A comprehensive review on heat transfer enhancement in tubular heat exchangers using twisted tapes, wire coil inserts, and their combined effect with nanofluids

Enhancing heat transfer is crucial for reducing energy consumption and costs, providing substantial economic and environmental benefits. Heat transfer improvement techniques are commonly applied to optimize heat exchanger performance or reduce their size and weight. These techniques fall into two categories: active and passive. Active techniques rely on external power, whereas passive techniques function without it. This review focuses on passive techniques, particularly twisted tape inserts, which are easy to manufacture and integrate into existing systems. Twisted tapes enhance convective heat transfer by inducing a swirling motion in the flow and disrupting the boundary layer at the tube surface through periodic changes in surface geometry. Compared to active methods, passive techniques offer significant advantages, including simplicity and efficiency. The study examines twisted tape as an insert using both numerical and experimental techniques, highlighting two of its key advantages—handling ease and retrofit possibility. This paper is broadly divided into two sections: active techniques and passive techniques. The passive techniques are further categorized into four main sections: twisted tape, self-rotating twisted tape, wire coil inserts, and the use of nanofluids and hybrid nanofluids in combination with twisted tapes. This review article also presents a comparative analysis of twisted tapes with self-rotating tapes, wire coils, and twisted tapes combined with nanofluids/hybrid nanofluids. It demonstrates that the application of nanofluids with twisted tapes yields superior results compared to the other methods. Finally, the paper provides recommendations for future research directions to further advance this field of study.