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Heat transfer performance evaluation of a solar air heater duct with multiple tapered V-baffles
(2025-12-01)
Thianpong, C.
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Kaewkosum, P.
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Woncharee, K.
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Keaitnukul, W.
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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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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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Influence of bed height and drying temperature on shrimp drying characteristics using a fluidized-bed dryer
(2023-08-01)
Nanan, K.
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Eiamsa-ard, S.
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Chokphoemphun, S.
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Kumar, Manoj
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Pimsarn, M.
The aim of this work was to study shrimp drying in a fluidized-bed dryer to develop a process that performs better than traditional (sun dried) shrimp production. In these experiments, the influence of shrimp size (small, medium and large), bed height (h/D = 0.33, 0.66 and 1.0) and air temperature (60, 70 and 80 °C) on the drying rate were studied under a constant blower power. The experimental results showed that the moisture content of boiled shrimp decreased with an increased drying temperature due to the consequently higher temperature differential between the hot air and the shrimp. When the bed height (h/D) was reduced, shrimp moisture removal increased, but it also increased when shrimp size decreased. Moreover, the production rate of dried shrimp under a bed height h/D = 1.0 and drying temperature of 80 °C yielded the highest dried shrimp production rate of 4.83, 4.21 and 3.72 kg/h for small, medium and large shrimps, respectively.
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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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Visualization of heat transfer characteristics using thermochromic liquid crystal temperature measurements in channels with inclined and transverse twisted-baffles
(2020-07-01)
Eiamsa-ard, S.
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Chuwattanakul, V.
Channels with ribs/baffles are widely applied in thermal engineering applications such as heat exchangers, solar water/air heaters and gas turbine cooling. In the present work, inclined and transverse twisted-baffles (I-TBs/T-TBs) are developed for heat transfer enhancement in a channel. The effects of Reynolds number (Re = 4000, 8000, 12,000, 16,000 and 20,000) roughness pitch ratios (p/w = 4.0, 6.0, 8.0, 10.0 and 12.0) and baffle twist ratios (y/w = 2.0, 3.0, 4.0 and 5.0 corresponding to twisted-baffle loop numbers (N) of 5, 7, 8 and 9) were investigated using air (Prandtl number, Pr = 0.7) as a working fluid. Heat transfer behavior was examined using thermochromic liquid crystal temperature measurements. Typical transverse and inclined baffles were also tested for comparison. Heat transfer, flow friction and thermal performance are reported in terms of Nusselt numbers (Nu), Nusselt number ratios (Nu/Nu<inf>s</inf>), friction factors (f), friction factor ratios (f/f<inf>s</inf>) and thermal performance indices (η). Experimental results reveal that under most conditions examined, I-TBs show better heat transfer, lower frictional losses and higher thermal performance than TBs, IBs and T-TBs. For I-TBs, maximum heat transfer and thermal performance are obtained at a moderate pitch ratio (p/w = 6.0). However, in cases of T-TBs, heat transfer and thermal performance monotonically increase with a decreasing pitch ratio. Friction losses caused by both I-TBs and T-TBs decrease considerably with increasing pitch ratio. For I-TBs, heat transfer and thermal performance monotonically increase with increasing twist ratios. However, for T-TBs, maximum heat transfer and thermal performance are obtained at y/w = 3.0. Over the present studied range, a channel with I-TBs having optimal geometry (p/w = 6.0 and y/w = 5.0) yields maximum thermal performance indices, as high as 1.98, which is greater than the maximum values yielded by channels with T-TBs, TBs, IBs, and smooth channels, by around 74.1%, 98%, 52.5% and 98.3%.
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Silver–water nanofluid flow and convective heat transfer in a microfin tube equipped with loose-fit twisted tapes
(2020-06-01)
Samruaisin, P.
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Wongcharee, K.
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Chuwattanakul, V.
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Eiamsa-ard, S.
Heat transfer enhancement and performance of compact heat exchangers have been extensively studied in the past century for the purpose of promoting energy efficiency. Microfin tubes in single/two/multiple-phase flow heat exchangers into which twisted tape swirl generators are installed can promote heat transfer with a moderate pressure loss penalty. This article reports on the enhanced heat transfer of silver–water nanofluids in a microfin tube into which loose-fit twisted tapes are installed in a counter-flow arrangement. The experiments were carried out using nanofluids with various silver concentrations (0.007–0.03 vol%), loose-fit twisted tapes with clearance ratios (c/D) of 0.0 (tight-fit), 0.05, 0.075 and 0.1, for a twist ratio, y/W, of 2.0. The results indicate that the heat transfer rate (Nu) and pressure drop (f) increase with a decrease in clearance ratio (c/D) and increase in silver (Ag) nanoparticle concentration. Additionally, the thermal performance factor tends to increase with the decrease in Reynolds numbers.
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Effect of sparsely placed twisted tapes installed with multiple-transverse twisted-baffles on heat transfer enhancement
(2020-05-01)
Samruaisin, P.
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Kunnarak, K.
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Chuwattanakul, V.
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Eiamsa-ard, S.
The influences of sparsely placed twisted tapes installed with multiple-transverse twisted-baffles on heat transfer and thermal enhancement factor characteristics of tubes were experimentally studied. The tests were performed using sparsely placed twisted tapes with a twist ratio (y/W) of 3.0, a tape width (W) of 60 mm and a space width-to-tape width ratio (S/W) of 0.8. Each twisted tape was installed with multiple-transverse twisted-baffles. The study encompassed multiple-transverse twisted-baffles with four twist ratios (s/w) of 2.0, 2.5, 3.0 and 3.5 and five width ratios (w/W) of 0.10, 0.13, 0.16, 0.19 and 0.22. A typical twisted tape was also tested for assessment. The results showed that twisted tapes installed with transverse twisted-baffles gave higher heat transfer rates, friction factors and thermal enhancement factors (η) than a typical twisted tape. This is attributed to the combined actions of swirl flow caused by the twisted tape inserts and an additional flow disturbance caused by the multiple-transverse twisted-baffles. For the tube with compound devices, the heat transfer rate, friction loss and thermal enhancement factor increased with increasing s/w and w/W of multiple-transverse twisted-baffles. The tube with sparsely placed twisted tapes installed with multiple-transverse twisted-baffles yielded the highest thermal enhancement factor of 1.32.
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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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Effects of spiral start number and depth ratio of corrugated tube on flow and heat transfer characteristics in turbulent flow region
(2019-08-01)
Kongkaitpaiboon, V.
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Promthaisong, P.
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Chuwattanakul, V.
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Wongcharee, K.
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Eiamsa-ard, S.
Influence of spirally-corrugated tubes on heat transfer (Nu), pressure loss (f) and thermal enhancement factor (TEF) characteristics was numerically investigated. The physical models of spirally-corrugated tubes and also a straight circular tube were built for the comparative study. The predictions were performed for the spirally-corrugated tubes with spiral start numbers (N) of 2, 3, 4 and 5 and depth ratios (DR = e/D) of 0.02, 0.04, 0.06, 0.08, 0.1, 0.12, 0.14 and 0.16 at Reynolds numbers of 5000, 8000, 14000 and 20000. The numerical results show that the spiral corrugated tubes created two types of flow structures: main swirl flows (appear around the core) and secondary swirl flows (appear near tube wall) which facilitate heat transfer between the fluid and the tube walls. The overall heat transfer depends on the competition between two effects: the positive effect of the stronger swirl intensity by increasing start number and the negative effect of the difficulty of fluid transfer into grooves by increasing depth ratio. For the investigated range, the corrugated tubes yield Nusselt numbers and thermal performance factors varying from 0.82 to 2.16 times and 0.66–1.2 times of the straight circular tube, respectively. The highest thermal enhancement factor (TEF) of 1.2 is achieved by using the tube with spiral start number of 4 having moderate depth ratio of 0.08 at Re = 5000.
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Influence of regularly spaced quadruple twisted tape elements on thermal enhancement characteristics
(2018-06-01)
Samruaisin, P.
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Changcharoen, W.
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Thianpong, C.
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Chuwattanakul, V.
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Pimsarn, M.
The present work explores the heat transfer, pressure loss and thermal enhancement factor (TEF) behaviors of a tube fitted with regularly spaced quadruple twisted tape elements (RS-QTTs). The effects of free space ratio and twisted tape arrangement (co, counter and cross arrangements) were investigated in turbulent flow regime. Experiments were carried out using all twisted tapes with constant twist ratio of 2.5 under constant heat flux condition. The results show that RS-QTTs in all arrangements yield lower heat transfer rate and cause lower friction loss than full-length quadruple twisted tapes (QTTs) due to the weaker swirling intensity caused by the decaying of swirling flow. Heat transfer rates given by the RS-QTTs with s/y of 0.5, 1.0, 1.5 and 2.0 are lower than those given by the QTTs by around 6.2%, 8.13%, 10.6% and 12.8%, respectively. For RS-QTTs, heat transfer rate, friction loss and TEF increase with decreasing s/y. Over the range reported, the RS-QTTs in cross-arrangement with s/y = 0.5 gives heat transfer rate up to 6.6% over than that of the QTTs and the maximum TEF of 1.27. Moreover, the flow and thermal behaviors were also numerically studied for a better understanding on heat transfer mechanism.

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