Heat Transfer Augmentation in Multi-Tube Heat Exchangers for Decarbonization: Optimizing Straight/Helical Fin

Abstract Pursuing high-efficiency thermal systems demands innovative heat exchanger designs that balance superior heat transfer with manageable pressure losses. This study leverages ANSYS Fluent R1 2025 to conduct a comprehensive computational fluid dynamics (CFD) analysis of annular pipes equipped with straight and helical fins, evaluating their thermofluidic performance across Reynolds numbers (Re = 3500–7500). The double helical fins achieve unprecedented heat transfer enhancement (Nu +160%, Colburn j-factor +131%) but incur significant pressure penalties (ΔP +191%), while five straight fins offer a balanced compromise (Nu +92%, ΔP +63%). Optimizing triple-tube heat exchangers could reduce global CO2 emissions by up to 1.3 Gt/year with full adoption of helical fins-equivalent to the emissions from 300 coal plants-while straight fins enable quicker early-stage benefits. Estimates are based on a 10-year lifespan, 50°C ΔT, and 2.1 million industrial units. Through turbulence intensity (TI) mapping and grid-independent validation, the study reveals that helical fins generate swirl-dominated TI up to 20%, driving thermal gains but exacerbating energy costs. The double helical fin demonstrates the highest thermo-hydraulic performance, achieving a Figure of Merit (FoM) of 1.25–1.29, corresponding to an improvement of up to 29% over smooth tubes due to strong swirl-induced secondary flows. The 5-straight-fin configuration shows comparable performance (FoM: 1.20–1.23), offering substantial heat-transfer enhancement with a moderate pressure-drop penalty, consistent with trends reported for optimally finned annular passages in the literature, Webb and Kim, 59. The single helical fin provides moderate gains through Dean-vortex-driven mixing Naphon and Wongwises, 46, while the 3-straight-fin arrangement yields only marginal improvement, making it suitable for applications where low-pressure loss and energy efficiency are prioritized. The findings hold significant relevance for developing compact heat exchangers aimed at decarbonization, where maximizing energy recovery while minimizing pumping costs is essential for sustainable thermal system design.