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Thermal performance evaluation of a channel with twisted baffles installed: Effect of twisted baffle arrangement
(2026-03-01)
Eiamsa-ard, S.
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Pingta, S.
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Phila, A.
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Woncharee, K.
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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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Experimental investigation and ANN prediction of heat transfer enhancement in a heat exchanger tube utilizing twin corrugated twisted tapes
(2025-12-01)
Du, Y.
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Wongcharee, K.
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Thianpong, C.
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Chuwattanakul, V.
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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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Multi objective optimization of TiO2/water nanofluid flow within a heat exchanger enhanced with loose-fit delta-wing twisted tape inserts
(2022-02-01)
Thianpong, C.
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Wongcharee, K.
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Safikhani, H.
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Chokphoemphun, S.
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Saysroy, A.
A hybrid technique by using TiO<inf>2</inf>/water nanofluid together with loose-fit delta-wing twisted tape (LTT-W) was employed for heat transfer enhancement. Experiments encompassed the TiO<inf>2</inf>-water nanofluids having concentration (φ) of 0.05%–0.15 vol% and the loose-fit delta-wing twisted tapes having two different wing arrangements (co- and counter arrangement) and three loose-fit ratios (c/D) of 0.0, 0.15, and 0.2. Experimental revealed that the system with combined enhancement technique gave considerably higher heat transfer than the one without enhancement technique. This can be attributed to the combined influences of swirling flow and higher thermal conductivity of the working fluid. Heat transfer rate and thermohydraulic performance rose with the decrease of loose-fit ratio and the rise of nanofluid concentration. The maximum thermohydraulic performance (TPF) of 1.36 was obtained at c/D = 0.0 and φ = 0.15%. The Multi-Objective Optimization (MOO) was also performed to study the optimal thermohydraulic performance by using GMDH models and NSGA II algorithms. The Pareto front, which contains very useful information, were extracted for both co and counter arrangements. The Pareto fronts have recognized very accurately, the best boundary of the experimental data with respect to the lowest friction factor and highest Nusselt number.
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Thermal Performance Evaluation of a Channel Installed with Inclined-Baffle Turbulators
(2020-02-01)
Phila, A.
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Eiamsa-ard, S.
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Thianpong, C.
This study shed light on how heat transfer in a rectangular channel can be significantly enhanced by integrating it with inclined baffles. Experiments were performed to investigate the effect of the inclined baffles at different attack angles (θ) of 0° up to 165° in 15° incremental steps. The pitch length (between the consecutive baffles) to baffle height ratio (P/e) and the baffle height to channel height ratio (e/H) remained constant at 10 and 0.15, respectively. Experiments on a channel without baffles and one with typical transverse baffles (θ = 90°) were also conducted for comparison. Temperatures measured by the thermochromic liquid crystal image processing technique were employed for plotting the temperature contours on the heated surface. The Reynolds number associated with turbulent flow varied from 9000 to 24,000 under a constant wall heat flux scenario. The heat transfer and pressure drop were characterized by the Nusselt number (Nu) and friction factor (f), respectively. The results showed a promising ability of the inclined baffles to improve the heat transfer rate in the channel, however, this came at the price of an increased pressure drop in the system. The impact of the attack angle on heat transfer and thermal efficiency showed that a 60° attack angle was superior to other attack angles. The results were comparable to those for a 120° attack angle. Additionally, this attack angle enabled the system to accomplish a zenith thermal enhancement factor (η) of 1.11 at a Reynolds number of 9000.
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Experimental Study of the Effects of Inclusion of Rectangular-Cut Twisted Tapes on Heat Transfer and Pressure Drop in a Round Tube
(2019-12-01)
Ruengpayungsak, K.
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Kumar, Manoj
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Chuwattanakul, V.
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Eiamsa-ard, S.
Twisted tape inserts were used as swirl generators in the flow through a tube for enhancing heat transfer. Twisted tapes have commonly been applied in many thermal applications used in industry. Several modified twisted tapes have been investigated for improving the thermal performance of heat exchangers. The effects in tubes with modified rectangular-cut twisted tape (RC-TT) inserts with various free-spacing ratios (s/w = 2.0, 2.5, 3.0, 3.5 and 4.0) and edge–width ratios (t/W = 0.1, 0.15, 0.2 and 0.25) on heat transfer and pressure losses are reported. The RC-TT used in this work had a fixed thickness of 1.2 mm, width of 60 mm, length of 2000 mm and twist ratio (y/W) of 3.0. Experiments were performed over a range of Reynolds numbers, 10,000 ≤ Re ≤ 20,000, using air as a test fluid. A tube with a classical/typical twisted tape was also tested for comparison. In all cases, the Nusselt number tended to increase with the Reynolds number, while the friction factor and thermal performance showed the opposite trend. For the rectangular-cut twisted tape inserts, the friction factor and Nusselt number decreased, while thermal performance increased with increasing free-spacing ratios (s/w) and edge–width ratios (t/W). Furthermore, the maximum thermal performance was achieved at the lowest free-spacing ratio (s/w), edge–width ratio (t/W) and Reynolds number (Re).
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Heat transfer enhancement by tapered twisted tape inserts
(2015-10-01)
Piriyarungrod, N.
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Eiamsa-ard, S.
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Thianpong, C.
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Pimsarn, M.
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Nanan, K.
The effects of inserted tapered twisted tapes, their taper angle and twist ratio on heat transfer rate, pressure drop and thermal performance factor characteristics have been reported. The experiments were carried out by using the tapered twisted tapes with 4 different taper angles which θ= 0.0° (typical twisted tape), 0.3°, 0.6° and 0.9°. At each taper angle, the tapered twisted tapes were twisted at three different twist ratios (y/W) of 3.5, 4.0 and 4.5. All tapes were tested under turbulent flow regime for Reynolds numbers between 6000 and 20,000. A twist ratio is defined as the ratio of twist length (y) to twisted tape width at the large end (W). The plain tube was also tested for comparison. Heat transfer enhancement and friction loss increased with decreasing taper angle and twist ratio. Thermal performance factor tended to increase with increasing taper angle and decreasing tape twist ratio. For the present range, the tube with the tape with taper angle (θ) of 0.9° and twist ratio (y/W) of 3.5 yielded the maximum thermal performance factor of 1.05 at Reynolds number (Re) of 6000.
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Heat transfer augmentation by helically twisted tapes as swirl and turbulence promoters
(2012-10-01)
Eiamsa-ard, S.
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Yongsiri, K.
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Nanan, K.
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Thianpong, C.
This paper describes heat transfer enhancement attributed to helically twisted tapes (HTTs). Each helically twisted tape was fabricated by twisting a straight tape to form a typical twisted tape then bending the twisted tape into a helical shape. The experiments were performed using HTTs with three twist ratios (y/. W) of 2, 2.5 and 3, three helical pitch ratios (p/. D) of 1, 1.5 and 2 for Reynolds number between 6000 and 20,000. The conventional helical tape (CHT) was also tested for comparison. The obtained results reveal that at similar conditions (y/. W and . p/. D), HTTs give lower Nusselt number and friction but higher thermal performance factor than CHTs. Heat transfer rate and friction factor increase as the tape twist ratio and helical pitch ratio decrease, while the thermal performance shows opposite trend. In the present range, the highest thermal performance factor of 1.29 is achieved by utilizing the tape with the largest twist ratio (y/. W=3) and helical pitch ratio (p/. D=2) at Reynolds number of 6000. © 2012 Elsevier B.V.
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Thermal performance evaluation of heat exchangers fitted with twisted-ring turbulators
(2012-07-01)
Thianpong, C.
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Yongsiri, K.
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Nanan, K.
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Eiamsa-ard, S.
Heat transfer, friction factor and thermal performance characteristics in a tube equipped with twisted-rings (TRs) are experimentally investigated. The experiments were conducted using TRs with three different width ratios (W/D. =. 0.05, 0.1 and 0.15) and three pitch ratios of (p/D. =. 1, 1.5 and 2) for Reynolds numbers ranging from 6000 to 20,000 using air as a test fluid. The typical circular rings (CRs) were also tested for an assessment. The experimental results reveal that most TRs yield lower Nusselt numbers and friction factor than CRs, except at the largest width ratio (W/D. =. 0.15) and the smallest pitch ratio (p/D. =. 1.0). In addition, Nusselt number and friction factor increase as width ratio increases and pitch ratio decreases. However, a maximum thermal performance factor is associated by TRs with the smallest width ratio and pitch ratio. The empirical correlations of the heat transfer (Nu) and friction factor (f) are also included in this paper. © 2012 Elsevier Ltd.
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Turbulent heat transfer enhancement in a heat exchanger using helically corrugated tube
(2011-03-01)
Pethkool, S.
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Eiamsa-ard, S.
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Kwankaomeng, S.
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Promvonge, P.
The augmentation of convective heat transfer in a single-phase turbulent flow by using helically corrugated tubes has been experimentally investigated. Effects of pitch-to-diameter ratio (P/D<inf>H</inf>=0.18, 0.22 and 0.27) and rib-height to diameter ratio (e/D<inf>H</inf>=0.02, 0.04 and 0.06) of helically corrugated tubes on the heat transfer enhancement, isothermal friction and thermal performance factor in a concentric tube heat exchanger are examined. The experiments were conducted over a wide range of turbulent fluid flow of Reynolds number from 5500 to 60,000 by employing water as the test fluid. Experimental results show that the heat transfer and thermal performance of the corrugated tube are considerably increased compared to those of the smooth tube. The mean increase in heat transfer rate is between 123% and 232% at the test range, depending on the rib height/pitch ratios and Reynolds number while the maximum thermal performance is found to be about 2.3 for using the corrugated tube with P/D<inf>H</inf>=0.27 and e/D<inf>H</inf>=0.06 at low Reynolds number. Also, the pressure loss result reveals that the average friction factor of the corrugated tube is in a range between 1.46 and 1.93 times over the smooth tube. In addition, correlations of the Nusselt number, friction factor and thermal performance factor in terms of pitch ratio (P/D<inf>H</inf>), rib-height ratio (e/D<inf>H</inf>), Reynolds number (Re), and Prandtl number (Pr) for the corrugated tube are determined, based on the curve fitting of the experimental data. © 2010 Elsevier Ltd.
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Heat transfer behaviors in a tube with combined conical-ring and twisted-tape insert
(2007-08-01)
Promvonge, P.
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Eiamsa-ard, S.
Heat transfer, friction factor and enhancement efficiency characteristics in a circular tube fitted with conical-ring turbulators and a twisted-tape swirl generator have been investigated experimentally. The heat transfer test section is heated electrically imposing axially and circumferentially constant wall heat flux boundary conditions. In the experiments, two enhancement heat transfer devices are applied. One is the conical-ring used as a turbulator and placed in the tested tube and the other is the twisted-tape swirl generator placed at the core of the conical-ring. Air as the tested fluid is passed both enhancement devices in a Reynolds number range of 6000 to 26,000. Two twisted-tapes of different twist ratios, Y = 3.75, and 7.5, are introduced in each run. The experimental results reveal that the tube fitted with the conical-ring and twisted-tape provides Nusselt number values of around 4 to 10% and enhancement efficiency of 4 to 8% higher than that with the conical-ring alone. A maximum heat transfer rate of 367% and enhancement efficiency of around 1.96 is found for using the conical-ring and the twisted-tape of Y = 3.75. For all the devices used, the enhancement efficiency tends to decrease with the rise of Reynolds number and to be nearly uniform for Reynolds number over 16,000. In addition, correlations for Nusselt number, friction factor and performance evaluation criteria to assess the real benefits in using the turbulator and swirl generator of the enhanced tube are determined. © 2007 Elsevier Ltd. All rights reserved.

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