Introduction
Energy recovery systems, such as heat sinks, heat exchangers, and condensers, are very important in improving the overall process efficiency of different thermal energy systems. Among these devices, many operate under low to moderate Reynolds numbers, where thermal performance becomes limited due to weak mixing, boundary-layer growth, and reduction of temperature gradients. Several conventional performance enhancement techniques are incorporated, such as active mixing, surface treatments, inserts, etc. However, these strategies increase system complexity, pressure drop, or energy consumption, thereby offsetting the benefits.
In this context, simple geometric design innovations prove crucial in enhancing heat transfer using passive modes [1]. Helical geometries can be employed to improve fluid mixing and heat transfer owing to their curvature-driven secondary flow features (Dean vortices) [2]. Despite their simplicity and inherent compactness, certain aspects are less-explored, particularly how specific geometric modulations can be systematically mapped to different dominant thermal resistances across applications. Furthermore, these geometries offer potential as transferable, general-purpose design guidelines rather than case-specific enhancements, for various energy systems. The present work synthesizes and reinterprets isolated helical-geometry studies applied to three representative applications, a (i) heat sink, (ii) cross-flow heat exchanger, and (iii) conical coil condenser, to establish a unified design framework based on the spatial tuning of s curvature-induced feature. The aim of this work is to demonstrate a common passive geometric principle that can be achieved by adjusting geometric parameters, and leveraged across different energy systems to achieve scalable and mechanism-informed performance enhancement.
Methods
This study is based on validated CFD simulations, which are carried out for three distinct thermal systems employing helical geometries. In all cases, steady-state, laminar flow conditions are considered, which are representative of compact thermal energy systems. Working fluids and boundary conditions were selected to demonstrate application-relevant operating conditions relevant for each application. For heat sink configuration, helical fins were employed to enhance coolant-side heat removal, and relate flow intensification with thermal performance [3]. In a cross-flow heat exchanger, interaction between internal helical flow and external cross-flow was examined to evaluate heat transfer rate and efficiency [4]. For the condenser, both simple helical and conical helical coils of equal tube length were analysed to investigate the influence of cone angle on secondary flow development and heat extraction along the flow path. In all cases, the analysis mainly focuses on flow fields, temperature fields, and non-dimensional heat transfer metrics. Improvements in heat transfer were found to primarily be the effect of curvature-induced secondary flow intensification.
Results
All the systems showed a common underlying enhancement mechanism, governed by helical geometry, even though there are differences in applications. Centrifugal forces generated due to curvature lead to the formation of secondary flow structures, which result in the enhanced transverse mixing and disruption of thermal boundary layers. In the heat sink configuration, swirl-induced natural convection results in reduced surface temperature non-uniformity and enhanced fin efficiency by 10-15%. The cross-flow heat exchanger demonstrates improved Nu (1.4 to 2.5 times) and heat exchanger efficiency up to 90% due to flow intensification and tortuosity. In the condenser system, geometric modification through conical design led to progressive intensification of secondary flow, which compensates for decreasing temperature gradients, resulting in an overall heat extraction enhancement of ~14%. Cross-comparison of these applications shows that, although the dominant thermal limitations are different, as poor mixing in heat sinks, boundary-layer growth in heat exchangers, and temperature gradient decay in condensers, the helical design principle consistently mitigates these limitations through a common passive mechanism [5], and highlights the versatility of helical-geometry-based enhancements.
Conclusions
Implementation of helical configurations serve as an effective and broadly applicable design strategy for enhancing thermal energy recovery. By intensifying secondary flow, simple helical geometries are shown to improve heat transfer, in a passive manner, without increasing complexity and energy consumption. This analysis, covering a heat sink, cross-flow heat exchanger, and condenser, emphasizes the potential of geometry-driven design innovations in a unified, cross-application framework. The findings provide generalized and transferable design insights that can be used for the development of next-generation passive energy devices for compact industrial and environmental applications.
References
[1] M.A. Rahman, Review on heat transfer augmentation in helically coiled tube heat exchanger, International Journal of Thermofluids 24 (2024). https://doi.org/10.1016/j.ijft.2024.100937.
[2] J.O.D.B. Lira, H.G. Riella, N. Padoin, C. Soares, Fluid dynamics and mass transfer in curved reactors: A CFD study on Dean flow effects, J. Environ. Chem. Eng. 10 (2022). https://doi.org/10.1016/j.jece.2022.108304.
[3] V.K. Jha, S.K. Bhaumik, Enhanced heat dissipation in helically finned heat sink through swirl effects in free convection, Int. J. Heat Mass Transf. 138 (2019) 889–902. https://doi.org/10.1016/j.ijheatmasstransfer.2019.04.099.
[4] V.K. Jha, S.K. Bhaumik, Enhanced cooling in compact helical tube cross-flow heat exchanger through higher area density and flow tortuosity, Int. J. Heat Mass Transf. 150 (2020) 119270. https://doi.org/10.1016/j.ijheatmasstransfer.2019.119270.
[5] V.K. Jha, K. Banerjee, S.K. Bhaumik, Enhanced thermal stability of novel helical-finned jacketed stirred tank heater, Appl. Therm. Eng. 184 (2021). https://doi.org/10.1016/j.applthermaleng.2020.116250.
