Chuwattanakul, Varesa

Preferred name

Alternative Name

Chuwattanakul, V.

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School of Engineering

varesa.ch@kmitl.ac.th

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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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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/m<sup>2</sup> 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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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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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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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 evaluation of turbulent flows through gear-ring elements
(2017-01-01)
Ruengpayungsak, K.
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Wongcharee, K.
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Thianpong, C.
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Pimsarn, M.
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Chuwattanakul, V.
Heat transfer and friction loss characteristics in tubular heat exchangers with gear-ring turbulators (GR-Ts) have been experimentally and numerically investigated. The GR-Ts with different free-space length ratios (SR = s/D = 1.0, 2.0 and 3.0) and tooth numbers (N = 8, 16 and 24), were experimentally tested under constant wall heat flux in turbulent flow (Reynolds numbers from 6000 to 20,000). Air was used as the working fluid. The behaviors in a plain tube and the tube with a conventional ring turbulators (N = 0) were also studied for comparison. The results show that utilizing tubes with GR-Ts leads to the increases of heat transfer coefficient and pressure loss as compared to those associated with the use of a plain tube. Heat transfer enhancement and friction increase with decreasing free-space length ratio (SR) and tooth number (N). Among the investigated inserts, the conventional ring turbulators (N = 0) with free-space length ratio, SR = 1.0 give the highest heat transfer rate and friction factor at 2.7 times and 15.5 times of those of the plain tube. However, the maximum thermal performance factor of 1.3 is obtained by using the GR-Ts with the largest free-space length ratio and maximum tooth number (SR = 3.0 and N = 24). At SR = 3.0, the GR-Ts with tooth numbers (N) of 0, 8, 16 and 24 yield thermal performance factors up to 1.24, 1.26, 1.28 and 1.3, respectively. The numerical results are given for a better understanding of flow and heat transfer characteristics associated with the use of GR-Ts.
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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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Intensification of thermo-hydraulic performance in heat exchanger tube inserted with multiple twisted-tapes
(2018-05-25)
Piriyarungrod, N.
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Kumar, Manoj
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Thianpong, C.
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Pimsarn, M.
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Chuwattanakul, V.
The present work presents the thermo-hydraulic characteristics in the heat exchanger tube inserted with multiple-twisted tapes (M-TT). Multiple-twisted tapes consisted of a larger twisted tape and small twisted tapes which were placed along with the larger twisted tape. The study encompassed 6 different twist ratios of the small twisted tapes (y/w = 2.5, 5, 10, 15, 20 and 25) and 5 different numbers of the small twisted tapes (N = 2, 3, 4, 5 and 6). Experiments were conducted under uniform wall heat flux condition by using air as the testing fluid for Reynolds numbers from 6000 to 20,000. A large single twisted tape in a tight-fit form (T-TT) and that in a loose-fit form (L-TT) were tested as the reference cases for comparison. The experimental results found that the use of multiple-twisted tapes (M-TT) with N = 3, 4, 5 and 6 leads to the considerable increases in heat transfer enhancement and friction factor as compared to those of single twisted tape. For multiple twisted tapes (M-TT), Nusselt number (Nu), friction factor (f) and thermo-hydraulic performance factor (η) increase with increasing number (N) and decreasing twist ratio (y/w) of small twisted tapes. The maximum thermo-hydraulic performance factor of 1.2 is obtained by the use of M-TT with N = 6 and y/w = 2.5. In addition, the numerical work on flow and thermal behaviors was also performed for a better understanding of heat transfer mechanisms.
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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 R<sup>2</sup> value of 0.99317.
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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.

Chuwattanakul, Varesa

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