3179 (RP-356) -- Measuring the Concentration of a Flowing Oil-Refrigerant Mixture with a Vibrating U-Tube Densimeter ✓ Most Recent

A commercially available vibrating U-tube densimeter has been evaluated as a sensor for measuring the concentration of oil in the liquid line of a refrigeration system. Calibration and performance tests were conducted under simulated liquid-line conditions for R-12/naphthenic oil, R-22/naphthenic oil, and R-502/alkylbenzene oil mixtures in concentrations of 0 to 30 weight-percent. Test temperatures ranged from 70 to 115 F (21.1 to 46.1°C) at pressures corresponding to approximately 6 F (3.3°C) subcooling through the densimeter. Statistical analysis of the data showed that the densimeter can be used to measure the flowing oil concentration in R-12/naphthenic oil mixtures with an uncertainty of ±1 weight-percent or less for liquid-line temperatures below approximately 110 F (43.3°C). For the R-22/naphthenic oil and R-502/alkylbenzene oil mixtures, an oil concentration measurement uncertainty of ±2 weight-percent was attained for liquid-line temperatures below aproximately 90 F (32.2°C).

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