Advanced exergy analysis of a Reverse Brayton cycle using air as working fluid for cryogenic purposes

Abstract

[EN] The global push to reduce greenhouse gas emissions has led to the ban of high global warming potential (GWP) refrigerants in the refrigeration sector, prompting the adoption of low-GWP alternatives. However, as regulations are expected to tighten, technologies like the Reverse Brayton cycles (RBC) are emerging. RBCs can operate with safe fluids and can reach very low temperatures through compressions, regeneration, and expansion, requiring only electricity. This research presents results from an RBC equipped with a radial turbine using natural air (R-729), a hazard-free fluid with zero ozone depletion potential (ODP) and emission potential. The cycle utilizes automotive components, offering a cost-effective, high-tech solution. The study evaluates the cycle COP at a design point and performs an exergetic analysis at 173K. Using a thermal and fluid dynamic model of the cycle, the critical components of the cycle influencing the COP are identified, and potential improvements are explored.