Simulation and experimental evaluation of the effects of oil circulation in an inverter air conditioning system using R-22 and R-407C

A steady-state mathematical modeling and experimental study were carried out to investigate effects of oil circulation in an inverter air conditioner using R-22 and R-407C. To highlight the prediction of oil circulating mass fraction, the simplified sub-model of oil discharge was modified. The predicted results were validated with experimental data. Two tested lubricants were mineral oil (MO) and polyol-ester lubricant (POE). The experiments varied the compressor frequency in the range of 30–50 Hz for each compressor oil level (0.8 l and 1 l). The results showed that the circulating oil flow rates decreased with the reducing compressor frequency and with a lower oil charge. The lubricant concentration affected the system performance at high frequencies. The charged oil quantity of 0.8 l provided more efficient performance than 1 l. The vapor velocity of R-407C is inadequate high enough to entrain the liquid MO at its lowest frequency. The immiscible mixture of R-407C/MO is not suitable used in the inverter air conditioning system. The proposed model obtains better results for the miscible mixture. The model prediction agreed with the measured values in the compressor frequency of 40–50 Hz.