Enhancing Heat Exchanger Performance through Passive Techniques: A Comprehensive Review

Heat exchangers play a crucial role in thermal energy systems, with their performance directly impacting efficiency, cost, and environmental impact. A powerful technique for performance improvement can be given by passive enhancement strategies, which are characterized by their dependability and minimal external power requirements. This comprehensive review critically assesses recent advancements in such passive methods to evaluate their heat transfer mechanisms, performance characteristics, and practical implementation challenges. Our methodology involves a systematic and comprehensive analysis of various heat transfer enhancement techniques, including surface modifications, extended surfaces, swirl flow devices, and tube inserts. This approach synthesizes and integrates findings from a broad spectrum of experimental investigations and numerical simulations to establish a cohesive understanding of their performance characteristics and underlying mechanisms. Based on the findings, passive heat transfer techniques result in significant improvements in thermal performance; for instance, corrugated and roughened surfaces increase the heat transfer coefficient by 50%–200%, and advanced insert geometries, such as modified twisted tapes, can increase it by more than 300%, typically accompanied by significant pressure-drop penalties. However, an important finding is the general trade-off between enhanced heat transfer and higher frictional loss, which requires optimization depending on the applications. Finally, this review also provides recommendations that will document the gaps of various passive techniques in heat exchangers to future address.