IIR document

Low temperature subcritical refrigeration cycles working with CO2 mixtures.

Number: 0222

Author(s) : SOBIERAJ M.


Carbon dioxide (R744) being an environmentally-friendly substance is widely used in refrigeration cycles. However, the use of CO2 is usually limited to the triple point temperature of -56.5°C. Below this temperature, only solid and vapour is present making R744 unsuitable as a direct replacement for Trifluoromethane (R23) with a high Global Warming Potential (GWP) value of 14800. No safe substitutes of R23 exist at the moment. For this reason, it is now of a great importance to take advantage of the unique thermophysical properties of CO2 and make it usable below triple point temperatures. This paper presents experimental characteristics of subcritical refrigeration cycle set-up designed and built at the Faculty of Building Services, Hydro and Environmental Engineering at Warsaw University of Technology. Experimental and theoretical analysis of a subcritical autocascade refrigeration cycle were performed, including exergy analysis, to examine the system efficiency in the search for an optimal high-boiling point (HBP) component to be used along with CO2 as a zeotropic mixture. Optimal compositions of each of the four examined zeotropic mixtures were calculated based on the internal exergy losses. Natural refrigerants R600 and R600a were found to reduce the exergy loses, providing the highest efficiency. Evaporation temperatures below the triple point of pure CO2 were achieved.

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Pages: 13 p.


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  • Original title: Low temperature subcritical refrigeration cycles working with CO2 mixtures.
  • Record ID : 30029791
  • Languages: English
  • Subject: Technology
  • Source: 15th IIR-Gustav Lorentzen Conference on Natural Refrigerants (GL2022). Proceedings. Trondheim, Norway, June 13-15th 2022.
  • Publication date: 2022/06/13
  • DOI: http://dx.doi.org/10.18462/iir.gl2022.0222
  • Document available for consultation in the library of the IIR headquarters only.


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