DOI: 10.17632/p8z3d7zhht
title: An analysis of a use of an environmentally friendly natural working fluids mixture based on carbon dioxide (R744) in modern ejector-based refrigeration cycles: simulations data

description: The synthetic refrigerant replacement by a low-GWP or blend with natural working fluids to reduce GWP [1] is the current challenge, but the use of new refrigerants, i.e., HFO, affects the poisoning of water, e.g. groundwater, and may be harmful to human health [2]. As a result of the harmfulness of synthetic working fluids, it is necessary to use ecological refrigerants in applications characterised by low coefficient of performance (COP), i.e., low and ultra-low freezing in the range of -50 ° C to -20 ° C used in food transport, freeze drying and storage of food products [3]. In Poland, almost 5 million tons of food is wasted annually at the stages of production, processing, distribution and consumption [4]. Therefore, the only safe and necessary solution in the food industry and to reduce losses in the food chain is to use a mixture of natural refrigerants, i.e. R744, or hydrocarbons, due to thermodynamic properties, availability and no negative impact on the environment [1]. The mixture of natural working fluids will expand the scope of application of cooling systems in low- and high-temperature areas, although in order to maintain a high COP, it is required to use state-of-the-art technologies in the refrigeration system, i.e., a two-phase ejector. The main purpose of the ejector operation in the system is to partially recover of the expansion work, which results in a higher efficiency of the entire system (even by 25%), as well as lowering the pressure ratio in the compressor, reducing the total energy consumption at a properly designed new generation ejector [5]. 

The main aim of the work was to investigate the effect of the use of a two-phase ejector on the flow behavior and thermodynamic effects of environmentally friendly and non-flammable mixtures of natural working fluids based on carbon dioxide and propylene in refr. systems at low temperature processes. As a result, the current limitations of refrigeration cycles based on single-component natural refrigerants will be removed to shorten the food chain, reduce food waste and improve the energy efficiency of food storage processes in the food industry. Minimizing losses in the food chain is essential to reducing the global and local problem of food waste. This design goal is especially important during phasing out of synthetic refrigerants and introducing low-impact working fluids into all refr. systems. 


Acknowledgment: Project No. 2021/05/X/ST8/00266 funded by Polish NCN.

References:
[1] N. Abas et al., Nat. &  synth. refrigerants, global warming: A rev. Ren. & Sust. En. Rev., 2018
[2] Refolution Industriekälte GmbH, Report and statement of the downsides of HFO refrigerant usage, 2021.
[3] S.J. James, C. James, The food cold-chain and climate change. Food Res. Int., 2010.
[4] Federacja Polskich Banków Żywności, Raport “Nie marnuj jedzenia 2020”, 2020.
[5] J. Bodys et al., Exp. and num. study on the R744 ejector with a suction nozzle bypass, Appl. Therm. Eng., 2021.