Mathematical modeling and thermodynamic investigation of the use of two-phase ejectors for work recovery and liquid recirculation in refrigeration cycles

• Comparison of two ejector uses: Direct compressor unloading, liquid recirculation.
• Different ejector cycles are investigated and compared using numerical models.
• High throttling loss fluids (CO2) should use ejector to directly unload compressor.
• Low-pressure fluids (R134a) should use ejector to recirculate liquid.
• Cycle COP not affected by ejector efficiency when using ejector for recirculation.

This paper presents the results of a numerical investigation on the performance of ejector cycles in which the work recovered is used to recirculate liquid through the evaporator. The ejector recirculation cycle, in which the ejector is only used to recirculate liquid and improve evaporator performance, and the standard ejector cycle, in which the ejector can be used to both recirculate liquid and directly unload the compressor, are investigated. The analysis uses a microchannel evaporator and refrigerants R134a, R410A, and CO2. It is seen that fluids that have large throttling loss but gain little benefit from liquid recirculation (CO2) should use the ejector to directly unload the compressor, while fluids that have lower throttling loss but gain significant benefit from liquid recirculation (R134a) should use the ejector to improve evaporator performance through liquid recirculation. It is also seen that the ejector recirculation cycle is better suited for ejector off-design operation.