Experimental and numerical analysis of hydrothermal behavior for different nanofluids in a shallowly dimpled tube heat exchanger

Feb 26, 2026

Journal Environmental Progress & Sustainable Energy

DOI 10.1002/ep.70376

Issue Early View

Volume Early View

Heat exchangers require improved thermal efficiency for power generation, chemical processing, and electronics cooling applications. While dimpled surfaces and nanofluids have been studied separately, their combined implementation and synergistic mechanisms remain poorly understood. This study experimentally and numerically investigates aluminum oxide, copper oxide, and titanium dioxide nanofluids at 0.5%–2.0% concentrations in shallowly dimpled copper tubes. Hemispherical dimples with depth-to-diameter ratios of 0.1–0.3, diameters of 4–8 mm, and pitch-to-diameter ratios of 0.8–1.6 were tested across Reynolds numbers of 4000–20,000. Copper oxide nanofluid at 1.5% concentration in optimally configured dimpled tubes achieved 85.3% heat transfer enhancement compared to water in smooth tubes, with a thermal performance factor of 1.83. This substantially exceeded individual contributions of 34% for nanofluids alone and 38% for dimpled tubes alone, confirming strong synergistic effects. Flow visualization revealed dimple-generated vortices intensify nanoparticle microscale transport through simultaneous boundary layer disruption and enhanced thermal conductivity. Optimal configurations maintained 52% pressure penalties while nearly doubling heat transfer rates. Empirical correlations from 180 data points predicted performance within 7% accuracy. This research quantifies synergistic effects between geometric enhancement and nanofluid technology, provides validated design correlations, and elucidates underlying mechanisms, enabling next-generation compact heat exchangers for energy-intensive applications. This study presents a comprehensive investigation of heat transfer enhancement using various nanofluids in a novel shallowly dimpled tube heat exchanger. Experimental tests and computational fluid dynamics (CFD) simulations were conducted to analyze the hydrothermal behavior of Al₂O₃, CuO, and TiO₂ nanofluids at volume concentrations ranging from 0.5% to 2.0%. The dimpled tube geometry featured hemispherical dimples with pitch-to-diameter ratios of 0.8, 1.2, and 1.6, and dimple depth-to-diameter ratios of 0.1 to 0.3. Results demonstrated that the CuO nanofluid (1.5% concentration) in tubes with dimple depth-to-diameter ratio of 0.2 and pitch-to-diameter ratio of 1.2 achieved the highest thermal performance factor of 1.83, representing a 47.6% enhancement in heat transfer coefficient compared to pure water in smooth tubes. Flow visualization and numerical simulations revealed complex vortical structures generated by the dimples that promoted boundary layer disruption and enhanced fluid mixing. The enhancement mechanism was attributed to the combined effects of increased thermal conductivity from nanoparticles and improved convection from dimple-induced flow perturbations. A thermal-hydraulic correlation was developed that predicted performance within ±7% of experimental data across the tested Reynolds number range (4,000-20,000). This research provides new insights into optimizing heat exchanger designs by combining surface modifications with nanofluids for advanced thermal management applications.

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