Advances in Subcooling Techniques for Transcritical CO₂ Refrigeration Systems: A Comprehensive Review

Transcritical CO₂ refrigeration systems are increasingly adopted as low-GWP alternatives; however, their performance deteriorates due to high gas cooler pressures and large throttling losses. Subcooling the refrigerant before expansion is a key thermodynamic solution to mitigate these losses, yet a comprehensive and updated synthesis that directly compares the performance and applicability of diverse subcooling techniques within a unified framework is lacking. This review addresses that gap by providing a structured, critical analysis of both internal and external subcooling methods, including internal heat exchangers (IHX), ejector- and expander-assisted systems, and mechanical and thermoelectric subcoolers. The consolidated findings indicate that for high-ambient conditions, mechanical subcooling consistently emerges as the most effective approach, offering substantial COP improvements (۲۰-۴۰%) and in the case of DMS, significant discharge pressure reduction. This review further examines integration challenges, advanced control strategies, and emerging hybrid and renewable-assisted systems, offering valuable insights for researchers and designers aiming to enhance the sustainability and performance of next-generation CO₂ refrigeration technologies.

کلیدواژه ها:

subcooling ، transcritical co۲ ، integrated mechanical ، dedicated mechanical ، thermoelectric