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

Articles in Press

Document Type : Review Article

Authors

1 Senior Research Engineer, R & D Cell, Cool-Max Innovations, Bhiwadi, rasasthan, India

2 Assistant Professor, Department of Mechanical Engineering, RKGIT Ghaziabad, Uttar Pradesh, India

3 Assistant Professor, NCE Chandi, Bihar

4 Aliah University Kolkata, West Bengal, India

Abstract

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 (20-40%) and in 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.

Keywords

Main Subjects

Journal of Heat and Mass Transfer Research

Articles in Press, Accepted Manuscript
Available Online from 16 April 2026

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History

  • Receive Date: 23 October 2025
  • Revise Date: 05 February 2026
  • Accept Date: 16 April 2026

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