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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 R2 of 0.965.
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Intensification of Thermal Performance of a Heat Exchanger Tube with Knitted Wire Coil Turbulators Installed
(2025-12-01)
Wongcharee, K.
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Shoon Wai, T.
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Maruyama, N.
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Hirota, M.
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Chuwattanakul, V.
This study reports on heat transfer augmentation by knitted wire coil turbulators in a fully developed turbulent regime. Four knitted wire coil turbulators with different wire loop number densities (N = 6, 8, 10, and 12 loops per pitch, with 1.0 pitch = 6.8 mm) were tested. Each was made by winding a 0.7 mm copper wire around a 1.0 mm core rod. Experiments were conducted under a constant 600 W/m2 wall heat flux. The flow behaviors observed through a dye injection technique revealed that the wire coil induced secondary flows and developed shear layers, contributing to enhanced heat transfer. Heat transfer improved with increasing wire loop number density. Application of knitted wire coil turbulators increased the Nusselt number (Nu) by 86, 95.4, 103.2, and 109.3% for N = 6, 8, 10, and 12, respectively. This corresponded to increased friction factors (f) by 1.77, 1.97, 2.15, and 2.31 times, respectively. The tube with coils having N = 12 yielded the highest thermal performance index (TPI), 1.4, at a Reynolds number of 5000. The empirical correlations for Nu, f, and TPI showed deviations within ±2.1, ±0.68, and ±2.28%, respectively.
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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.
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Samruaisin, P.
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Kaewkosum, P.
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Pingta, S.
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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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Investigation of turbulent thermal-hydraulic behaviors of a heat exchanger tube with U-cut twisted-tape
(2025-03-01)
Wongcharee, K.
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Chuwattanakul, V.
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Chamoli, S.
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Maruyama, N.
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Hirota, M.
This study examines the influences of U-cut twisted tapes (U-TTs) on thermal-hydraulic behaviors in a circular tube with uniform heat flux. The geometric parameters studied include six U-cut ratios (s/t = 0.5, 1.0, 1.5, 2.0, 2.5, and 3.0) and two twist ratios (y/w = 3.5 and 4.0). Experimental results revealed that their U-cut ratios highly influenced heat transfer enhancement. U-TTs with U-cut ratios (s/t) of 0.5, 1.0, 1.5, and 2.0 achieved higher Nusselt numbers than conventional twisted tapes (TTs). In contrast, U-TTs with larger U-cut ratios (s/t = 2.5 and 3.0) showed reduced Nusselt numbers. However, friction losses with all U-TTs were consistently higher than those with TTs. Due to their excellent heat transfer enhancement, U-TTs with s/t ratios of 0.5 and 1.0 exhibited significantly higher thermal performance factors (TPF) than conventional TTs. The highest TPF, 1.28, was achieved by U-TTs with an s/t ratio of 0.5 and a y/w of 3.5 at a Reynolds number of 6000.
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Parametric study on thermal performance augmentation of TiO2/water nanofluids flowing a tube contained with dual counter twisted-tapes
(2024-07-01)
Thianpong, C.
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Wongcharee, K.
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Kunnarak, K.
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Chokphoemphun, S.
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Chamoli, S.
The study of compound heat transfer enhancement technique using dual counter twisted tapes (DCTs) together with TiO<inf>2</inf>/water nanofluids was carried out. The dual twisted tapes in form of counter-swirl tape arrangement were utilized at three twist ratios (y/w = 1.5, 2.0 and 2.5). TiO<inf>2</inf>/water nanofluids having three different volume concentrations (φ = 0.05, 0.10 and 0.15 %) were employed as the testing fluids. The results indicated that heat transfer rate, friction factor and thermal enhancement index rose with decreasing tape twisted ratio and elevating nanofluid concentration. The TiO<inf>2</inf>/water nanofluids applied in the present work offered higher Nu than pure water (the base fluid) by 7.3–10.0 %. The application of DCT with the smallest y/w of 1.5 and TiO<inf>2</inf>/water nanofluids with the largest φ of 0.15 vol% led to the highest thermal enhancement index (TEI) of 1.53, under the same pumping power criteria. Additionally, the k-nearest neighbor (k-NN) and artificial neural network (ANN) were developed to predict the thermal enhancement index (TEI). It was found that the k-NN and ANN models provided maximum R2 values of 0.919 and 0.992 f, respectively.
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Aerothermal performance evaluation of a tube mounted with broken V-ribbed twisted tape: Effect of forward/backward arrangement
(2023-01-01)
Chuwattanakul, V.
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Wongcharee, K.
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Ketain, P.
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Chamoli, S.
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Thianpong, C.
An experimental investigation on the aerothermal performance of a heat exchanger tube equipped with newly designed broken V-ribbed twisted tapes (B-VRT), was carried out. In the present work, the heat transfer intensification by a B-VRT can be attributed to greater mixing caused by two flow characteristics: 1) longitudinal vortices from the ribs and 2) swirling flow from the twisted tape. The B-VRT with rib attack angles (α) of 45°, 60°, 75°, and 90°, were tested using air as the test fluid. The experimental results of the tube with B-VRTs in a forward/backward arrangement were compared to those of a plain tube alone and a tube with typical twisted tapes (TT) for Reynolds numbers between 6,000 and 20,000. The results indicated that the tube with the B-VRT having forward facing ribs with α = 45° gave the best performance with Nusselt number ratio (Nu/Nup) of 2.27, a friction factor (f/fp) of 4.4, and an aerothermal performance factor (APF) of 1.38. For the range investigated, the B-VRT offered up to 31.9% higher Nusselt numbers than TT. The B-VRT with the smallest rib attack angle (α) of 45° offered higher aerothermal performance factors than the ones with rib attack angles (α) of 60°, 75°, and 90° by approximately 6.85%, 12.99%, and 20.2%, respectively. The results of the B-VRT with optimum geometry (α = 45°) were benchmarked against those reported in similar published papers. Evidently, the aerothermal performance factors the B-VRT were superior to those of most of other tube inserts, especially at low Reynolds numbers. Finally, within the range of parameters (α, y/W and Re) taken into consideration in this study, correlations of Nu and f were developed to estimate the heat transfer and pressure drop. The correlations for Nu, f, and APF showed acceptable prediction accuracies, with respective deviations of ±4%, ±5.4%, and ±4%.
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Effect of conical air distributors on drying of peppercorns in a fluidized bed dryer: Prediction using an artificial neural network
(2022-08-01)
Chuwattanakul, V.
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Wongcharee, K.
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Pimsarn, M.
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Chokphoemphun, S.
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Chamoli, S.
The effect of conical air distributors on the drying of peppercorns in a fluidized bed dryer was experimentally studied. A flat perforated sheet was installed in the column at the base of the bed. Conical air distributors consisted of two parts. The first was a solid cone located below an air duct, while the second part was a perforated metal cone placed on the flat perforated sheet. Experiments were carried out using perforated metal cones with three different height to base diameter ratios, (h/H) values of 0.5, 1.0, and 1.5 and three different air velocities, 1.2Umf, 1.6Umf, and 2.0Umf. An air distributor, consisting of a solid cone and a perforated metal cone with h/H = 1.0 and an air velocity of 2.0Umf, showed the best drying performance. It was also discovered that increasing the air velocity accelerated the drying process. A neural network was created to predict the moisture content of peppercorns during the drying process. The split, sample type, spilt ratio, momentum, and learning rate, as well as the numbers of hidden layers, hidden nodes, and training cycles all had an impact. A maximum coefficient of determination of 0.996 was found for the best model.
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Heat transfer characteristics of a swirling impinging air jet emerging from a triple spiral-corrugated nozzle with a twisted tape installed
(2022-07-01)
Eiamsa-ard, P.
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Wongcharee, K.
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Kunnarak, K.
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Kumar, M.
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Eiamsa-ard, S.
Thermal visualization using a thermochromic liquid crystal sheet was performed to investigate and compare heat transfer behavior of a swirling impinging jet emerging from a triple spiral-corrugated nozzle with a twisted tape (SIJ with TT), a SIJ issuing through a triple spiral-corrugated nozzle, and a typical/conventional impinging jet (CIJ) emerging from a smooth straight circular nozzle. The experimental results showed that the stronger jet recirculation close to the wall due to the swirl flow created by triple spiral-corrugated nozzle and twisted tape inserts (SIJ with TT) support in reducing the value of Nusselt number between the stagnation region and surroundings. For the SIJ with TT, the average Nusselt number performed by the jets with L/d<inf>H</inf> shows that the magnitude of the heat transfer coefficient was significantly enhanced with increasing twist ratios. The maximal value Nu of the SIJ with TT was obtained at the lowest twist ratio (y/W = 2.0). This was up to 5.7 % and 35.5 % higher than those of the SIJ with TT at y/W = 4.0, and the CIJ, 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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Characterization of heat transfer and artificial neural networks prediction on overall performance index of a channel installed with arc-shaped baffle turbulators
(2021-08-01)
Promvonge, P.
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Eiamsa-Ard, S.
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Wongcharee, K.
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Chuwattanakul, V.
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Samruaisin, P.
Influences of baffle pitch ratio (p/w) and attached angle of arc-shaped baffles (AB) on the overall performance index (OPI) of a channel installed with AB have been carefully studied. In addition, an artificial neural network (ANN) model for predicting the OPI of the channel was reported. The arc-shaped baffle (AB) showed a significant effect on the augmented heat transfer and friction loss penalty as compared to a smooth channel. As the attached arc shaped angle (θ) increased, both Nusselt number and friction factor intensified. The Nusselt number values at θ = 90° were higher than those at θ = 20°, 40°, 60°, and 80° by up to 5.8%, 3.9%, 2.3% and 2.5%, respectively. The Nusselt number increased when the p/w was raised from 4.0 to 8.0 while the opposite trend was observed when the p/w was raised from 8.0 to 12.0. The maximum OPI of 1.43 was achieved by using the baffles with θ = 90° and pitch ratio of 8.0 at Re = 4000. For the development of ANN models for predicting the OPI, it was found that the best predictive performance was (R2) of 0.99843407 for ANN model of 3-50-50-1 with Tanh-Tanh activation function at epoch of 1200.

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