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<p>The energy efficiency of heat exchangers can be enhanced by integrating passive methods, such as tubular fin turbulators, nanofluids, and helical coil tubes. This study experimentally investigates the synergistic effects of tubular fin turbulators in conjunction with two types of nanofluids: graphene oxide (GO) and alumina (Al<sub>2</sub>O<sub>3</sub>) focusing on the heat transfer characteristics of a helically wrapped coil-in-shell heat exchanger (CSHE). The experiment uses three distinct helically wound coils and is conducted at a constant heat flux of 4&#xa0;kW m<sup>−2</sup>. Two of the coils are equipped with tubular fins brazed to their outermost annular surfaces at orientations of <i>α</i> = 45° and 90°, while the third coil is a plain design without fins. The GO and Al<sub>2</sub>O<sub>3</sub> nanofluids are used at volume concentrations of 0.05, 0.10, and 0.15%, flowing through the coil side under laminar to turbulent flow conditions (500 ≤ Re ≤ 5500). The shell-side fluid is hot air, with velocities ranging from 1 to 5&#xa0;m s<sup>−1</sup>. Empirical data indicate that both nanofluids significantly enhance heat transfer in a finned coil-in-shell heat exchanger (FCSHE). The FCSHE exhibited a considerable increase in heat transfer compared to the unfinned CSHE using water at a moderate shell-side velocity of HAV = 3&#xa0;m s<sup>−1</sup>. At a volume concentration of 0.15%, the Nusselt number increased by 60.33% with GO and by 69.62% with the Al<sub>2</sub>O<sub>3</sub> nanofluid. Furthermore, under identical operating conditions, the combination of the 45°-oriented tubular fin and the 0.15% Al<sub>2</sub>O<sub>3</sub> nanofluid demonstrated an 8.90% greater enhancement in the Nusselt number indicating superior thermal performance compared to the finned CSHE–GO nanofluid combination with nominal pumping power loss. Additionally, the thermo-hydraulic performance (THP) factor nearly doubled when combining the Al<sub>2</sub>O<sub>3</sub> nanofluid with the 45° tubular fin orientation. In the end, the Nusselt number, friction factor, and THP values in both laminar and turbulent regimes showed reasonable agreement with permissible limits of ± 10– ± 14% between empirical and predicted outcomes.</p> Graphical Abstract <p></p>

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Experimental comparison and correlation development for synergistic heat transfer enhancement using GO and Al2O3 nanofluids with fin turbulator in coil-in-shell heat exchangers

  • 期刊论文

  • 发表日期：

    2026年1月9日

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  • Niranjana Rai,
  • Ramakrishna N. Hegde,
  • H. M. Shankara Murthy

摘要

The energy efficiency of heat exchangers can be enhanced by integrating passive methods, such as tubular fin turbulators, nanofluids, and helical coil tubes. This study experimentally investigates the synergistic effects of tubular fin turbulators in conjunction with two types of nanofluids: graphene oxide (GO) and alumina (Al2O3) focusing on the heat transfer characteristics of a helically wrapped coil-in-shell heat exchanger (CSHE). The experiment uses three distinct helically wound coils and is conducted at a constant heat flux of 4 kW m−2. Two of the coils are equipped with tubular fins brazed to their outermost annular surfaces at orientations of α = 45° and 90°, while the third coil is a plain design without fins. The GO and Al2O3 nanofluids are used at volume concentrations of 0.05, 0.10, and 0.15%, flowing through the coil side under laminar to turbulent flow conditions (500 ≤ Re ≤ 5500). The shell-side fluid is hot air, with velocities ranging from 1 to 5 m s−1. Empirical data indicate that both nanofluids significantly enhance heat transfer in a finned coil-in-shell heat exchanger (FCSHE). The FCSHE exhibited a considerable increase in heat transfer compared to the unfinned CSHE using water at a moderate shell-side velocity of HAV = 3 m s−1. At a volume concentration of 0.15%, the Nusselt number increased by 60.33% with GO and by 69.62% with the Al2O3 nanofluid. Furthermore, under identical operating conditions, the combination of the 45°-oriented tubular fin and the 0.15% Al2O3 nanofluid demonstrated an 8.90% greater enhancement in the Nusselt number indicating superior thermal performance compared to the finned CSHE–GO nanofluid combination with nominal pumping power loss. Additionally, the thermo-hydraulic performance (THP) factor nearly doubled when combining the Al2O3 nanofluid with the 45° tubular fin orientation. In the end, the Nusselt number, friction factor, and THP values in both laminar and turbulent regimes showed reasonable agreement with permissible limits of ± 10– ± 14% between empirical and predicted outcomes.

Graphical Abstract