Thermodynamic design and simulation of a CO2 based transcritical vapour compression refrigeration system with an ejector

• A transcritical CO2 refrigeration cycle with an ejector is analyzed.
• Critical flow areas of 2 − ϕ ejector components are determined for design conditions.
• Thermodynamic system simulation is implemented using computed ejector dimensions.
• Exergy destruction in each of the components is estimated.
• Results indicate primary nozzle and mixing to be major sources of irreversibility.

A two phase ejector suitable as an expansion device in a CO2 based transcritical vapour compression refrigeration system is designed by extending the thermodynamic analysis and by interfacing with the system simulation model. A converging diverging nozzle is considered as primary nozzle of the ejector. For both design and parametric analyses, the efficiencies of nozzles and diffuser have been assumed to be 85% each. Further, choked condition in the primary C-D nozzle and constant pressure mixing are assumed. Parameters such as COP, entrainment ratio, pressure lift and cooling capacity were obtained for varying motive inlet and evaporator conditions. Motive inlet is found to be crucial for both performance and range of feasible application. Results show a COP improvement of 21% compared to an equivalent conventional CO2 system. A comprehensive exergy analysis of the system establishes the justification of replacement of throttle valve by ejector in such systems.