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    Item type:Publication,
    Heat transfer performance evaluation of a solar air heater duct with multiple tapered V-baffles
    (2025-12-01) ;
    Kaewkosum, P.
    ;
    Woncharee, K.
    ;
    Keaitnukul, W.
    ;
    Maruyama, N.
    This report aims to study the heat transfer enhancement, pressure loss characteristics, and thermal performance of a channel equipped with multiple tapered V-shaped baffles (MTVBs). The effects of up-facing and down-facing orientations, converging (C) and diverging(D) configurations, variations in the taper ratio (e<inf>CR</inf> and e<inf>DR</inf> = 0.0 and 0.5), and Reynolds number (6000 ≤ Re ≤ 24,000) are examined. The performance of UF-C-MTVBs, DF-C-MTVBs, UF-D-MTVBs, and DF-D-MTVBs is analyzed and compared with that of the conventional transverse baffles (TBs) and MVBs (e<inf>DR</inf> = 1.0). The experimental setup maintained a constant attack angle (α) of 45°, pitch ratio (p/H) of 1.5, width-shaped ratio (W<inf>b</inf>/W) of 0.25, and blockage ratio (e/H) of 0.3. Tests were conducted at a fixed Prandtl number of 0.71, and a thermochromic liquid crystal sheet was utilized to assess the local Nusselt number distribution on the wall installed with UF-C-MTVBs, DF-C-MTVBs, UF-D-MTVBs, and DF-D-MTVBs. The results reveal that the channel with MVBs (e<inf>DR</inf> = 1.0) achieves the greatest heat transfer rate, with a Nu/Nu<inf>s</inf> ratio of up to 4.37 while a f/f<inf>s</inf> ratio reaching 48.12. In contrast, D-MTVBs at e<inf>DR</inf> = 0.0, despite having a lower Nu/Nu<inf>s</inf> ratio (maximum 3.87), attain the maximum thermal performance of 1.39 at Re = 6000, owing to their optimized design that effectively enhances heat transfer while minimizing pressure drop.
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    Item type:Publication,
    Thermal performance evaluation of a channel with twisted baffles installed: Effect of twisted baffle arrangement
    (2026-03-01)
    Eiamsa-ard, S.
    ;
    Pingta, S.
    ;
    Phila, A.
    ;
    Woncharee, K.
    ;
    Chamoli, S.
    This research aims to introduce newly designed twisted baffle for enhancing heat transfer in solar air heater. This study examined the thermo-hydraulic performance of converging twisted baffles (C-TBs) and diverging twisted baffles (D-TBs) with different numbers of loops (n = 2, 4, 6, and 8) over a Reynolds number range (Re) of 6000–24,000. The results demonstrated that both converging twisted baffles and diverging twisted baffles significantly enhanced heat transfer compared to a smooth channel. The Nusselt number, friction factor, and thermal performance factor (TPF) increased as the number of loops decreased, attributed to stronger flow reattachment. Specifically, twisted baffles with 2, 4, 6, and 8 loops enhanced Nu by approximately 2.29–3.43, 2.02–3.05, 1.77–2.74, and 1.61–2.48 times, respectively, while the friction factor increased by 5.19–5.71, 4.61–5.01, 4.06–4.43, and 3.73–4.06 times, respectively. For a given number of loops, diverging twisted baffles consistently provided higher heat transfer enhancement than converging twisted baffles, albeit with slightly increased friction losses. Across the investigated range, the 2-loop diverging twisted baffles exhibited the best overall performance, achieving the highest Nusselt number ratio (Nu/Nu<inf>SC</inf> where Nu<inf>SC</inf> is the Nusselt number of the smooth channel) of 3.43 and a maximum thermal performance factor of 1.92 at Reynolds number of 6000, establishing it as the optimal configuration among those tested. This research contributes valuable design guidelines for selecting optimal baffle configurations, thereby supporting the development of more energy-efficient solar thermal systems.
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    Item type:Publication,
    Experimental investigation and ANN prediction of heat transfer enhancement in a heat exchanger tube utilizing twin corrugated twisted tapes
    (2025-12-01)
    Du, Y.
    ;
    Wongcharee, K.
    ;
    ; ;
    Chamoli, S.
    This report introduces a novel twin-corrugated twisted tape (TC-TT) insert designed to enhance heat transfer in exchanger tubes. The key innovation lies in the twin-corrugated structure, which generates a twin-swirl flow effect. The corrugated surface synergistically increases flow disturbance and expands the effective heat transfer area. The studied parameters were twist ratios (y/w = 3.0, 3.5, and 4.0) and corrugation angles (θ = 45°, 60°, 75°, and 90°) at 6,000 ≤ Re ≤ 20,000. The results show that using twin-corrugated twisted tapes increases the average Nusselt number by roughly 60–135% compared to a plain tube and by 16–35% compared to a conventional single-twisted tape, confirming the effectiveness of this structural modification. This enhancement is primarily due to the combination of double swirling-flows and enhanced effective heat transfer generated by the corrugated surface. Reducing the corrugation angle (θ) and twist ratio (y/w) led to increases in the Nusselt number (Nu), friction factor (f), and thermal performance factor (TPF). Within the studied range, the Nusselt number, friction factor, and thermal performance factor reached maximum values of 5.18, 0.153, and 1.44, respectively, at a twist ratio of 3.0, a corrugation angle of 45°, and Re = 6,000. Regression analysis was utilized to develop correlations for the Nu and f, considering the Re, Pr, y/w, and θ as influencing variables. The proposed correlations for predicting the friction factor and Nusselt number have errors within ±3% and ±2%, respectively. In addition, an artificial neural network (ANN) was developed for predicting the thermal performance values occurring below the experimental study range. The optimal state ANN model shows remarkable prediction accuracy with R<sup>2</sup> of 0.965.
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    Item type:Publication,
    Investigation of heat transfer enhancement by perforated helical twisted-tapes
    (2014-03-01)
    Nanan, K.
    ;
    ; ;
    Eiamsa-ard, S.
    Influence of perforated helical twisted-tapes (P-HTTs) on the heat transfer, friction loss and thermal performance characteristics under a uniform heat flux condition is reported. The P-HTTs were obtained by perforating typical helical twisted-tapes (HTTs) with a prospect to reduce the friction loss of fluid flow. The experiments were conducted using P-HTTs' three different diameter ratios (d/. w) of 0.2, 0.4 and 0.6, and three different perforation pitch ratios (s/. w) of 1, 1.5 and 2. The helical pitch ratio and twist ratio were fixed at P/. D=2 and y/. w=3. Tests were performed for Reynolds number between 6000 and 20,000. The experiments using the plain tube and the tubes with HTTs were also carried out for assessment. The experimental results reveal that the use of P-HTTs leads to the reduction of friction loss as compare to that of HTT. Heat transfer, friction loss and thermal performance factor increase as d/. w decreases and s/. w increases. For the present range, the maximum thermal performance factor of 1.28 is obtained by using the P-HTT with d/. w=0.2 and s/. w=2.0 at the Reynolds number of 6000. In addition, the empirical correlations for Nusselt number, friction factor and thermal performance factor give accurate predictions within ±. 4%, ±. 6% and ±. 3%, respectively. © 2014 Elsevier Ltd.