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Thermal performance evaluation of a diamond-shaped roughened tube
(2025-12-01)
Chokphoemphun, Suriya
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Kamma, Panit
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Promvonge, Pongjet
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Promthaisong, Pitak
Thermal performance evaluation was examined numerically in a diamond-shaped roughened tube, which created recirculation and pair counter-rotation flows, which helped to disrupt the boundary layer, and increased fluid mixing led to improving the rate of heat transfer. The parameters studied, including relative depth ratio, e/D, DR, from 0.02 ≤ DR ≤ 0.14, and relative pitch ratio, p/D, PR, from 0.25 ≤ PR ≤ 1.5, under turbulent flow conditions, 3000 ≤ Re ≤ 20,000. Computed results included heat transfer (Nu/Nu<inf>0</inf>), frictional loss (f/f<inf>0</inf>) and thermal performance (in terms of thermal enhancement factor, TEF). The simulations showed that the velocity and heat transfer became fully developed periodic at around x/D ≈ 6–7.5. The pair counter-rotation flows increased the level of both the flow strength and the mixing of fluid, and disrupted the boundary layer, leading to an increase in heat transfer rate. The Nu/Nu<inf>0</inf>, f/f<inf>0</inf> and TEF were achieved in a range of 1.00–3.34, 1.21–24.00 and 0.69–1.56. The maximum TEF was found at 1.56 for DR = 0.08, PR = 0.50 and Re = 5000.
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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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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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Numerical investigation on turbulent forced convection and heat transfer characteristic in spirally semicircle-grooved tube
(2016-12-01)
Promthaisong, Pitak
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Boonloi, Amnart
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Jedsadaratanachai, Withada
Turbulent forced convection and heat transfer structure in the spirally semicircle-grooved tube heat exchanger are numerically examined. The computational problem is solved by finite volume method (FVM) with the SIMPLE algorithm. The influences of groove depth and helical pitch on heat transfer, pressure loss, and thermal performance are investigated for turbulent regime, Re = 5000–20,000. As a result, the swirling flow is found through the test section due to the groove on the tube wall. The flow structure in the spirally semicircle-grooved tube can separate into two types: main and secondary swirling flows. The main swirling flow is found in all cases, while the secondary swirling flow is detected when DR ≥ 0.06. The swirling flow disturbs the thermal boundary layer on the tube wall that is an important reason for heat transfer augmentation. In range studies, the enhancements on heat transfer and friction loss are around 1.16–1.96 and 1.2–10.8 time above the smooth tube, respectively. The optimum thermal performance is around 1.11, which detected at DR = 0.06, PR =1.4,andRe = 5000. The correlations of the Nusselt number and friction factor for the spirally semicircle-grooved tube with PR =1.4 are produced to help to design the tube heat exchanger.

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