30 Hz, comparing to the oil droplets observed in the upper cavity. Also, the time-resolved images show that the discharge process of oil from the discharge port can be divided into five phases with more oil droplets been discharged in the first two phases. Moreover, higher velocity is observed at the edge of the groove than in the core of the jet because of the existence of the valve. Secondary breakup of vibrational type and the breakup of ligaments are also observed, which produce smaller droplets.


Characterization of Oil Droplets in the Lower Cavity of a Rotary Compressor

Division / Sponsors: 
Heat Transfer Division (HTD), Fluids Engineering Division (FED)

Heat Transfer Summer Conference
Paper Proceedings: https://asmedigitalcollection.asme.org/HT/HT2020/volume/83709

18th International Conference on Nanochannels, Microchannels, and Minichannels
Paper Proceedings: https://asmedigitalcollection.asme.org/ICNMM/ICNMM2020/volume/83693

Fluids Engineering Division Summer Meeting
Paper Proceedings: https://asmedigitalcollection.asme.org/FEDSM/FEDSM2020/volume/83716

HT-ICNMM2020 - Virtual Conference, SHTC - Virtual Conference, FEDSM2020 - Virtual Conference

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