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Start date: 2020Subject: search.filters.subject.Nusselt number

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    Numerical study of curved pin-fin cross-sections for enhanced thermal–hydraulic performance in microchannel cooling
    (2026-04-01)
    Kaewchoothong, Natthaporn
    ;
    Oo, Ye Min
    ;
    Gonsrang, Sarawut
    Efficient heat dissipation is crucial for modern high-heat-flux systems, where microchannel cooling offers compactness and high surface–area density. This study numerically investigated the thermal–hydraulic performance of air-cooled microchannels equipped with curved pin-fins featuring four cross-sectional shapes: a smooth circular baseline (C1) and multi-convex profiles containing 2, 3, and 4 lobes (C2–C4). Simulations were performed for Reynolds numbers of 200–1000 under uniform heat flux applied to both the endwall and fin surfaces, and the resulting flow structures, heat-transfer behavior, and pressure losses were evaluated using local and area-averaged Nusselt numbers, friction factors, and thermal-performance factors ( TPF ). The results showed that introducing cross-sectional convexity substantially modified the internal flow by enhancing impingement, strengthening secondary vortices, and suppressing wake regions. Among the tested designs, the two-convex geometry (C2) showed the greatest heat-transfer enhancement, whereas the three-convex configuration (C3) provided the most favorable thermal–hydraulic balance and consistently yielded the highest TPF . These findings clarified the governing mechanisms associated with curvature-induced mixing and demonstrated how tailored cross-sectional shaping can improve energy efficiency in microchannel-based cooling systems. The work provided practical geometric guidelines for advanced thermal management in battery modules, compact heat exchangers, and high-power electronics.
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    Influence of Delta Winglets on Improving heat transfer and friction factor characteristics in tubular heat exchanger
    (2025-05-19)
    Ruengpayungsak, K.
    ;
    Samruaisin, P.
    ;
    Kaewkosum, P.
    ;
    Pingta, S.
    ;
    Wongcharee, K.
    Heat transfer rate and pressure drop characteristics are two critical constraints that substantially influence the advancement of solar air heaters. The thermal efficacy of these systems is significantly improved by factors such as flow configurations, thermal mechanisms, and geometric modifications. The integration of insertion in turbulators is a common method to improve heat transfer efficiency in solar air heaters. This article presents heat transfer and thermal efficiency in a tubular heat exchanger incorporating Delta winglet (DW). The thermal transfer and pressure drop of air as a working fluid in a tube with a constant heat flux were quantified for Reynolds numbers (Re) between 6000 and 20,000. The DW elements were positioned on two tape sides in a configuration with attack angles (θ) of 30°, 45°, and 60°. Delta winglet height ratios (h/D=0.10) and pitch ratios (p/D=0.1) were examined. Data from the current smooth or plain tubes were also analyzed for comparative purposes. According to the experimental results, the tube with this inserted has a much higher Nusselt number (Nu) and friction factor (f) than a plain tube. Both Nu and f increase as θ decrease. The DW enhances Nu and f by approximately 2.51-3.04 times and 5.21-7.16 times, respectively. The maximum TEF of 1.34 is achieved at an attack angle of 30° and a Reynolds number of 6000. The statistical correlations for Nu f and TEF were analysed and demonstrated a strong fit to the observed data, with discrepancies of ±4%, ±5% and ±3%, respectively. This design improves the conservation of energy in heat exchanger tube applications.
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    Effect of arc-shaped twisted-baffles on augmented heat transfer in a rectangular duct
    (2023-02-01)
    Promvonge, Pongjet
    ;
    Phila, Arnut
    ;
    Chuwattanakul, Varesa
    ;
    Chokphoemphun, Suriya
    ;
    Eiamsa-Ard, Smith
    In this current work, the effect of utilizing arc-shaped twisted-baffles (T-ABs) in a rectangular air channel on thermal performance factor (TPF) has been experimentally studied. In these experiments, the influence of the changes in parameters such as dimensions of pitch ratio (p/w), attached arc-shape angle (α), and Reynolds number (Re) are explored. The comparisons demonstrate that a channel mounted with arc-shaped twisted-baffles yielded considerably greater Nusselt numbers than a smooth channel, possibly attributable to multiple-impinging jets near the channel surface. Heat transfer enhancements of twisted arc-shaped baffles (T-AB) having larger attack angles were superior to those having smaller attack angles. The one with α = 90o offered greater heat transfer rates than the ones with α = 20o, 40o, 60o, and 80o by approximately 8%, 7%, 4%, and 2%, respectively. The superior heat transfer was attributed to the better contact between the working fluid and heat transfer surfaces. In addition, utilizing arc-shaped twisted-baffles with the lowest p/w of 4.0, in a channel produced stronger vortices and multiple impinging jets, which caused better fluid mixing than other p/w. The optimum condition is achieved using T-ABs at an attached arc-shape angle of α = 90o, p/w = 4.0 and Re = 4000, where the heat transfer rate (Nu), friction factor (f) and TPF are found to be, respectively, 3.31, 4.68 and 1.98 times greater than those of a plain channel.
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    HEAT TRANSFER AND FLOW PROFILES IN ROUND TUBE HEAT EXCHANGER EQUIPPED WITH VARIOUS V-RINGS
    (2022-01-01)
    Boonloi, Amnart
    ;
    Jedsadaratanachai, Withada
    This study numerically investigates pressure loss, heat transfer and thermal efficiency in round tube heat exchangers attached with various types of V-rings. A typical type A V-ring is compared with two types of modified V-rings (type B and C). The impacts of blockage ratios, b/D = 0.05, 0.10, 0.15 and 0.20 for all V-ring types in the turbulent region are discussed (Re = 3000 – 20,000). Flow directions in the round pipe attached with the V-rings are varied. The V-apex setting downstream is referred to as “V-Downstream, while the V-apex setting upstream is referred to as “V-Upstream”. The flow and heat transfer profiles in the tested section are analyzed using the finite volume method (a commercial code with the SIMPLE algorithm). The thermal performance of the tested tube is measured in terms of dimensionless variables: thermal enhancement factor (TEF), Nusselt number (Nu) and friction factor (f). Numerical results reveal that type B and C V-rings can reduce pressure drop compared with type A V-ring. Additionally, the V-Upstream of type C V-ring yields the maximum TEF of 3.10 at b/D = 0.05.