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Heat transfer mechanism in turbulent channel flow with V-tapered-baffles: Effect of convergence and divergence direction V-baffles
(2026-01-01)
Chokphoemphun, S.
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Phila, A.
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Promthaisong, P.
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Chamoli, S.
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Maruyama, N.
Solar air heaters are equipment that is utilized in a variety of applications including engineering and agriculture. Improving the transfer performance of heat exchangers is necessary to benefit from efficient energy consumption. The purpose of this work is to examine the effect of novel design V-tapered-baffles on the thermal performance of solar air heaters. The experiment was conducted with the expectation of a constant wall heat flux. In turbulent flow, air serves as the testing fluid with a Reynolds number range of 6,000 to 24,000. Two V-tapered-baffle types were employed in the experiment: convergent (C-VB) and divergent (D-VB) direction V-baffles, which were employed with fixed baffle pitch length of 60 mm and four different convergent and divergent edge baffle heights of 0, 3, 6, and 9 mm. The experimental results are compared with traditional V-baffles (T-VB) and the smooth surface channel. The investigation discovered that installing V-baffles provided a better thermal performance factor than traditional V-baffles. The important factor is that the V-baffles can reduce the friction factor by about 11–50 % compared to the traditional V-baffles under the same conditions. The maximum thermal enhancement factor values for the C-VB and D-VB were 2.19 and 2.13, respectively.
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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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Thermohydraulic performance evaluation of a heat exchanger mounted with oval inclined twisted rings
(2025-03-01)
Samruaisin, P.
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Chuwattanakul, V.
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Thapmanee, P.
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Kumar, M.
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Naphon, P.
This research examines the effects of oval inclined twisted rings (I-TRs) on thermal performance characteristics. Heat transfer enhancement, friction factor, and thermal enhancement factor tests were conducted under uniform wall heat flux with Reynolds numbers (Re) varying from 6000 to 20,000. A systematic investigation was carried out to examine the influence of different pitch ratios (p/D) and oval-ring inclination angles (θ) on thermal enhancement factor (TEF). The experimental results reveal that the Nusselt number increases with decreasing pitch ratio (p/D) and inclination angle (θ) of the I-TRs. At p/D = 1.5, the Nusselt numbers are approximately 8.59 % to 18.78 % higher than those for I-TRs with p/D values of 2.0 and 2.5. At the smallest inclination angle, θ = 30°, the Nusselt numbers are approximately higher than those at θ = 45°, 60°, 75°, and 90° by around 1.56 %, 7.21 %, 13.74 %, and 27.14 %, respectively. At a p/D ratio of 1.5 and an inclination angle of θ = 30°, the resulting thermal enhancement factor (TEF) consistently exceeds unity across the entire Reynolds number (Re) range. In contrast, for other geometries and configurations, some TEF values fall below unity at higher Re. Within the studied range, the highest TEF of 1.12 is achieved at θ = 30°, p/D = 1.5, and Re = 6,000. The key finding suggests that the performance of the thermal system is highly dependent on both the configuration and operational conditions.
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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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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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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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Prediction of heat transfer and fluid flow in a cross-corrugated tube using numerical methods, artificial neural networks and genetic algorithms
(2022-03-01)
Eiamsa-ard, S.
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Chuwattanakul, V.
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Safikhani, H.
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Promthaisong, P.
In this paper, multi-objective optimization of geometric parameters of spirally-cross-corrugated (SCC) tubes is carried out using numerical methods, genetic algorithms (GAs), and artificial neural networks (ANNs). First, the turbulent flow is numerically characterized in various SCC tube geometries using a finite volume method with the realizable k−ε turbulence model. In this approach, the heat transfer coefficient and friction factor f in tubes are calculated. First, two parameters (corrugation pitch-to-diameter ratio (PR = p/D) and corrugation depth-to-diameter ratio (DR = e/D)) are examined in a turbulent flow regime that affects the strength of quadruple longitudinal vortex flows and thermal characteristics. At the final step, using the obtained polynomials for neural networks, multi-objective genetic algorithms (NSGA II) are employed for Pareto based multi-objective optimization of flow parameters in such tubes. This analysis considers two conflicting parameters, f Re and Nusselt number Nu with respect to three design variables, Reynolds number Re, values of PR and DR. Some interesting and important relationships between the parameters and variables mentioned above emerge as useful optimal design principles involved in the heat transfer of such tubes through Pareto based multi-objective optimization. Such important optimal principles would not have been obtained without the use of a combination of numerical techniques, ANN modeling, and the Pareto optimization.
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Influence of a double vortex chamber on temperature reduction in a counter-flow vortex tube
(2021-12-01)
Samruaisin, P.
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Chuwattanakul, V.
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Pimsarn, M.
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Promthaisong, P.
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Saysroy, A.
This article reports the effect of double vortex-chambers with multiple inlet snail entries of N = 1, 4 and 6 nozzles on the energy separation referred to cold gas exit temperature difference (ΔT<inf>c</inf>) in a counter-flow vortex tube type. The experimental work focused on ascertaining the effects of entry air pressure (P<inf>i</inf> = 2, 3 and 4 bar), distance ratios between the two vortex-chamber to the vortex tube diameter (l/D = 0.875–1.125) and the cold gas mass ratio (μ<inf>c</inf>) in a vortex tube. It was found that cold gas exit temperature difference (ΔT<inf>c</inf>) increased with increasing inlet air pressure (P<inf>i</inf>) and number of inlet nozzles (N), and decreasing l/D. Among the studied conditions, the double vortex-chamber operated at the highest P<inf>i</inf> of 4 bar, N = 6, the smallest l/D = 0.875 and μ<inf>c</inf> = 0.38 gave the highest cold gas exit temperature difference (ΔT<inf>c</inf>) of 31.5 °C. In addition, the deep learning optimization technique was also developed to predict the temperatures for different combination of parameters used in this study. It was found that the optimal models provide maximum R2 value of 0.99317.

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