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Heat Transfer Analysis in a Channel Mounted with In-Line Downward-Facing and Staggered Downward-Facing Notched Baffles
(2025-09-01)
Phila, A.
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Keaitnukul, W.
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Kumar, M.
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Pimsarn, M.
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Chokphoemphun, S.
This study presents a comprehensive analysis of heat transfer enhancement, flow resistance, and thermal performance in rectangular channels equipped with three baffle configurations: conventional transverse baffles (TBs), in-line downward-facing notched baffles (IDF-NBs), and staggered downward-facing notched baffles (SDF-NBs). The influence of the pitch-to-baffle height ratio (P/e), ranging from 2.0 to 10, was examined across Reynolds numbers from 6000 to 24,000. Results indicate that a P/e ratio of 6.0 consistently yielded the highest Nusselt numbers across all configurations. While the TB configuration produced significant heat transfer at P/e= 6.0, it experienced a substantial friction penalty, with its best thermal enhancement factor (TEF = 1.168) observed at P/e = 8.0. The IDF-NB configuration achieved optimal performance at P/e = 6.0 with a TEF of 1.257, offering a better balance between heat transfer and flow resistance. The SDF-NB arrangement outperformed all other cases, delivering the highest Nusselt number (Nu = 116.9), TEF (1.362), and improved flow reattachment, primarily due to enhanced mixing from the staggered layout. These findings demonstrate that the staggered notched baffle configuration at P/e = 6.0 offers the most effective thermal performance enhancement among the configurations studied.
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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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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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Performance of a heat exchanger with compound inclined circular-rings and twisted tapes
(2022-09-01)
Pimsarn, M.
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Samruaisin, P.
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Thianpong, C.
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Ruengpayungsak, K.
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Eiamsa-Ard, P.
Optimization was done of the aerothermal performance factor (η) of a tube into which a combination of inclined circular-rings (ICRs) and twisted-tapes (TTs) were installed. The key contribution of this research is determination of the appropriate ICR and TT sizes to produce the best heat exchanger performance. An ICR's purpose is to produce counter-rotating vortices, whereas the TT's role is to create swirl flow within a tube to improve turbulence and transfer cold fluid from the core region to the heated-wall zone. The influence of circular-ring inclination angle (α = 30o, 45o, 60o and 90o), number of twisted tapes (H = 2, 4, and 6) and twist ratios (TR = 1.0, 2.0, and 3.0) on heat transfer and pressure losses were assessed to determine an optimum η condition. The heat transfer and friction factor tend to increase with H values and decreasing TR. The heat transfer of ICRs together with TTs is higher than in a plain tube by up to 128.7% and 155.3%, respectively, while it is better than the transverse circular-ring (α = 90o) and twisted-tape by up to 116.9% and 146.5%, respectively. Furthermore, due to moderate heat transfer and low pressure losses, a maximal η of 1.66 was achieved for α = 30o, H = 2 and TR = 3.0 within the examined range.
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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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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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Thermal performance of heat exchanger tube installed with triple twisted-tapes
(2020-09-01)
Samutpraphut, B.
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Promthaisong, P.
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Wongcharee, K.
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Eiamsa-Ard, S.
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Chuwattanakul, Varesa
A current study deals with the numerical analysis of heat transfer intensification, flow-thermal fields, local heat transfer distribution, friction factor and thermal performance behavior of the heat exchanger tubes installed with triple twisted tapes. Each set of triple twisted tapes consists of three twisted tapes having an identical twist ratio. Twisted tapes of interest have three different twisted ratios (y/w = 1.0, 1.5 and 2.0). Simulation was performed for the turbulent flow with Reynolds numbers (Re) ranging from 5000 to 20,000. Numerical results indicate that the use of triple twisted-tapes leads to heat transfer enhancement. Nusselt number (Nu) and friction factor (f) increase while thermal performance factor () decreases with decreasing twist ratio of triple twisted tapes. The Nusselt numbers of the tubes installed with triple twisted-tapes having twist ratios of 1.0, 1.5 and 2.0 are higher than those of the plain tube by around 3.34-4.45, 2.75-3.65 and 2.56-3.41 times, respectively. Friction factors (f) of the tubes installed triple twisted-tapes with twist ratios of 1.0, 1.5 and 2.0 are increased up to 46.1-49.7, 24.16-26.04 and 15.86-17.09 times, respectively, as compared to those of the plain tube. The maximum thermal performance factors of 1.21, 1.23 and 1.32 are obtained by using triple twisted tapes with y/w = 1.0, 1.5 and 2.0 at the Reynolds number of 5000.
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Intensification of convective heat transfer and heat exchanger performance by the combined influence of a twisted tube and twisted tape
(2019-09-01)
Samruaisin, P.
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Kunlabud, S.
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Kunnarak, K.
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Chuwattanakul, V.
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Eiamsa-Ard, S.
Twisted tubes and twisted tapes are swirl flow generators utilized for increasing thermal performance. The combined effects of twisted tubes and twisted tapes on heat transfer, pressure drop and thermal performance were experimentally investigated. Experiments were performed using a trapezoidal shaped twisted tube and twisted tapes having various twist ratios (y/w=2.0, 3.0, 4.0 and 5.0). Water was used as the test fluid in a turbulent regime (4500<Re<16,000). A simulation of velocity, temperature contours and local Nusselt number plots was also performed to gain information about fluid flow and heat transfer. The results of the combined devices are studied with those of a smooth circular tube and a twisted tube alone, for comparison. The experimental results show that at a given Re, the Nusselt number (Nu), friction factor (f) and thermal performance of a twisted tube mounted with a twisted tape are consistently higher than those of the twisted tube alone and a smooth circular tube. Additionally, the heat transfer, friction loss and thermal performance factor increase with a reduction of the twist ratio (y/w) since the tape with a smaller y/w gives stronger and more consistent swirl flow.
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Hydrodynamics investigation of pepper drying in a swirling fluidized bed dryer with multiple-group twisted tape swirl generators
(2019-03-01)
Chuwattanakul, V.
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Eiamsa-Ard, S.
The present work aims to investigation the behavior of drying peppers in a swirling fluidized bed dryer (S-FBD) fitted with multiple twisted tape swirl generators. A multiple-group twisted tape swirl generator was located at the air inlet at the bottom of the bed. The effects of the superficial air velocity (U∗=U/U <inf>mf</inf> = 1.0, 1.1 and 1.2) on the moisture content (MC), moisture content ratio (MR) and drying rate (DR) were examined. The experimental results showed that the S-FBD can reduce the moisture content of peppers more rapidly than a conventional fluidized bed dryer (FBD). The S-FBD gave a higher DR and decreased drying time compared to that of a FBD. The results also indicated that operation at higher superficial air velocities resulted in a greater DR, especially at the beginning stage of the drying process. For the S-FBD, the reduced of MC, MR and DR at a high superficial air velocity (U∗=U/U <inf>mf</inf> = 1.2) was better than at low superficial air velocities (U∗= 1.0 and 1.1). Furthermore, five different drying models were evaluated to predict the performance of the S-FBD.
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An Impingement Cooling Using Swirling Jets Induced by Helical Rod Swirl Generators
(2018-07-26)
Eiamsa-Ard, S.
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Nuntadusit, C.
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Wongcharee, K.
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Chuwattanakul, V.
The heat transfer performance of swirling impinging jets (SIJs) was investigated and compared with that of the conventional jet (CIJ). The swirling jets were induced by helical rod inserts (HRs) fitted with pipe nozzles. The helical rod inserts with two different rod diameter to nozzle diameter ratios (d/D) of 0.46 and 0.64 were employed for comparison. Jet-to-plate distance to nozzle diameter ratio (L/D) was varied from 1 to 5 while Reynolds number was fixed at 20,000. The temperature and Nusselt number distributions on the impinged plate were measured and evaluated using thermochromic liquid crystal (TLC) sheet and image processing technique. The experimental results showed that the swirling jet (SJ) at d/D=0.64 gave higher average heat transfer rate than the SJ at d/D=0.46 up to 6.41% and the conventional jet (CJ) up to 35.05%. In addition, Nusselt number peak of swirling jets increased as jet-to-plate distance decreased.

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