In industrial waste-heat recovery, double-tube heat exchangers are widely used owing to their structural adaptability and operational reliability. To enhance thermal performance, this study proposes a discontinuous high-low double helical fin double-tube heat exchanger and numerically investigates the effects of fin discontinuity distance, low-fin height, and helix angle on shell-side flow and heat transfer. The results indicate that periodic axial interruptions combined with alternating fin heights intensify turbulence and promote fluid mixing, thereby enhancing heat transfer. Response Surface Methodology is used to optimize the structural parameters, and the results show that the helix angle is the dominant factor, with a notable interaction with the fin discontinuity distance. Under the optimal conditions of a fin discontinuity distance of 142.5 mm, a low-fin height of 12.1 mm, and a helix angle of 59.3?, the optimized configuration increases the Nusselt number by 28.25%, reduces the friction factor by 9.68%, and improves the performance evaluation criterion by 38% compared with a conventional single helical fin configuration. These findings provide quantitative guidance for the design of high-efficiency double-tube heat exchangers.
Cao et al. (Thu,) studied this question.