Quantitative comparison of the performance of vapor compression cycles with compressor vapor or liquid injection

Increasing the Coefficient of Performance (COP) of vapor compression cycles has been a major focus for decades. Significant improvements can be brought by modifying multistage compressor to flooded single-stage compressor to approach isothermal compression. This work presents the comparative analysis of the cycle performance of a flash tank economized system (FTES), multiple refrigerant injection system (MRIS) and an oil flooded system (OFS). Thermodynamic models of each of these systems using ideal mixing models of refrigerants with the flooding agents are presented. Additionally, mixing effectiveness is introduced as a metric to evaluate the non-ideal mixing of the OFS. Results show that in MRIS, an increase in the number of injection ports significantly increases the COP of the cycle between 18% and 51% for air conditioning and refrigeration applications. The OFS shows that increasing the oil mass flow rate increases the COP significantly above the baseline cycle, benefiting higher temperature lift applications. At evaporating temperature of -40 degrees C, relative COP for MRIS with 2 injection points is 7.5% higher than FTES and 5.0% higher than OFS. Further, quantification of the influence of the non-ideal mixing model for OFS showed that a mixing effectiveness of 80% results in 21% degradation of system COP suggesting the ideal mixing assumption has significant influence on the potential for an OFS.