13. Air-Condition and Refrigeration

The mixing of refrigerant and refrigerant oil usually occurs in refrigeration compressors, which affects the viscosity and foaming of the oil. In particular, zeotropic refrigerants are composed of two or more components whose equilibrium vapor and liquid phases have different compositions. As a result, the mixing behavior of zeotropic refrigerant and oil is expected to be different from that of pure refrigerant. In this study, the zeotropic refrigerant and refrigerant oil used were R454C refrigerant and polyolester (POE) oil due to their good compatibility. To investigate the mixing characteristics of R454C and POE, a high-pressure and high-temperature resistant vessel with mounted transparent glass was used to conduct the experiment. The test conditions for the temperature and the refrigerant concentration in oil were varied during 30–90 °C and 0–100%, respectively. In addition, refractive index is one of the properties that changes following the mixing ratio of the oil and refrigerant mixture. Thus, in this experiment, a refractive index measurement was also employed to measure the mixing property by using an optical fiber sensor. This sensor has high accuracy and can be used under high pressure and temperature conditions. Finally, a relationship between the refractive index and the refrigerant concentration in oil was proposed depending on the temperature.