IIR document

Regeneration of expansion energy by ejector in CO2 cycle.


In the transcritical CO2 cycle, regenerating expansion energy and increasing refrigerant pressure by means of an ejector is an effective way of improving the COP. The structure of the ejector is simple since the ejector is a non-volumetric type hydraulic pump and has no moving parts. In addition, the ejector simplifies the process of controlling the gas cooling pressure in the CO2 cycle. In this study, the COP improvement by employing an ejector cycle was compared with that for an expander cycle for ideal and realistic cases. Furthermore, an experiment was carried out in order to verify the potential of COP improvement. When the COP improvement of the ejector cycle was compared to that of the expander cycle under the condition that the recovered expansion power was used ideally, the ejector cycle provides the COP improvement less than half of that the expander cycle can provide. This was due to the unavoidable losses caused by the irreversible mixing in the mixing section of the ejector. However, if the efficiency of the ejector was taken into consideration, the COP improvement of the ejector cycle was equal to, or better than, that of the expander cycle. As for the flow in the nozzle the flow of refrigerant reaches supersonic inside the nozzle. The critical flow rate of the CO2 coincided with the value calculated by the isentropic homogeneous equilibrium model. The gas cooling pressure of the CO2 cycle could be controlled by changing the throat area of the nozzle. Finally, the experiment using the ejector in the car air-conditioner verified the COP improvement of approximately 20%.

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Pages: 2004-2


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  • Original title: Regeneration of expansion energy by ejector in CO2 cycle.
  • Record ID : 2007-1940
  • Languages: English
  • Source: Natural Working Fluids 2004: 6th IIR-Gustav Lorentzen Conference
  • Publication date: 2004/08/01


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