KMITL

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

Browse

Search Results

Now showing 1 - 4 of 4

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
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
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.

KMITL

Browse

Filters

Settings

Sort By

Results per page

Search Results