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Thermal performance enhancement of a circular tube fitted with inclined perforated disk inserts
(2026-03-01)
Mehta, Rajesh
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Gupta, Anirudh
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Kumar, Nitin
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Eiamsa-ard, Smith
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Thianpong, Chinaruk
Heat exchangers are crucial devices in industries, and enhancing their thermal performance while controlling pressure losses remains a significant challenge. This paper examines the idea that inclined perforated disk (IPD) inserts can be effectively used to improve heat transfer in circular tubes with constant heat flux conditions at acceptable levels of hydraulic penalties. Turbulent airflow with Reynolds numbers (Re) ranging from 5000 to 21,000 was examined in experiments, and three perforation indices (PI = 0.21, 0.24, and 0.27) were tested to determine the effects of hole density on thermal and hydraulic performance. Evidence showed that the Nusselt number (Nu) had been improved by over 86 % compared to plain tubes, with the thermal enhancement factor (TEF) reaching as high as 1.53 at PI = 0.27 and Re = 5000. Particle swarm optimization (PSO) and neural network modelling multi-objective optimization were used to test the results of the experiment and determine the best operating conditions at PI = 0.21. The paper has demonstrated that inclined perforated disk inserts can form a viable passive method for enhancing the efficiency of heat exchangers, as the swirl and jet flow patterns created by the perforations effectively break the thermal boundary layer, thereby increasing the rate of convective heat transfer.
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Thermodynamic performance analysis of a round tube fitted with gradient quadruple twisted tapes
(2026-03-01)
Samruaisin, Prachya
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Liengsirikul, Sathaporn
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Thianpong, Chinaruk
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Chuwattanakul, Varesa
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Chamoli, Sunil
Air-cooled heat exchangers employing twisted-tape passive inserts exist in many forms; however, designing tapes that are practical to manufacture while enhancing heat transfer without incurring excessive pressure drop remains challenging. This study therefore introduces gradient quadruple twisted tapes (GQTT), which gradually vary the pitch across four tapes to control swirl and mix along the tube. In addition, the turn count changes in steps along the four tapes, which triggers extra turbulence near each change and keeps the flow well mixed downstream. This simple and manufacturable pattern aims to boost heat transfer while keeping the added friction under control. Our objective is to evaluate whether GQTT can improve overall performance while keeping the pressure drop within a practical range, in comparison with a plain tube and a constant-turn tape. A realizable k-ε turbulence model, rigorously validated against benchmark data, was applied to eight GQTT variants and benchmarked against a plain tube and a constant-turn tape for Reynolds numbers (Re) between 5000 and 19,000. Spatial second-order schemes, grid-independence testing, and strict residual criteria ensured solution accuracy. Among the candidates, the descending-opposite-pitch configuration (Ds-OPSD) consistently delivered the highest performance. First-law analysis reveals a peak thermal performance factor (TPF) of 1.42 at Re = 5000, equating to a 42 % gain in overall thermo-hydraulic efficiency over the plain tube, with the Nusselt number (Nu) climbing from 57.5 to 100 across the examined Re window. Second-law metrics corroborate this superiority. At the same Re of peak TPF, the Ds-OPSD cuts exergy destruction from 291.4 to 62 W (≈79 % reduction versus the plain tube and ≈22 % versus the constant-turn tape). Total entropy generation remains minimal and nearly constant (S<inf>total</inf> ≈ 0.206–0.212), while the Bejan number stays high (≈0.999–0.971), indicating that the enhancement is achieved without excessive frictional penalties.
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Influence of perforated twisted tapes with vortex generator wings on heat transfer performance and entropy in a heat exchanger tube
(2026-01-01)
Mehta, Rajesh
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Gupta, Anirudh
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Kumar, Nitin
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Eiamsa-ard, Smith
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Pimsarn, Monsak
This study conducts an investigative exploration of thermal and hydraulic performance regarding hybrid inserts which combine perforated twisted tapes with vortex generator wings mounted inside circular tubes. The insert design makes use of both swirl flow and secondary vortex generation which breaks up the thermal boundary layer and boosts convective heat transfer rates. During this investigation, researchers utilized water as the working fluid at Reynolds number (Re) from 3000 to 21,000 to study the effect of three perforation diameter ratio (d/D) 0.143, 0.19, and 0.238 and respective Vortex generator (VG) edge cut ratio (a/D) 0.143, 0.19, and 0.238. Nusselt number (Nu) reach 182.3 % and thermal enhancement factor (TEF) achieve 1.68 at Re = 15,000 when using the enhanced tube compared to a smooth tube. The industrial application of larger VG openings at standard spacing produced a beneficial relationship between thermal performance and flow resistance when the pressure rise reached 345 %. The analysis of entropy generation showed heat transfer irreversibility gave way to frictional irreversibility when both perforation dimension and Re became larger. System design optimization prerequisites involved trade-offs which met Bejan number (Be) analysis trends. The Random Forest machine learning model combined with ANN and Linear Regression models contributed to thermal parameter prediction (Nu, f, TEF) by delivering a predictive accuracy level with less than 6.6 % deviation. The research leads to vital knowledge needed for developing compact heat exchangers integrating passive enhancement methods.
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Enhanced heat transfer performance in channel with delta-wing perforated V-type baffles
(2023-10-01)
Eiamsa-ard, Smith
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Phila, Arnut
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Thianpong, Chinaruk
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Chuwattanakul, Varesa
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Maruyama, Naoki
The article examines the influence of delta-wing V-type baffles (DW-PVBs) on the average Nusselt number, local Nusselt number distribution, pressure losses, and thermal performance behaviors in a channel. Delta-wing perforated V-type baffles (DW-PVBs) mounted in a regular manner on the bottom of a channel produced two pairs of longitudinal counter-rotating vortices to enhance chaotic fluid mixing and destabilize the boundary layer, hence boosting the heat transfer. The geometric characteristics of the delta-wing V-type baffle (DW-PVBs) located on the bottom of the channel were examined at relative baffle blockage and pitch ratios (BR = h/H = 0.3 and p/H = 1.5), and five delta-wing attack angles, θ = 0o (solid V-shaped baffle), 22.5°, 45°, 67.5°, and 90°. The present DW-PVBs mounted on the channel were designed to mitigate pressure loss due to flow blockage. The experiment was done by permitting air to flow through a channel at Reynolds numbers (Re) ranging from 6000 to 24,000. The present results show that the friction factor using the DW-PVBs decreased considerably with increasing θ values. The experimental results revealed that small θ values yielded greater heat transfer and resistance than large θ values. The DW-PVBs with θ = 22.5° performed better than inserts with other θ values in terms of heat transfer rate. It was also observed that the DW-PVBs with θ = 45° gave the maximum thermal performance factor (TPF), while presenting a 13.64–17.26% lower friction factor than the solid V-shaped baffle. Furthermore, it was also found that the DW-PVBs with θ = 0°, 22.5°, 45°, 67.5°, and 90° gave peak TPF values of up to 1.87, 1.89, 1.91, 1.87, and 1.84 at the lowest Reynolds number, 6000.
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Influence of notched baffles on aerothermal performance behaviors in a channel
(2023-07-01)
Phila, Arnut
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Keaitnukul, Warin
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Eiamsa-ard, Smith
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Naphon, Paisarn
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Maruyama, Naoki
The proper designs of modified heat transfer surfaces or turbulence enhancement inserts for heat transfer augmentation are extremely important for improving overall aerothermal performances relating to the energy-saving capabilities of thermal systems. A major challenge is to control friction loss as little as possible while maintaining reasonable heat transfer enhancement. Transverse baffles with rectangular notches or notched baffles (NBs) were applied for improving aerothermal performance in a channel with a constant aspect ratio of 3.75 while notch height-to-baffle height ratio (a/e) ranged from 0.125 to 0.5. Reynolds number ranged from 6000 to 24,000, in experiments. Heat transfer enhancement, pressure loss, and aerothermal performance in a rectangular channel with notched baffles were examined. Compared to the solid transverse baffle (SB, a/e = 0), the NBs with a/e = 0.125 increased the heat transfer rate while lessening the pressure loss, as shown by the experimental findings. Obviously, Nusselt number, friction factor and aerothermal performance increased as the a/e ratio decreased. The NBs with the smallest notch height-to-baffle height ratio (a/e = 0.125) exhibited the highest aerothermal performance of 1.17, which can be attributed to the efficient heat transfer enhancement by the strong multi-jet impingements and the moderate friction loss penalty resulting from the presence of notches (spaces) on the baffles.
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Heat transfer distribution and flow characteristics in a channel with perforated-baffles
(2022-11-01)
Eiamsa-ard, Smith
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Sripattanapipat, Somchai
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Saysroy, Anucha
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Promvonge, Pongjet
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Maruyama, Naoki
The current paper reports the prediction of heat transfer performance of a channel with a modified perforated-baffle in a square wings (SW-PB) form. Numerical results include flow/temperature field, local heat transfer distribution, and thermal performance of a channel installed with the transverse solid baffle (TB), perforated-baffle (PB), and perforated-baffle with square wings (SW-PB). The simulation results demonstrated that TB brought a large recirculation flow, PB induced small recirculation and SW-PB produced several impinging jets as well as recirculation flows. Heat transfer rates given by PB were lower than those provided by TB and SW-PB by around 6.8% and 7.3%, respectively which were accompanied by lower friction losses by about 11.8% and 3.6%, respectively. Although, SW-PB gave higher heat transfer, the assessment of thermal performance factor (TPF) showed that the benefit from lower friction losses was more important. Under the same pumping power, TPFs assisted by SW-PB were higher than that assisted by PB and TB by 6.0% and 3.3%, respectively. The highest TPF of 1.2 was captured by SW-PB at Re = 9,000.
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Thermohydraulics of TiO 2 /Water Nanofluid in a Round Tube with Twisted Tape Inserts
(2019-03-01)
Eiamsa-ard, Smith
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Kiatkittipong, Kunlanan
The influence of TiO <inf>2</inf> nanoparticles with different volume concentrations in water on heat transfer, friction and thermal performance is explored, and finite volume method is used to clarify the heat transfer in a tube inserted with twisted tape (TT). In the experiment, swirling tubes are generated by TT insert with the twisted ratio (y/w) of 3.0 in the range of Reynolds number between 5400 and 15,200. The mathematical modeling which involves the prediction of flow behaviors in a tube is also conducted. The concentration of nanofluid (ϕ) was varied from 0.07 % to 0.21 % by volume. The results revealed that TiO <inf>2</inf> nanoparticles suspended in water enhanced thermal conductivity, and movement of TiO <inf>2</inf> nanoparticles delivered energy exchange. Although an increase of TiO <inf>2</inf> concentration led to an increase in friction due to small particles suspending in fluid, the heat transfer and thermal performance could enhance significantly. As compared to pure water, the presence of TT with TiO <inf>2</inf> nanoparticles at ϕ = 0.07 %, ϕ = 0.14 % and ϕ = 0.21 % indicated a 0.7 %, 1.7 % and 3.1 % higher thermal performance, respectively. With a higher Reynolds number, the thermal performance would be less pronounced due to high flow friction. From the experimental results, the understanding in relation to the effects of TiO <inf>2</inf> concentration and Reynolds number on Nusselt number (Nu), friction factor (f) and thermal performance factor (η) is presented for a wide range of thermophysics and heat transfer application.
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Heat transfer in turbulent tube flow inserted with loose-fit multi-channel twisted tapes as swirl generators
(2017-11-01)
Kunlabud, Suttisak
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Chuwattanakul, Varesa
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Kongkaitpaiboon, Vichan
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Promthaisong, Pitak
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Eiamsa-ard, Smith
Heat transfer and flow behaviors in three-dimensional circular tubes with loose-fit multiple channel twisted tapes were numerically studied. The investigation was examined for Reynolds numbers (Re) ranging from 5000 to 15,000, by using air as testing fluid. Effects of the multiple channel number (N=2,3, and 4), clearance ratio (CR=0.0, 0.025, 0.05, and 0.075) on heat transfer enhancement and flow friction were examined. The numerical results indicate that the tubes with loose-fit multiple channel twisted tapes perform higher heat transfer rates than the plain tube. The enhanced heat transfer rate is escorted with larger pressure drop. Both heat transfer and pressure drop increase with increasing multiple channel number (N) and decreasing clearance ratio (CR). Heat transfer augmented by the loose-fit multiple channel twisted tape with N=4 is higher than those enhanced by the ones with N=2 and 3 by around 9.5–17.8% and 5.8–7.8%, respectively. In addition, the loose-fit multiple channel twisted tapes with clearance ratio of 0.025, 0.05, and 0.075 give lower heat transfer rates than the one with CR=0.0 by around 8.4%, 17.5%, and 28.8%, respectively.
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Thermal characterization of turbulent tube flows over diamond-shaped elements in tandem
(2010-06-01)
Eiamsa-ard, Smith
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Promvonge, Pongjet
Experiments have been conducted to investigate the heat transfer and friction factor characteristics of the fully developed turbulent airflow through a uniform heat flux tube fitted with diamond-shaped turbulators in tandem arrangements. In the experiments, strong turbulence and recirculation flow is expected by using tandem diamond-shaped turbulators (D-shape turbulator) connected to each other by a small rod and placed inside the test tube. The parameters for this study are consisted of Reynolds number (Re) from 3500 to 16,500, the included cone angle (θ = 15°, 30° and 45°), and the tail length ratio (TR = l<inf>t</inf>/l<inf>h</inf> = 1.0, 1.5 and 2.0) defined as the ratio of the tail length (l<inf>t</inf>) to the head length of turbulator (l<inf>h</inf>). The variation of Nusselt number and friction factor with Reynolds number under the effect of those parameters are determined and presented. The experimental result reveals that the heat transfer rate increases with increasing Reynolds number and the included cone angle (θ) but decreases with the rise of the tail length ratio (TR). This is because of the mixing of the fluid in the boundary layer thereby enhancing the convective heat transfer and increasing pressure loss. For the tube with the turbulator of θ = 45°, the heat transfer enhancement is found to be 67%, 57% and 46% for tail length ratio, TR = 1.0, 1.5 and 2.0, respectively. Correlations of the Nusselt number (Nu) and friction factor (f) are developed for the evaluation of interactive effects of using the turbulators on the heat transfer and pressure loss. The good agreement between the experimental and the correlated results is obtained within 5-7% deviation. In addition, the heat transfer enhancement efficiency determined under constant pumping power is also provided. © 2009 Elsevier Masson SAS. All rights reserved.
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Performance assessment in a heat exchanger tube with alternate clockwise and counter-clockwise twisted-tape inserts
(2010-03-01)
Eiamsa-ard, Smith
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Promvonge, Pongjet
The article presents an experimental study of turbulent heat transfer and flow friction characteristics in a circular tube equipped with two types of twisted tapes: (1) typical twisted tapes and (2) alternate clockwise and counterclockwise twisted tapes (C-CC twisted tapes). Nine different C-CC twisted tapes are tested in the current work; they included the tapes with three twist ratios, y/w = 3.0, 4.0 and 5.0, each with three twist angles, θ = 30o, 60o and 90o. The experiments have been performed over a Reynolds number range of 3000-27,000 under uniform heat flux conditions, using water as working fluid. The obtained results reveal that the C-CC twisted-tapes provide higher heat transfer rate, friction factor and heat transfer enhancement index than the typical twisted-tapes at similar operating conditions. The results also show that the heat transfer rate of the C-CC tapes increases with the decrease of twist ratio and the increase of twist angle values. Depending on Reynolds number, twist ratio and twist angle values, the mean Nusselt numbers in the tube fitted with the C-CC twisted tapes are higher than those with the typical ones and the plain tube around 12.8-41.9% and 27.3-90.5%, respectively. The maximum heat transfer enhancement indexes of the C-CC twisted tapes with θ = 90o for y/w = 3.0, 4.0 and 5.0, are 1.4, 1.34 and 1.3, respectively. In addition, correlations of the Nusselt number and the friction factor for using the C-CC twisted tapes are also determined. Both predicted Nusselt number and friction factor are within ±15% and ±15% deviation compared to the experimental data. © 2009 Elsevier Ltd. All rights reserved.

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