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Effect of louver-perforated V-type baffles on thermal effectiveness and entropy in round tube
(2025-08-01)
Promvonge, Pongjet
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Sripattanapipat, Somchai
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Suchatawat, Maturose
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Nakhchi, Mahdi Erfanian
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Skullong, Sompol
An experimental investigation was conducted to assess the influence of insertion of a louver-perforated V-type baffle (LVB) vortex generator into a consistent heat-fluxed tube on thermal performance. This study aimed to optimize thermal effectiveness to boost energy savings and reduce the heat exchanger size. The experiments focused on investigating the thermal features, as well as estimating the entropy of turbulent flow at Reynolds numbers (Re) varying between 4750 and 29,290. The LVBs were positioned in two different arrays on a supporting tape during the present experiment: “V-down” and “V-up,” with the V-apex oriented upstream and downstream, respectively, at a fixed attack angle (α = 52°). At one relative baffle height (B<inf>R</inf> = 0.3) and pitch (P<inf>R</inf> = 1.0), the LVBs dealt with six louver flapped angles (θ = 0°, 10°, 20°, 30°, 45°, and 90°) in addition to three louver-hole sizes and locations (θ<inf>1</inf>, θ<inf>2</inf> and θ<inf>12</inf>). Comparative analysis was also conducted on data obtained from the current smooth tube. According to the findings, the louver angle θ<inf>1</inf> = 20°, located on the baffle's trailing end, had the greatest relative Nusselt number (Nu<inf>R</inf>), which was 5.9 times for V-down and 6.38 times for V-up. Furthermore, compared to the V-down and V-up solid baffles (θ = 0°), their friction losses were lessened. The V-up LVB reached its minimum value at θ<inf>1</inf> = 20°, corresponding to the lowest Re. At θ<inf>1</inf> = 20°, the V-up LVB attained its minimum entropy generation (S˙<inf>gen</inf>′) and maximum reduced entropy factor (S<inf>R</inf>) around 20.3. At a comparable θ<inf>1</inf> = 20°, the maximal thermal effectiveness factor (TEF) of V-down and V-up were approximately 2.39 and 2.59, respectively. The estimation and documentation of correlations were also performed for the parameters under consideration, namely Nu, f, and TEF.
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Thermal performance augmentation in a solar air heater with twisted multiple V–baffles
(2024-11-01)
Chompookham, Teerapat
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Eiamsa-ard, Smith
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Buanak, Kalong
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Promvonge, Pongjet
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Maruyama, Naoki
A 3D numerical investigation of thermal performance augmentation of a twisted multiple V–baffles in a solar air heater is presented. Two important functions of the twisted multiple V–baffles are to generate multiple impinging flows upon the wall to improve the convective heat transfer (compared with a smooth channel) and reduce the pressure drop (compared with a typical multiple V–baffles). These outcomes enhance thermal performance. The results of heat transfer (in terms of a Nusselt number ratio), pressure drop (in terms of a friction factor ratio) and thermal performance (in terms of a thermal enhancement factor) of a twisted multiple V–baffles were compared with both a smooth channel and a typical multiple V–baffles. Eighty–one cases including those with a pitch ratio of PR = 0.4–2.0; blockage ratio, BR = 0.10–0.20; angle of attack, α = 30o – 60o and a fixed number of twisted loops, n = 2, were investigated in turbulent flow. The results revealed that the twisted multiple V–baffles created multiple impinging jets at the heated wall and help accelerate heat transfer between the wall and the fluid. Compared to a typical multiple V–baffles, the friction factor showed a large decrease while the Nusselt number was slightly lower leading to better thermal performance. Over the study range, PR = 0.4, BR = 0.20, and α = 60o appeared to yield the highest thermal enhancement factor, 2.81 at Re = 3000.
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Numerical heat transfer study of square duct equipped with novel flapped V-baffles
(2024-03-01)
Thianpong, Chinaruk
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Promvonge, Pongjet
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Skullong, Sompol
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Promthaisong, Pitak
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Nakhchi, Mahdi Erfanian
The paper describes a computational study of heat transfer enhancement inside a square duct with V-shaped flapped baffles located repeatedly on the bottom and top walls for fluid flowing with Reynolds numbers (Re) from 3000 to 21,000. The basic goal of this work is to attain the largest relative Nusselt number (Nu/Nu<inf>0</inf>) whilst maintaining the highest thermal performance to improve energy savings. A finite volume method was used in the computations, along with the Realizable k‒ε turbulent model. The variable baffle parameters considered first in the current simulation were the relative height/blockade ratio (B<inf>R</inf> = 0.05−0.2) and the flap angle of the baffle hole (β = 0° − 90°), while the fixed parameters included the attack angle (α = 60°), hole diameter ratio (d<inf>R</inf> = 0.5), and pitch ratio (P<inf>R</inf> = 0.5). To accomplish this goal, the previously mentioned parameters providing the best thermal performance were investigated further by extending the values of B<inf>R</inf> to 0.25−0.3, d<inf>R</inf> to 0.8 and α to 45°−30°. The simulation results indicate that the jet flowing from the flapped hole, as well as the vortices created by the baffle, can boost heat transfer and friction loss in comparison to the plain duct. In comparison, using a flapped baffle with β > 0° results in less friction loss, a greater thermal enhancement factor (TEF), and a higher Nusselt number than using a baffle with no flap. The first investigation disclosed that for B<inf>R</inf> = 0.2 and β = 20°, the greatest TEF of 2.19 with Nu/Nu<inf>0</inf> of 7.9 times are obtained. The extended study, on the other hand, showed that the highest TEF of roughly 2.49 with Nu/Nu<inf>0</inf> of 8.4 times are seen for α = 45°, d<inf>R</inf> = 0.8, B<inf>R</inf> = 0.25 and β = 20° at lowest Re. Thus, the flapped baffle provides a significant increase in Nu/Nu<inf>0</inf> and TEF over the baffle alone.
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Turbulent flow and heat transfer behaviors in a circular tube fitted with multiple V–baffles
(2023-04-12)
Chompookham, Teerapat
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Promvonge, Pongjet
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Skullong, Sompol
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Siriwan, Narin
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Bubphachot, Bopit
This article presents turbulent flow patterns and thermal behaviors in a circular tube mounted with 30° multiple V–baffles. The influences of V–baffle numbers (N) of 2, 3 and 4 with pitch ratios (PR) of 1.0, 1.5 and 2.0 for Reynolds number (Re) between 3000 and 20,000 were investigated numerically at a fixed blockage ratio, BR = 0.05. These simulated results were proposed in four sections: numerical validations, flow and thermal characteristics and thermal performance. It was visible that the multiple V–baffles can help induce the impinging jet leading to disrupting the boundary layer, increasing the fluid mixing, and then enhancing the heat transfer above the plain tube alone. The rises of the number of V–baffles and the lower baffle pitch length led to raising the heat transfer and friction loss. The maximum thermal performance was obtained around 2.06 at N = 4, PR = 1.0 and lower Re.
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Thermal performance augmentation in round tube with louvered V-winglet vortex generator
(2022-01-01)
Promvonge, Pongjet
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Promthaisong, Pitak
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Skullong, Sompol
The article is concerned with investigating the effect of insertion of louvered V-winglet (LVW) vortex generators on convection heat transfer and pressure loss in a tubular heat exchanger. A metal tape was adopted for supporting the 30° LVW elements placed periodically on the edges of the tape to create two pairs of streamwise counter-rotation vortex flows throughout the tested tube. The use of LVWs could help to promote the fast mixing of fluid flow, to break up the development of boundary layer and to induce the impinging jets resulting in the faster heat transfer rate. Air as a working fluid flowed into the tested tube at Reynolds number from about 4200–25,800. The purpose of employing the louver mounted on the winglet is to reduce the pressure loss with slightly deteriorating the strength of main vortices appearing behind the winglet. The winglet parameters were three different relative winglet pitches, (R<inf>P</inf>=0.5–1.5), six louver angles (θ = 10°–90°), at a fixed relative height (R<inf>B</inf>=0.2) and attack angle (α = 30°). Influences of the mentioned parameters on the friction factor and Nusselt number including the thermal performance were explored. The experimental result has shown that among the LVWs the case of R<inf>P</inf> = 0.5, θ = 10° provides the largest friction factor and Nusselt number owing to impingement flows induced from the vortices onto the heated wall in the rear region of the winglet. The investigation reveals that the highest thermo-hydraulic performance from the LVW is about 2.48 at R<inf>P</inf> = 1 and θ = 30°. To scrutinize the flow pattern and the mechanism of enhancing convection coefficient, a 3-dimensional simulation of turbulent tube flow through LVWs was performed and the simulated results were verified with available measurements. The empirical correlations for measured Nu and f data of the LVW were also offered.
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Heat transfer in solar air duct with multi-V-ribbed absorber and grooved back-plate
(2021-04-01)
Promvonge, Pongjet
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Khanoknaiyakarn, Chitakorn
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Sripattanapipat, Somchai
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Skullong, Sompol
The article presents an experimental study on heat transfer and friction behaviors in a solar air duct fitted with multiple V-shaped ribs on the absorber and delta-grooves on the back plate. Measurements were carried out in the test duct having a cross-section of width, W = 300 mm and height, H = 27 mm. The air flow rate inside the duct was varied to have Reynolds numbers based on the duct hydraulic diameter from about 7000 to 30,000. Two vortex flow devices: rib and groove turbulators, were introduced to generate the vortex flows along the duct. In the test duct, the upper/absorber plate having a constant heat-flux was mounted repeatedly by multiple V-shaped thin ribs with an attack angle (α) of 45° relative to main flow direction while the lower/back plate was grooved periodically in the delta/triangular shape with an attack angle (θ) of 60°. In the present investigation, the geometrical parameters of the ribs included three different rib- to duct-height ratios (e/H = B<inf>R</inf> = 0.108, 0.162 and 0.217) and three rib-pitch to duct-height ratio (P/H = P<inf>R</inf> = 1.0, 1.5 and 2.0). The experimental results have shown that the duct with the V-ribbed absorber at B<inf>R</inf> = 0.217, P<inf>R</inf> = 1 in conjunction with the delta-grooved back plate has the greatest heat transfer and pressure loss. However, the use of the combined devices with P<inf>R</inf> = 1, B<inf>R</inf> = 0.108 leads to the highest thermal performance and also provides greater heat transfer and thermal performance than employing the V-rib or the delta-groove alone.
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Experimental and numerical heat transfer study of turbulent tube flow through discrete V-winglets
(2020-04-01)
Promvonge, Pongjet
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Promthaisong, Pitak
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Skullong, Sompol
The article presents an experimental and numerical investigation on heat transfer augmentation in a tubular heat exchanger inserted with discrete-V-winglet (DW) tape. Air entered the DW-inserted tube having a uniform wall heat flux in a turbulent flow regime, Reynolds number from 4200 to 25,800. Two arrangements of DWs: V-tip pointing upstream (V-up) and downstream (V-down) were introduced with three relative winglet heights (R<inf>B</inf>=b/D = 0.1, 0.15 and 0.2) and four relative winglet-pitches (R<inf>P</inf>=P/D = 0.5, 1.0, 1.5 and 2.0), all at a single angle of attack, α = 30°. Effects of those parameters on the heat transfer/Nusselt number (Nu) and friction factor (f) were examined. Also, a novel thermal-performance enhancement factor (TEF) was put forward. The experimental result has shown that at a given R<inf>B</inf>, the smallest pitch length (R<inf>P</inf>=0.5) yields the highest f and Nu. The DW with R<inf>B</inf>=0.2 and R<inf>P</inf>=0.5 has the maximum Nu and f of about 3.8 times and 18.8 times, respectively whereas the one with R<inf>B</inf>=0.15 and R<inf>P</inf>=1.0 gives the highest TEF of about 1.99 and 2.02 for the V-up and V-down, respectively. Moreover, the DW provides higher TEF than the typical V-winglet as expected. To explore the mechanism of heat transfer, a numerical model of the inserted-tube flow was carried out and the numerical result was validated and found in favorable agreement with available measurement. Flow structures and heat transfer patterns from the simulation such as temperature contours and streamlines including the Nusselt number contours were also proposed.
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Heat transfer augmentation in solar receiver heat exchanger with hole-punched wings
(2019-06-05)
Promvonge, Pongjet
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Skullong, Sompol
Thermal characteristics in a solar air heater duct with perforated/punched rectangular wing (P-RW) mounted on the absorber plate have been experimentally examined. Air as the test fluid flowed through the test duct having a constant wall heat-flux with Reynolds number (Re) based on the hydraulic duct diameter from 5300 to 22,600. Two parts on the P-RWs are offered herein. First, the characteristics of forward P-RWs in the tests were three porosity ratios (A<inf>h</inf>/A<inf>w</inf> = 0.12, 0.34 and 0.64) and three relative pitches (R<inf>P</inf> = P/H = 1.0, 1.5 and 2.0) at a single attack angle (α = 60°). The study revealed that the optimal thermal performance is found at R<inf>P</inf> = 1.5 and A<inf>h</inf>/A<inf>w</inf> = 0.34. Second, the optimal P-RWs in the first part was further studied by varying the attack angles, α = 30° 45° and 60° and by rearranging the P-RWs from the forward to the backward P-RWs. The results of the heat transfer rate and flow resistance inside the duct were displayed in terms of Nusselt number (Nu) and friction factor (f), respectively. The experimental results have showed that the P-RWs give the considerable increase in Nu over the flat-plate duct (smooth absorber plate) around 3.91–5.52 times while the increase in f is about 10.37–36.35 times. The highest thermal performance around 2.01 using the backward P-RWs is seen at A<inf>h</inf>/A<inf>w</inf> = 0.34, R<inf>P</inf> = 1.5 and α = 45°. Correlations for Nu and f have also been determined as a function of P-RW parameters.
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Heat transfer in square duct fitted diagonally with angle-finned tape-Part 2: Numerical study
(2012-05-01)
Promvonge, Pongjet
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Skullong, Sompol
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Kwankaomeng, Sutapat
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Thiangpong, Chinaruk
A numerical work has been conducted to examine turbulent flow and heat transfer characteristics in a three-dimensional isothermal-fluxed square-duct fitted diagonally with 30°-angle finned tapes. The computations are based on the finite volume method with the SIMPLE algorithm implemented. The air flow and heat transfer characteristics in the duct are presented for Reynolds number (Re) in a range of 4000 to 20,000. In the current study, a straight tape with 30°-angled fins mounted repeatedly on both sides is inserted diagonally into the test duct to generate a pair of longitudinal counter-vortices in assisting chaotic flow mixing in the duct including vortex-induced impingement (VI) effect. Effects of fin blockage ratio (BR= b/. H) and pitch ratio (PR= L/. H) on heat transfer and pressure drop behaviors in the duct are investigated and the results of the finned tape insert are compared with available measurements. The computation reveals that predicted results from the finned tape insert are in good agreement with measured data. The study indicates that the vortex flow can help to induce impingement/reattachment flows (VI effect) on the duct walls leading to drastic increase in the heat transfer rate over the duct. The rise of the BR and the reduction of the PR results in the increase in Nusselt number and friction factor values. The maximum thermal performance is found to be 1.95 for using the finned tape at BR= 0.2 and PR= 1 whereas the Nusselt number ratio is about 4.5 at lower Re. © 2012 Elsevier Ltd.

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