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Evaluation of heat transfer performance of a heat exchanger tube mounted with an I-rib twisted tape and twisted winglets
(2025-12-01)
Qiu, Wenxuan
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Samruaisin, Prachya
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Chuwattanakul, Varesa
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Maruyama, Naoki
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Hirota, Masafumi
This study aims to improve the efficiency of heat exchangers and explore the enhancement mechanism of the thermal performance characteristics of heat exchange tubes by I-rib twisted tapes and twisted winglets (I-RTTW) through experimental research and numerical simulation. The I-RTTW structure consists of a central I-type rib and an edge twisted winglet. The key geometric parameters of the edge twisted winglet include the wing depth ratio (d/W = 0.096, 0.13, 0.16), the wing width ratio (w/W = 0.096, 0.13, 0.16), and a fixed twist angle of 45°. The study uses air as the working fluid to systematically analyze the heat transfer performance of the I-RTTW over a range of Reynolds numbers (Re) of 6,000–20,000. The experimental results reveal that the I-RTTW significantly improves heat transfer through a dual mechanism. First, the edge twisted winglet effectively disrupts the fluid boundary layer by inducing secondary flows. Second, the central I-type rib can promote radial mixing of the fluid. Further in-depth analysis of the experimental data revealed that a greater winglet depth ratio (d/W) increases the longitudinal size of the cutting winglet, thereby disturbing the fluid more deeply and increasing boundary layer disruption. An increased winglet width ratio (w/W) significantly enhances the fluid mixing effect by expanding the lateral coverage, thereby reducing thermal resistance and enhancing heat transfer between the pipe wall and the fluid. In terms of flow resistance characteristics, a greater winglet depth ratio directly leads to an increased longitudinal size of the cutting winglet. This strengthens the disturbance of fluid, resulting in increased boundary layer separation and greater eddy losses. Similarly, an increased winglet width ratio leads to greater lateral flow resistance, so that the fluid needs to overcome a larger shear force and higher collision losses. This leads to an increased friction coefficient (f). In the current study, the heat transfer rate of a pipe equipped with I-RTTWs is about 7 to 26% and 68 to 99% higher than that of a pipe equipped with typical tape (TT) and the plain tube, respectively. The friction coefficient is 1.15–1.37 times and 3.46–4.12 times that of a TT and plain tube, respectively. The comprehensive thermal performance index of the pipe with an I-RTTW is as high as 1.29.
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Thermal performance and exergy analysis in a round tube with louvered trapezoidal winglets
(2023-09-15)
Promvonge, Pongjet
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Eiamsa-ard, Smith
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Skullong, Sompol
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Maruyama, Naoki
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Hirota, Masafumi
An experiment was performed to investigate the influence of inserting a louver-punched trapezoidal-winglet (LPTW) into a uniform heat-fluxed tube in order to create a longitudinal vortex generator. This research aims to maximize both the thermal performance to increase energy savings, and the relative Nusselt number (Nu<inf>R</inf>) at the optimal performance to reduce heat exchanger sizes. Therefore, the experimental result was emphasized on the thermal and pressure loss characteristics including entropy, and exergy analysis of the turbulent tube flow for Reynolds numbers (Re) that extended from 4760 to 29,280. The LPTWs were arranged by letting V-tip direct downstream with three attack angles (α = 30°, 45° and 60°) and five louver angles (θ<inf>1</inf> = 0°, 25°, 30°, 45° and 90°), all at a single relative winglet pitch (P<inf>R</inf> = 1.0) and height (B<inf>R</inf> = 0.25). According to the findings, it revealed that the friction factor (f) and Nusselt number (Nu) of the LPTW at α= 60° and θ<inf>1</inf> = 0° are, respectively, up to 29.1 and 5.5 times above those of the plain tube. With decreasing Re and θ<inf>1</inf>, the entropy generation (S˙′<inf>gen</inf>) was reduced to a lower value and the maximum exergy efficiency (η<inf>Ex</inf>) was obtained for the LPTW at α = 60° and θ<inf>1</inf> = 0° The peak thermal performance around 2.5 together with Nu<inf>R</inf> = 4.68 was found at a= 60°, θ<inf>1</inf> = 45° and the lowest Re. However, the optimal condition at α= 60°, θ<inf>1</inf> = 30° was preferable because it provides the greatest Nu<inf>R</inf> = 5.04 at TEF = 2.47. Additionally, correlations for f and Nu were derived and presented for the range of parameters that were taken into consideration.
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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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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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Enhancement of heat transfer in a tube with regularly-spaced helical tape swirl generators
(2005-01-01)
Eiamsa-ard, Smith
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Promvonge, Pongjet
Influence of helical tapes inserted in a tube on heat transfer enhancement is studied experimentally. A helical tape is inserted in the tube with a view to generating swirl flow that helps to increase the heat transfer rate of the tube. The flow rate of the tube is considered in a range of Reynolds number between 2300 and 8800. The swirling flow devices consisting of: (1) the full-length helical tape with or without a centered-rod, and (2) the regularly-spaced helical tape, are inserted in the inner tube of a concentric tube heat exchanger. Hot air is passed through the inner tube whereas cold water is flowed in the annulus. The experimental data obtained are compared with those obtained from plain tubes of published data. Experimental results confirmed that the use of helical tapes leads to a higher heat transfer rate over the plain tube. The full-length helical tape with rod provides the highest heat transfer rate about 10% better than that without rod but it increased the pressure drop. To overcome this, different free-spacing ratio (s = L <inf>s</inf>/L<inf>h</inf>) of 0.5, 1.0, 1.5, and 2.0 were examined. It was found that the space ratio value should be about unity for Re < 4000. The regularly-spaced helical tape inserts at s = 0.5 yields the highest Nusselt number which is about 50% above the plain tube. © 2004 Elsevier Ltd. All rights reserved.

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