Thermodynamic analysis and optimization of a CO2 based transcritical refrigeration system with an ejector

In the present paper some results obtained from the thermodynamic analysis of a CO2 based transcritical refrigeration system are presented. The system studied uses an ejector as an expansion device in place of the conventional throttle valve. Results are obtained considering constant pressure mixing process in the mixing chamber of the ejector. The compressor discharge pressure and ejector entrainment ratio are optimized for maximum COP. The required compressor displacement rate per ton of refrigeration (specific piston displacement rate, PD) is calculated at the optimum conditions. A correlation is obtained for PD in terms of the evaporator, gas cooler exit and ejector efficiencies. From the sensitivity analysis it is seen that of all the parameters, the PD is most sensitive to evaporator temperature.