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Thermal effectiveness and entropy-exergy estimation in a tube with punched double V-winglets
(2026-06-01)
Jayranaiwachira, Nuthvipa
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Sripattanapipat, Somchai
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Promvonge, Pongjet
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Erfanian Nakhchi, Mahdi
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Skullong, Sompol
Vortex generators are effective devices for enhancing heat transfer rates in heating or cooling systems with minimal frictional losses via the production of streamwise vortices. This research effort presents the perforated double V-winglet (P-DVW) and looks at how it affects heat transmission and friction when mounted inside a heat exchange tube that is consistently heated for producing multiple vortices whereas its flow is turbulent. Optimizing thermal performance for increased energy savings and maximizing the Nusselt number ( Nu ) to minimize heat exchanger size are the major goals. Thermal characteristics, including generated entropy and exergy efficiency, are explored in depth. A Reynolds number (Re) that varies from 4760 to 29,270 is employed to explore the friction and thermal features of the tube. The P-DVW parameters encompass attack angles of α<inf>2</inf> = 15° and α<inf>1</inf> = 30°, four porosity ratios ( A <inf>h</inf>/ A <inf>w</inf> = 0, 0.0188, 0.0523, and 0.1026), and three pitch ratios, P<inf>R</inf>, (0.75, 1, and 1.25), while maintaining a constant winglet height. At P<inf>R</inf> = 0.75 and A <inf>h</inf>/ A <inf>w</inf> = 0, the P-DVW exhibits peak f and Nu values around 23.83 and 5.31 times bigger than those of the plain tube, accordingly. Further, under the specified conditions, it yields minimal entropy production, while the optimal exergy efficiency is roughly 0.9829. The thermal effectiveness of P-DVW is anticipated to reach its maximum at 2.55 with Nu<inf>R</inf> = 4.54 at A <inf>h</inf>/ A <inf>w</inf> = 0.0523 and P<inf>R</inf> = 0.75 to reveal its actual benefits. Furthermore, the correlations of f , Nu , and TEF were determined for the examined range of values.
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Augmentation of solar air heater effectiveness with flapped triangular-wings
(2025-12-01)
Promvonge, Pongjet
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Sripattanapipat, Somchai
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Jayranaiwachira, Nuthvipa
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Nakhchi, Mahdi Erfanian
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Skullong, Sompol
An experiment was conducted to identify the optimal method for enhancing the thermal effectiveness of a solar air heater duct utilizing flapped triangular-wing (FTW) vortex generators affixed to the absorber. The wings are structured in two configurations: backward FTW (B-FTW) and forward FTW (F-FTW), each incorporating a louver-flapped opening for lowering frictional loss. This study seeks to improve the Nusselt number ratio (Nu<inf>R</inf>) while lowering friction loss to optimize thermal effectiveness, hence minimizing the overall dimensions of thermal energy systems. The research findings focus on heat transmission (Nu) and frictional loss (f), encompassing thermal effectiveness across the entire range of Reynolds numbers (Re) from 5280 to 22,510. The FTW elements are configured in B-FTW and F-FTW forms, employing three relative pitches (P<inf>R</inf> = 0.75, 1.25, and 1.75) and five flap angles (θ = 0°, 35°, 45°, 65°, and 90°), while maintaining a constant attack angle (α = 45°) and a wing height ratio (B<inf>R</inf> = 1). The research findings demonstrate that the FTWs produce a significant increase in Nu contrasted to the smooth duct, which varies from 4.72 to 8.05 times, while the increase in f is approximately 13 to 68.1 times. For P<inf>R</inf> = 1.25, θ = 45°, and lower Re, the greatest thermal effectiveness factor (TEF) is roughly 2.87 for the F-FTW and 2.64 for the B-FTW, while Nu<inf>R</inf> is approximately 6.98 for the F-FTW and 6.29 for the B-FTW. This implies that the largest TEF is exclusively associated with the F-FTW, and therefore, the B-FTW should be averted in practice. Additionally, correlations are established and documented for the key quantities (Nu, f, and TEF).
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Augmented thermal effectiveness in solar air receiver with flapped curved winglets: Experimental and numerical analysis
(2025-12-01)
Sripattanapipat, Somchai
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Promvonge, Pongjet
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Jayranaiwachira, Nuthvipa
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Promthaisong, Pitak
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Nakhchi, Mahdi Erfanian
Thermal effectiveness was examined on a solar air receiver equipped with a new lengthwise vortex generator, namely a flapped curved winglet (FCW) mounted on the absorber, utilizing experimental and numerical approaches. Two arrays were employed to assemble two FCWs on the absorber at an angle of attack (α = 59.5°). The FCWs' V-tips were orientated upstream (VU-FCW) and downstream (VD-FCW). Air served as the working fluid, entering a constantly heat-fluxed channel at Reynolds numbers (Re) varying from 5280 to 22,510. Three relative winglet pitches (P<inf>R</inf> = P/H = 1.0–2.0), five winglet-mounted flap angles (β = 0° - 90°), and one winglet blockage ratio (b/H=B<inf>R</inf> = 0.6) were among the major factors. According to the findings, lowering P<inf>R</inf> and β greatly enhances the f (friction factor) and Nu (Nusselt number) of the two FCW arrays. The FCW with P<inf>R</inf> = 1.0 and β = 0° has the largest Nu and f values, approximately 8.3 and 77.39 times bigger than the smooth flat channel, as per the test data. The maximal thermal effectiveness factors (TEF) of the VD-FCW and VU-FCW were approximately 2.83 and 2.61, respectively, at comparable β = 45° and P<inf>R</inf> = 1.5. The f and Nu correlations in employing FCW were also provided. A 3D computational analysis employing the realizable k-ε turbulence model was conducted to examine heat transmission and flow patterns, with the corresponding measured data validating the expected results. The numerical and measured data sets yielded consistent results, and the FCW's heat transmission mechanism was also described.
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Thermal effectiveness analysis of heat exchange tube with staggered louver-punched V-baffles
(2024-12-01)
Promvonge, Pongjet
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Jayranaiwachira, Nuthvipa
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Promthaisong, Pitak
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Nakhchi, Mahdi Erfanian
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Skullong, Sompol
An experiment has been conducted to ascertain the optimal approach for enhancing the convective transmission of heat in a heat exchanger tube by periodically positioning staggered louver-punched V-baffle (SLVB) vortex generators on a perforated tape. The louver-punched V-baffles were staggered and set up with two patterns: V-apex directing upstream (VU) and downstream (VD), and each featured a louver-punched aperture to minimize friction loss. The aim of this work was to rise the thermal effectiveness as well as the Nusselt number ratio (Nu<inf>R</inf>) at optimal effectiveness in order to cut down on overall dimension of heat exchangers. Consequently, the research findings focused on behaviors of heat transmission and frictional loss, incorporating generated entropy, through a variety of Reynolds numbers (Re) spanning 29,270 to 4762. The SLVB elements were designed and placed in VU and VD forms using three relative pitches (P<inf>R</inf> = 0.5, 1.0, and 1.5) as well as six louver-flapped angles (θ = 0°, 10°, 20°, 30°, 45°, and 90°), all at the same attack angle (α = 52°), a baffle height ratio (B<inf>R</inf> = 0.3) and a louver size ratio (L<inf>R</inf> = 0.73). As demonstrated by the experiment, the θ = 20° generated the best heat transfer of all P<inf>R</inf> values, up to 6.55 times greater than the smooth tube, despite having a lower friction loss than the θ = 0° (solid baffle). At P<inf>R</inf> = 0.5, θ = 20° and smaller Re, the optimum thermal effectiveness factor (TEF) and Nu<inf>R</inf> values were, respectively, about 2.65 and 6.55 for the VU SLVB and 2.52 and 6.04 for the VD one. It implied that the TEF strategies can be utilized to anticipate the best effectiveness under identical scenarios. Also, correlations for the critical parameters, namely, Nu, f, and TEF, were estimated and documented.
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Effect of trapezoidal louvered winglets on increased heat transfer and exergy in tubular heat exchanger
(2024-10-01)
Promvonge, Pongjet
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Thianpong, Chinaruk
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Jayranaiwachira, Nuthvipa
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Nakhchi, Mahdi Erfanian
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Skullong, Sompol
The effect of inserting a trapezoidal louvered winglet tape (TLWT) into a uniformly heat-fluxed tube on its thermal effectiveness was studied experimentally. The exergy and entropy analyses for turbulent flows, as well as frictional loss and thermal features, were highlighted as key aspects of the experimental finding for the Reynolds number which measured between about 4700 and 30,000. Because fixing baffles to the curved shape of tube wall presented a challenge, the baffles were consequently positioned on double surfaces of a flat tape. Six values of the louver angle (θ<inf>1</inf> = 0°, 25°, 30°, 45°, 60°, and 90°) and three values of the relative pitch of winglet (P<inf>R</inf> = 1.0, 1.5, and 2.0) were employed in the arrangement of TLWTs, with the V-apex oriented upstream (V-up). Each of these had only a fixed height (B<inf>R</inf> = 0.25) and angle of attack (α = 30°). The winglets were utilized to induce streamwise vortices which can hinder the boundary layer formation, while the louvered openings were adopted to lessen pressure drop without significantly impacting the primary vortices. The experiment results disclosed that the smallest θ<inf>1</inf> and P<inf>R</inf> produced the largest relative friction factor (f<inf>R</inf>) and Nu<inf>R</inf>, which were about 13.57 and 4.04 times higher, while P<inf>R</inf> = 1 and θ<inf>1</inf> = 45° provide the greatest TEF of about 2.27. The greatest exergy efficiency (η<inf>Ex</inf>) resulting from the TLWT was reached at θ<inf>1</inf> = 0°, but the generation of entropy (S˙<inf>g</inf><sup>′</sup>) dropped with lowering θ<inf>1</inf> and Re. A further examination, however, showed that the best scenario with α = 60° and staggered arrays is more desirable since it yields the largest TEF of 2.45 at θ<inf>1</inf> = 45° and P<inf>R</inf> = 1. For the range of parameters under consideration, the Nu and f correlations were additionally established.
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Thermal-hydraulic performance of solar receiver duct with inclined punched-ribs and grooves
(2022-11-01)
Jayranaiwachira, Nuthvipa
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Promvonge, Pongjet
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Thianpong, Chinaruk
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Skullong, Sompol
The article presents an experimental study on turbulent airflow friction and thermal behaviors in a solar receiver heat exchanger duct mounted with combined inclined chamfered-groove and turbulators. The experimental work was conducted for Reynolds numbers from 5,300 to 24,000, based on the hydraulic duct diameter. The 45°-inclined punched-ribs and grooves were placed periodically on the absorber plate. The punched-rib parameters were four inclination angles (β = 0°, 45°, 90° and 135°) of the punched holes and three relative rib pitches (PR = 1, 1.5 and 2) whereas only a rib blockage ratio (BR = 0.5) and an angle of attack (α) of 45° were fixed. Similarly, the parameters of the grooves included only three groove-pitch ratios (PR), similar to the rib pitches and one groove blockage ratio (BR = 0.2). The experimental result has revealed that the combination of rib-groove turbulators at β = 0° (solid rib) and PR = 1 gives the maximum heat transfer rate and friction loss while the greatest thermal enhancement factor of 2.1 was found at β = 45°, PR = 1. Moreover, the friction loss and heat transfer correlations for this thermal system were determined.
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Numerical Heat Transfer Investigation in a Heat Exchanger Tube with Hexagonal Conical-ring Inserts
(2016-11-01)
Sripattanapipat, Somchai
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Tamna, Sombat
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Jayranaiwachira, Nuthvipa
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Promvonge, Pongjet
The hexagonal conical rings (HCR) modified from the typical conical ring (CR) are used as a turbulence promoter for producing the vortex flows to enhance the heat transfer rate in a heat exchanger tube. To reduce the pressure loss, the V-shaped HCR (V-HCR) obtained by cutting both symmetric plane of the cone-tip of HCR at 30°, 45°and 60°is offered in the present work. The tube fitted with V-HCR elements having a fixed inlet and outlet diameter is numerically investigated. The computation is carried out for Reynolds number in a range of 3000 to 20,000 in a uniform heat-fluxed test tube. The numerical results show that the V-HCR insert leads to much higher heat transfer than the typical CR/HCR insert or the smooth tube alone and also provides lower friction factor. The 30°V-shaped HCR gives the highest heat transfer and thermal performance due to the lowest friction loss, indicating the promising device of the V-HCR.
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3D numerical study on flow structure and heat transfer in a circular tube with V-baffles
(2015-02-01)
Jedsadaratanachai, Withada
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Jayranaiwachira, Nuthvipa
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Promvonge, Pongjet
A 3D numerical investigation has been carried out to examine periodic laminar flow and heat transfer characteristics in a circular tube with 45° V-baffles with isothermal wall. The computations are based on the finite volume method (FVM), and the SIMPLE algorithm has been implemented. The fluid flow and heat transfer characteristics are presented for Reynolds numbers ranging from 100 to 2000. To generate main longitudinal vortex flows through the tested section, V-baffles with an attack angle of 45° are mounted in tandem and in-line arrangement on the opposite positions of the circular tube. Effects of tube blockage ratio, flow direction on heat transfer and pressure drop in the tube are studied. It is apparent that a pair of longitudinal twisted vortices (P-vortex) created by a V-baffle can induce impingement on a wall of the inter-baffle cavity and lead a drastic increase in heat transfer rate at tube wall. In addition, the larger blockage ratio results in the higher Nusselt number and friction factor values. The computational results show that the optimum thermal enhancement factor is around 3.20 at baffle height of B = 0.20 and B = 0.25 times of the tube diameter for the V-upstream and V-downstream, respectively.
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Thermal behaviors in a square duct with U-ribbed tape inserts
(2014-01-01)
Khanoknaiyakarn, Chitakorn
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Skullong, Sompol
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Promvonge, Pongjet
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Jayranaiwachira, Nuthvipa
This paper presents an experimental study on thermal characteristics in a constant heatfluxed square-duct heat exchanger with U-ribbed tape inserts. The experiments are carried out by varying airflow rate for Reynolds number ranging from 4000 to 38,000. The insertion of the Uribbed tape is performed with an axial rib-pitch set to four times duct-height (4H) at a single attack angle, α=45° and the ribbed tape is diagonally inserted in the square duct in order to generate longitudinal vortex flows. Effects of five blockage ratios (e/H=0.1, 0.15, 0.2, 0.25 and 0.3) on heat transfer and friction loss are experimentally investigated. The experimental result shows that the insertion of the U-ribbed tape at e/H=0.3 provides the highest heat transfer and friction factor values but the one at e/H=0.25 yields the highest thermal performance enhancement. © (2014) Trans Tech Publications, Switzerland.

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