Hybrid Enhancement of Heat Exchanger Efficiency via Geometric Modifications and Nanofluid-Induced Thermal Property Improvement

This study numerically investigates the combined heat transfer and fluid flow behavior in a double-pipe heat exchanger enhanced with spring-shaped turbulators and Al₂O₃ nanofluids. Four configurations are analyzed: circular turbulators (Case A), elliptical turbulators (Case B), circular turbulators with nanofluids (Case C), and elliptical turbulators with nanofluids (Case D), all compared against a smooth-pipe baseline. A validated ۳D CFD (Computational Fluid Dynamics) model implementing the realizable k-ε turbulence model (y+ ≈ ۱) and second-order discretization evaluates key parameters, Nusselt number, friction factor, and thermal performance across Reynolds numbers (۳,۰۰۰ ≤ Re ≤ ۲۰,۰۰۰). Results demonstrate that elliptical turbulators (Case B) outperform circular designs by ۱۲–۴۵% in heat transfer enhancement, with peak improvements (۴۸.۷%) at Re = ۳,۰۰۰, attributed to stronger secondary flows. Nanofluid addition further augments performance, particularly in laminar-transitional regimes, with Case D achieving the highest thermal efficiency. However, enhancements diminish at higher Re (>۱۳,۱۰۰) as natural turbulence dominates. Pressure drops, penalties increase by up to ۲۱۱.۴۶ Pa (Case D at Re = ۲۰,۰۰۰), highlighting a critical trade-off between heat transfer and hydraulic losses. ۳D thermal contours reveal that elliptical turbulators create ۲۵–۳۰% larger high-efficiency zones, while nanofluids reduce radial temperature gradients by ۳۵–۴۰%. Streamline analysis shows negligible global flow differences, confirming that improvements stem from localized near-wall effects. Exergy analysis indicates ۲۴% higher irreversibility for Case D at low Re, emphasizing thermodynamic trade-offs. For industrial applications, Case D is recommended for low-flow systems (Re < ۶,۲۰۰), while simpler designs suffice at higher Re. This work provides actionable insights for optimizing heat exchanger performance through combined geometric and nanofluid enhancements, validated by rigorous numerical and experimental benchmarks.

کلیدواژه ها:

Double-pipe heat Exchanger ، Spring Turbulators ، Nanofluids ، CFD ، Thermal-Hydraulic performance