KMITL

Permanent URI for this communityhttps://dspace.kmitl.ac.th/handle/123456789/1

Browse

Search Results

Now showing 1 - 10 of 14

Some of the metrics are blocked by your
consent settings
Thermal performance evaluation of a channel with twisted baffles installed: Effect of twisted baffle arrangement
(2026-03-01)
Eiamsa-ard, S.
;
Pingta, S.
;
Phila, A.
;
Woncharee, K.
;
Chamoli, S.
This research aims to introduce newly designed twisted baffle for enhancing heat transfer in solar air heater. This study examined the thermo-hydraulic performance of converging twisted baffles (C-TBs) and diverging twisted baffles (D-TBs) with different numbers of loops (n = 2, 4, 6, and 8) over a Reynolds number range (Re) of 6000–24,000. The results demonstrated that both converging twisted baffles and diverging twisted baffles significantly enhanced heat transfer compared to a smooth channel. The Nusselt number, friction factor, and thermal performance factor (TPF) increased as the number of loops decreased, attributed to stronger flow reattachment. Specifically, twisted baffles with 2, 4, 6, and 8 loops enhanced Nu by approximately 2.29–3.43, 2.02–3.05, 1.77–2.74, and 1.61–2.48 times, respectively, while the friction factor increased by 5.19–5.71, 4.61–5.01, 4.06–4.43, and 3.73–4.06 times, respectively. For a given number of loops, diverging twisted baffles consistently provided higher heat transfer enhancement than converging twisted baffles, albeit with slightly increased friction losses. Across the investigated range, the 2-loop diverging twisted baffles exhibited the best overall performance, achieving the highest Nusselt number ratio (Nu/Nu<inf>SC</inf> where Nu<inf>SC</inf> is the Nusselt number of the smooth channel) of 3.43 and a maximum thermal performance factor of 1.92 at Reynolds number of 6000, establishing it as the optimal configuration among those tested. This research contributes valuable design guidelines for selecting optimal baffle configurations, thereby supporting the development of more energy-efficient solar thermal systems.
Some of the metrics are blocked by your
consent settings
Performance Assessment of Solar Air Heater Channel with Inclined Groove Turbulators
(2025-05-19)
Koolnapadol, N.
;
Promvonge, P.
;
Khanoknaiyakarn, C.
;
Promthaisong, P.
;
Hoonpong, P.
An experimental investigation was carried out to explore the thermal performance and frictional loss features in a solar air heater (SAH) channel that was intentionally roughened on the absorber surface using multiple inclined groove turbulators. The working fluid, air, flows into the SAH channel, which has a consistent surface heat flux for Reynolds numbers (Re) varying between 5290 and 22,600 in the current research. Thermal characteristics at a single inclination angle (a = 45°) are investigated in this research by comparing the effects of three distinct relative groove frequencies (P/H=PR=0.8, 1.2 and 1.6) and groove depth ratios (D/H=DR=0.16, 0.24 and 0.32). The findings highlight that the employ of inclined grooves results in a noticeable rise in Nusselt number (Nu) from 1.24 to 2.82 times relative to the smooth absorber plate (smooth channel), as well as a 1.88 to 7.9 times increase in friction factor (f). The Nu and f show an increasing trend when Re increases, whereas the opposite pattern occurs as DR and PR increase. At PR = 0.8 and DR = 0.32, the inclined groove roughness has the largest thermal effectiveness factor (TEF) of around 1.64. The Nu and f correlations, which are functions of inclined groove features, have also been established.
Some of the metrics are blocked by your
consent settings
Thermal performance augmentation in a solar air heater with twisted multiple V–baffles
(2024-11-01)
Chompookham, Teerapat
;
Eiamsa-ard, Smith
;
Buanak, Kalong
;
Promvonge, Pongjet
;
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.
Some of the metrics are blocked by your
consent settings
Effect of arc-shaped twisted-baffles on augmented heat transfer in a rectangular duct
(2023-02-01)
Promvonge, Pongjet
;
Phila, Arnut
;
Chuwattanakul, Varesa
;
Chokphoemphun, Suriya
;
Eiamsa-Ard, Smith
In this current work, the effect of utilizing arc-shaped twisted-baffles (T-ABs) in a rectangular air channel on thermal performance factor (TPF) has been experimentally studied. In these experiments, the influence of the changes in parameters such as dimensions of pitch ratio (p/w), attached arc-shape angle (α), and Reynolds number (Re) are explored. The comparisons demonstrate that a channel mounted with arc-shaped twisted-baffles yielded considerably greater Nusselt numbers than a smooth channel, possibly attributable to multiple-impinging jets near the channel surface. Heat transfer enhancements of twisted arc-shaped baffles (T-AB) having larger attack angles were superior to those having smaller attack angles. The one with α = 90o offered greater heat transfer rates than the ones with α = 20o, 40o, 60o, and 80o by approximately 8%, 7%, 4%, and 2%, respectively. The superior heat transfer was attributed to the better contact between the working fluid and heat transfer surfaces. In addition, utilizing arc-shaped twisted-baffles with the lowest p/w of 4.0, in a channel produced stronger vortices and multiple impinging jets, which caused better fluid mixing than other p/w. The optimum condition is achieved using T-ABs at an attached arc-shape angle of α = 90o, p/w = 4.0 and Re = 4000, where the heat transfer rate (Nu), friction factor (f) and TPF are found to be, respectively, 3.31, 4.68 and 1.98 times greater than those of a plain channel.
Some of the metrics are blocked by your
consent settings
Heat transfer augmentation in solar heat exchanger duct with louver-punched V-baffles
(2022-12-01)
Promvonge, Pongjet
;
Promthaisong, Pitak
;
Skullong, Sompol
A vortex generator's ability to create secondary flow and accelerate rapid fluid mixing allows it to effectively improve thermal performance in a solar heat exchanger duct. A newly created louver-punched V-baffle (LPVB) vortex generator was tested experimentally in the current study and the flow and thermal patterns were also investigated using a three-dimensional CFD simulation. The Realizable k–ε turbulence model was utilized in the simulation and the predictions were verified using experimental data and correlations. By directing the impinging air onto the duct's heated surface, the square louver on the baffle served the primary function of reducing pressure drag. Air was used as the test fluid, flowing at Reynolds numbers (Re) from 5300 to 23,000 into the constant heat-fluxed duct. On the heated wall that was set up by letting the V-apex direct upstream, the LPVBs with a 45° attack angle (α) were repeatedly positioned. There were two aspects to the current investigation. First, the optimal relative baffle pitches (P<inf>R</inf>) and louver angles (β) conditions were determined by looking at the LPVB characteristics, which included four β and three P<inf>R</inf> at a fixed relative louver size (L<inf>R</inf> = 0.5) and baffle height (B<inf>R</inf> = 0.4). Second, three relative louver sizes (L<inf>R</inf> = 0.3–0.9) were investigated at the optimal P<inf>R</inf> and β. According to the results, the solid-baffle friction loss is significantly reduced by the LPVB with β > 0° while the heat transfer is slightly lower. In the first part, the LPVB with P<inf>R</inf> = 1.5, β = 45° has the optimal performance while in the second part, the one with L<inf>R</inf> = 0.9 yields the greatest performance. A numerical flow model was computed to understand the flow and thermal patterns. The findings were verified using the available measurements, and there is close agreement between the experimental and numerical results.
Some of the metrics are blocked by your
consent settings
Numerical heat transfer in a solar air heater duct with punched delta-winglet vortex generators
(2021-08-01)
Promvonge, Pongjet
;
Promthaisong, Pitak
;
Skullong, Sompol
The flow topology and thermohydraulic performance of a novel designed punched delta-winglet (P-DW) placed on the absorber of a solar air heater duct are numerically explored. The effects of geometrical parameters, namely, the relative winglet pitch, PR = 1-2 and the relative punched hole size, dR = 0-0.583 at a single value of blockage ratio, BR = 0.48 and attack angle, α = 30° on thermal characteristics are proposed for Reynolds number from 4000 to 24,000. Among several turbulence models, the simulation has shown that the realizable k-ϵ turbulence model is favorable with respect to measurements. For flow patterns, the P-DW produces several counter-spinning vortices helping induce the impinging jets onto the absorber surface whilst for thermal behaviors, the decline of PR and dR leads to the rise in the friction factor (f) and Nusselt number (Nu). The P-DW provides greater Nu and f than the plain flat plate by 17.1-78.21 and 3.92-5.9 times, respectively and gives the highest performance around 2.1. Further, the P-DW is modified by covering the punched hole partially with a circular flap, called the flapped delta-winglet (F-DW) and this F-DW yields the greatest performance around 2.16 higher than the P-DW about 2.9%.
Some of the metrics are blocked by your
consent settings
Performance evaluation of solar receiver heat exchanger with rectangular-wing vortex generators
(2020-01-01)
Koolnapadol, Narin
;
Promvonge, Pongjet
;
Skullong, Sompol
The paper presents an experimental investigation on heat transfer and flow resistance in a solar air heater (SAH) duct with rectangular-wing vortex generators (RWVGs) on the absorber plate to increase the SAH system performance. The experimental work is carried out in the test duct with its aspect ratio (AR) of 10 for Reynolds number (Re) based on the hydraulic duct diameter ranging from 5290 to 22,700. The RWVGs are placed on the absorber with three attack angles (α=30°45°and 60°) and three relative wing pitches (P<inf>R</inf> = P<inf>l</inf>/H = 1.0, 1.5 and 2.0) at a single relative wing height (B<inf>R</inf>=b/H=0.67). The experimental result shows that the use of RWVGs leads to the considerable increase in Nusselt number (Nu) over the flatplate duct (smooth duct) around 4.06-5.79 times while the increase in friction factor (f) is about 11.43-43.97 times. The Nu and f display the increasing trend with the rise of α but show the opposite trend for the increment of P<inf>R</inf>. The highest thermal performance for using the RWVG roughness is some 1.95 at α=30°and P<inf>R</inf> = 1.5. Correlations for Nu and f have also been developed and determined as a function of RWVG parameters.
Some of the metrics are blocked by your
consent settings
Heat transfer in solar receiver heat exchanger with combined punched-V-ribs and chamfer-V-grooves
(2019-11-01)
Promvonge, Pongjet
;
Skullong, Sompol
An experimental work has been carried out to investigate the influence of combined turbulence promoters (or turbulators) on forced convection and fluid flow resistance behaviors in a solar air heater duct. Two turbulators included V-ribs with punched holes and chamfered V-grooves were introduced. The V-rib and the V-groove having the attack angle of 45° were mounted repeatedly on the absorber plate with their arrangements for V-tip pointing upstream and pointing downstream. Air as the test fluid flowed into the duct with Reynolds number (Re) ranging from 5300 to 23,000. The rib parameters were three relative rib-pitches (R<inf>P</inf> = 1.0, 1.5 and 2.0), three inclination angles (β = 45°, 0° and −45°) of rib-punched holes having a single relative rib height or blockage ratio, R<inf>B</inf> = 0.5. The groove parameters included three relative groove-pitch lengths (R<inf>P</inf> = 1.0, 1.5 and 2.0) similar to the V-rib case. Influences of this newly designed absorber plate on Nusselt number (Nu) and friction factor (f) have been examined and compared with similar results of the smooth duct alone. The experimental results demonstrated that the combined turbulators at β = 45° and R<inf>P</inf> = 1.0 provide the maximum Nu and f, especially for the V-up case due to stronger vortex flows and the impinging flows from the punched holes over the absorber plate. Further, a new thermal enhancement factor (TEF) at similar pumping power has been proposed and it indicates that the combined V-up rib-groove with β = 45° and R<inf>P</inf> = 1.5 has the highest TEF of about 2.47.
Some of the metrics are blocked by your
consent settings
Thermal performance in solar air heater with perforated-winglet-type vortex generator
(2018-08-01)
Skullong, Sompol
;
Promthaisong, Pitak
;
Promvonge, Pongjet
;
Thianpong, Chinaruk
;
Pimsarn, Monsak
An experimental and numerical study of turbulent convective heat transfer in a solar air heater duct with winglet-type vortex generators (WVGs) placed on the absorber plate is presented. Air as the test fluid enters the duct having a uniform wall heat-flux applied on the upper wall or the absorber plate with Reynolds number from 4100 to 25,500. Two types of WVGs are introduced: rectangular (RWVG) and trapezoidal (TWVG) WVGs, in order to create multiple vortex flows along the duct. The WVG parameters in the present study include two relative height (B<inf>R</inf> = e/H = 0.2 and 0.48), three longitudinal pitch ratios (P<inf>R</inf> = P<inf>l</inf>/H = 1, 1.5 and 2) and a single attack angle, α = 30°. The experimental result reveals that the RWVG with B<inf>R</inf> = 0.48 and P<inf>R</inf> = 1 provides the highest heat transfer and friction factor at about 7.1 and 109.5 times above the flat duct, respectively while the TWVG with B<inf>R</inf> = 0.2 and P<inf>R</inf> = 1.5 yields the maximum thermal performance around 1.84. Then, to improve the performance by reducing the substantial pressure loss, both the WVGs with B<inf>R</inf> = 0.48 and P<inf>R</inf> = 1.5 are modified to be perforated rectangular and trapezoidal winglet-type vortex generators (P-RWVG and P-TWVG) with four different punched hole/pore diameters (d = 1, 3, 5 and 7 mm) on their central area. The investigation indicates that among the perforated WVGs, the P-RWVG at d = 1 mm yields the highest heat transfer and friction factor up to 6.78 and 84.32 times higher than the smooth duct but the best thermal performance of about 2.01 is found for the P-TWVG with d = 5 mm. To explore the flow and heat transfer pattern, a 3D numerical flow simulation is performed and validated with available measurements where both the numerical and measured results are in good agreement.
Some of the metrics are blocked by your
consent settings
Performance assessment of solar air heater duct roughened with perforated-winglet vortex generators
(2017-01-01)
Koolnapadol, Narin
;
Promvonge, Pongjet
;
Skullong, Sompol
An experimental study has been conducted to investigate heat transfer, friction loss and thermal performance characteristics of turbulent flow in a solar air heater channel artificially roughened on one side (absorber plate) with multiple perforated-winglet vortex generator (PWVG). Air as the working fluid enters the test duct having a uniform surface heat-flux with Reynolds number (Re) ranging from 5200 to 24,000 in the present work. Effects of four different punched hole/pore diameters of winglet (d=2 mm, 4 mm, 6 mm and 8 mm) at a single relative winglet height (RB=b/H=0.6), relative winglet pitch (RP=P/H=3) and attack angle (β= 60°) on thermal characteristics are examined. The experimental results show that the PWVG provides the drastic increase in Nusselt number (Nu) and friction factor (f) values over the flat/smooth channel. In addition, substantial increases in Nu and f values are found for the rise in hole sizes. The maximum Thermal Enhancement Factor (TEF) is found for the pore diameter of 2 mm at lower Reynolds number. The present results are also compared with the results from the typical or solid winglet, TWVG (non-punched hole of winglet).

KMITL

Browse

Filters

Settings

Sort By

Results per page

Search Results