ShareA new non-flammable mixture to boost the performance of CO2 systems
In a recent IJR article, researchers propose combining R744 with Dimethyl-ether (DME) to boost system performance while ensuring safety and low environmental impact, in a recent IJR article.
CO2 (R744) refrigeration systems are experiencing an increasing market share in commercial (i.e. retail) and industrial refrigeration, especially in Europe, North America and Japan. In Europe, the leading market, transcritical CO2 systems reached a 22.9% market share in the food retail sector in 2023, up from 18.4% the year before. (see previous IIR news)
This success is due to the increasing efficiency of CO2 systems. New attempts are done by researchers from academia and the industry to extend the range of applications to other sectors such as transport refrigeration. However, improvements often require increasingly complex refrigeration systems, for instance with the use of multiple ejectors.
Using fluid mixtures could be a worthwhile alternative towards the improvement of CO2-based systems. In a recent theoretical study published in the IJR, Vaccaro et al. evaluated several mixtures of CO2 and organic substances: propane (R290), iso-butane (R600a), dimethyl-ether (DME) and propylene (R1270).
The authors found that these mixtures may increase the COP of refrigeration cycles thanks to a reduction in compression work and an improved temperature matching between the evaporating working fluid and a finite-heat-capacity heat source. For instance, a mixture of CO2 with a 23% mass fraction of propylene offered a COP increase of 28%, while highly flammable, as were mixtures containing propane and iso-butane.
Vaccaro et al. found that a mixture of CO2 with 8% DME was non-flammable and resulted in a COP increase of 25% compared with pure CO2. This mixture would represent a safe option, combining the advantages of CO2 (low GWP, high volumetric cooling capacity) with good energy efficiency, reducing energy consumption by 25 %, even for a basic cycle comprising only an internal heat exchanger.
The authors evaluated the environmental impact of the mixture using the total equivalent warming impact (TEWI) metric. As DME has a GWP of 1, the direct emission term in the TEWI calculation for the CO2/DME mixture is negligible. Evaluated in a theoretical model, this promising finding still needs to be tested experimentally.
Scheduled to take place at the University of Maryland (USA) on August 11-14, 2024, the 16th IIR-Gustav Lorentzen Conference on Natural Refrigerants (GL 2024) will provide the ideal platform for discussion on the latest research results and advances related to the use of natural working fluids in different types of systems and application areas.
Find out more here.
Sources
Penetration of transcritical CO2 continues to increase. https://iifiir.org/en/news/penetration-of-transcritical-co2-continues-to-increase
Vaccaro G., Milazzo A., and Talluri L. "A proposal for a non-flammable, fluorine-free, CO2-based mixture as a low TEWI refrigerant." International Journal of Refrigeration 158 (2024): 157-163. https://iifiir.org/en/fridoc/a-proposal-for-a-non-flammable-fluorine-free-co-lt-sub-gt-2-lt-sub-gt-based-148404