Impact of Oil Solubility and Refrigerant Flashing on the Performance of Transcritical CO2 Vapor Compression Systems with Oil Flooding and Regeneration

Flooding the compressor of a vapor compression system with oil can allow for a more isothermal compression process. This can lead to significant improvements in performance, particularly when combined with a regenerative heat exchanger. For CO2 cycles with supercritical heat rejection, the superheat horn and throttle are major sources of irreversibility. The combination of flooding and regeneration attacks both of these losses with a relatively small impact on system costs. The improvement in system COP can be over 20% for sink and source temperatures of 30°C and -30°C, respectively, with an optimized oil mass fraction and oils that have low refrigerant solubility. However, when some amount of refrigerant is solved in the oil, the cooling capacity is decreased. At a refrigerant solubility of 20% by mass in the oil for fixed oil mass fraction, there is no improvement in system COP compared to the baseline system.