Measurement of Lubricating Oil Flow Rate in a Circular Pipe Simulating a Discharge Pipe of an Air-Conditioning Compressor

A non-contact measurement technique for the volumetric flow rate of oil droplets in compressor discharge pipes is proposed to improve the quantitative evaluation of oil carryover in air-conditioning compressors. Oil carryover reduces lubrication performance and may cause mechanical failure; therefore, accurate measurement of oil circulation is essential. The proposed method utilizes scattered light intensity from oil droplets illuminated by a laser sheet. The droplet size distribution is assumed with the Nukiyama-Tanasawa distribution, and volumetric flow rate of droplets is estimated by the size distribution derived from the light intensity scattered from droplets passing through the cross-section of the pipe. To validate the proposed technique, the volumetric flow rate of oil droplets was measured in a transparent acrylic circular pipe used as a substitute for the discharge pipe of an actual compressor. Oil droplets were generated by pressure atomization and introduced into the pipe by airflow under various velocity conditions ranging from 6 to 21 m/s. The volumetric flow rate of the droplets rate was measured by collecting the droplets using a mist trap to compare it with that estimated by the proposed technique, and droplet size distributions were obtained using a shadowgraph technique to determine parameters of the Nukiyama-Tanasawa distribution. The proposed technique was applied to the volumetric flow rate of the droplets, and a clear correlation between scattered light intensity and oil droplet volumetric flow rate was confirmed. The estimated values agreed with those obtained by a mist trap method within a range of +40% overestimation and -20% underestimation. Overall, the proposed technique demonstrates feasibility as a non-contact technique for measuring oil droplet flow rate and has potential for application to actual compressor systems.