Effect of twisted tapes with multiple rotating turbulators on the performance of a double-pipe heat exchanger

Critical to many applications, heat exchangers are widely used across industries such as air conditioning, refrigeration, and power plants. This has led to a renewed focus on improving their efficiency through active and passive techniques. This study employs a passive technique (twisted tape and twisted tape combined with rotating turbulators) to investigate the thermal and frictional performance of a double-pipe heat exchanger. Experiments were conducted with water as the working fluid over a Reynolds number range of 5500 to 10,000, and varying numbers of rotating turbulators (1–6). The addition of rotating turbulators at a vane angle of 30° increased heat transfer by up to 118% compared to the plain tube, with the optimal configuration being 3 turbulators which achieved a balance between heat transfer and frictional losses. These enhancements are attributed to combined primary and secondary swirl flows, though friction factors increased up to 3.63 times for 6 turbulators. The performance evaluation criterion highlighted that twisted tape with turbulators is most effective at lower Reynolds numbers, with reduced efficiency at higher Reynolds numbers due to frictional losses. Regression analysis yielded highly accurate correlations for Nusselt number (R 2 = 0.9865) and friction factor (R 2 = 0.9609), with predicted values deviating within ±10% of experimental results. This research contributes to Sustainable Development Goal 7 (Affordable and Clean Energy) by improving energy efficiency through enhanced heat transfer, and Goal 9 (Industry, Innovation, and Infrastructure) by advancing heat exchanger design. These findings offer critical insights for designing high-performance heat exchangers in HVAC, energy, and process industries.