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<p>Cooling high-viscosity lubricating oils in hydraulic machinery remains challenging due to severe performance degradation under low Reynolds number conditions. Conventional segmental baffle exchangers suffer from high form drag, while existing longitudinal flow designs fail to generate sufficient flow disturbance for highly viscous fluids. To address this critical gap, this study proposes a novel industrial-scale, self-supported heat exchanger with twisted trefoil tubes. The twisted trefoil tube features a three-lobed cross section (<i>D</i> = 6&#xa0;mm, <i>d</i> = <i>1</i>&#xa0;mm) with a twist pitch of 80&#xa0;mm. Its shell-side thermal–hydraulic characteristics were evaluated relative to conventional segmental baffle and twisted elliptical tube exchangers, using industrial lubricating oil with Reynolds numbers ranging between 80 and 550. Results indicate that the proposed design yields remarkable heat transfer enhancement. Its heat transfer coefficient is 138.7%–190.5% higher than that of the conventional segmental baffle exchanger and is 257.8%–298.6% higher than that of the twisted elliptical tube exchanger. Although the design produces a 19.6%–37.8% higher pressure drop compared with the conventional exchanger, its overall performance factor is respectively 77.2%–130.4% and 40.1%–65.7% higher than those of the two conventional counterparts. This enhancement is physically interpreted as the synergistic effect of three-dimensional longitudinal flow, secondary flows, and centrifugal forces, which disrupts the thermal boundary layer and induces an early transition to turbulent-like conditions. Empirical correlations for the Nusselt number and friction factor were developed based on the experimental data. This work provides experimental evidence that longitudinal flow designs can overcome laminar flow limitations without the need for baffles, offering an efficient solution for compact industrial oil cooling applications.</p>

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Thermal–hydraulic performance assessment of self-supported heat exchangers with deformation-enhanced tubes in low Reynolds number regime

  • 期刊论文

  • 发表日期：

    2026年6月15日

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  • Shijie Liu,
  • Yidi Sun,
  • Zhou Ye,
  • Aimin Tu,
  • Yingde Yin,
  • Dongsheng Zhu

摘要

Cooling high-viscosity lubricating oils in hydraulic machinery remains challenging due to severe performance degradation under low Reynolds number conditions. Conventional segmental baffle exchangers suffer from high form drag, while existing longitudinal flow designs fail to generate sufficient flow disturbance for highly viscous fluids. To address this critical gap, this study proposes a novel industrial-scale, self-supported heat exchanger with twisted trefoil tubes. The twisted trefoil tube features a three-lobed cross section (D = 6 mm, d = 1 mm) with a twist pitch of 80 mm. Its shell-side thermal–hydraulic characteristics were evaluated relative to conventional segmental baffle and twisted elliptical tube exchangers, using industrial lubricating oil with Reynolds numbers ranging between 80 and 550. Results indicate that the proposed design yields remarkable heat transfer enhancement. Its heat transfer coefficient is 138.7%–190.5% higher than that of the conventional segmental baffle exchanger and is 257.8%–298.6% higher than that of the twisted elliptical tube exchanger. Although the design produces a 19.6%–37.8% higher pressure drop compared with the conventional exchanger, its overall performance factor is respectively 77.2%–130.4% and 40.1%–65.7% higher than those of the two conventional counterparts. This enhancement is physically interpreted as the synergistic effect of three-dimensional longitudinal flow, secondary flows, and centrifugal forces, which disrupts the thermal boundary layer and induces an early transition to turbulent-like conditions. Empirical correlations for the Nusselt number and friction factor were developed based on the experimental data. This work provides experimental evidence that longitudinal flow designs can overcome laminar flow limitations without the need for baffles, offering an efficient solution for compact industrial oil cooling applications.