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<p>The double-pipe heat exchanger remains one of the most widely used thermal systems due to its simple design, robustness, and ease of maintenance. However, its performance is often limited by the formation of viscous and thermal boundary layers along smooth surfaces. To overcome this drawback, surface modification through helical corrugation of the inner pipe has emerged as an effective passive enhancement technique. This review systematically evaluates recent progress in the thermal–hydraulic performance of helically corrugated inner pipes in double-pipe heat exchangers. Key geometric parameters—including corrugation pitch, height, and helix angle—are shown to directly influence flow patterns, turbulence intensity, and overall efficiency. Evidence from experimental, numerical, and theoretical studies demonstrates that reducing pitch and increasing height significantly improve heat transfer by intensifying swirl flow and boundary layer disruption, but at the expense of higher friction factors and pumping power. Similarly, variations in helix angle indicate that larger angles promote stronger secondary flows and higher Nusselt numbers, while smaller angles reduce hydraulic losses. Comparative analyses further reveal that external (convex) corrugations generally outperform internal (concave) ones by offering a better trade-off between heat transfer and pressure drop. Despite consistent improvements in the thermal performance factor, challenges remain in optimizing corrugation geometry, verifying the effect of corrugation shape, and validating large-scale applications. Future studies should also integrate nanofluids, hybrid enhancement techniques, and AI-based optimization to establish reliable design strategies.</p>

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Thermal improvement in double-pipe heat exchanger: Review of helical corrugated inner pipe case

  • 期刊论文

  • 发表日期：

    2026年5月28日

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  • Saif Ali Kadhim,
  • Ali M. Ashour,
  • Osama Abd Al-Munaf Ibrahim,
  • Moafaq K. S. Al-Ghezi,
  • Zaid Ali Hussein,
  • Abdallah Bouabidi,
  • Walid Aich

摘要

The double-pipe heat exchanger remains one of the most widely used thermal systems due to its simple design, robustness, and ease of maintenance. However, its performance is often limited by the formation of viscous and thermal boundary layers along smooth surfaces. To overcome this drawback, surface modification through helical corrugation of the inner pipe has emerged as an effective passive enhancement technique. This review systematically evaluates recent progress in the thermal–hydraulic performance of helically corrugated inner pipes in double-pipe heat exchangers. Key geometric parameters—including corrugation pitch, height, and helix angle—are shown to directly influence flow patterns, turbulence intensity, and overall efficiency. Evidence from experimental, numerical, and theoretical studies demonstrates that reducing pitch and increasing height significantly improve heat transfer by intensifying swirl flow and boundary layer disruption, but at the expense of higher friction factors and pumping power. Similarly, variations in helix angle indicate that larger angles promote stronger secondary flows and higher Nusselt numbers, while smaller angles reduce hydraulic losses. Comparative analyses further reveal that external (convex) corrugations generally outperform internal (concave) ones by offering a better trade-off between heat transfer and pressure drop. Despite consistent improvements in the thermal performance factor, challenges remain in optimizing corrugation geometry, verifying the effect of corrugation shape, and validating large-scale applications. Future studies should also integrate nanofluids, hybrid enhancement techniques, and AI-based optimization to establish reliable design strategies.