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Influence of divergence tapered V-baffles on heat transfer behaviors in a rectangular channel
(2026-05-15)
Keaitnukul, Warin
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Pingta, Supapat
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Phila, Arnut
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Wongcharee, Khwanchit
;
Maruyama, Naoki
This study examines the effects of Divergence Tapered V-Baffle (henceforth DT-VB) regarding the heat transfer and friction loss behavior within the rectangle-shaped duct. The baffle attack angles (α) were set at 45°, 60°, 75°, and 90°. The experimental results indicated that as Reynolds numbers increased, the Nusselt numbers exhibited an upward trend, while the friction values showed a corresponding decrease. The Nusselt number improved consistently as the attack angle decreased, with baffles at a 60° attack angle producing the highest friction loss, followed by those at 45°, 75°, and 90°. Among the configurations tested, the 45° attack angle demonstrated the best thermal performance due to its relatively low friction loss and enhanced heat transfer. The highest thermal performance factor (TPF) of 2.13 was attained at a 45° attack angle and a Reynolds number of 6,000.
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Effect of arc-shaped twisted-baffles on augmented heat transfer in a rectangular duct
(2023-02-01)
Promvonge, Pongjet
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Phila, Arnut
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Chuwattanakul, Varesa
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Chokphoemphun, Suriya
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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.
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Heat transfer visualization of swirling impinging jets using nozzle with centrally hollow helical-tape
(2020-05-01)
Eiamsa-Ard, Smith
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Kunnarak, Kengkla
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Wongcharee, Khwanchit
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Chuwattanakul, Varesa
The present research was conducted to determine the heat transfer visualization of swirling impinging jets (SIJs) induced by nozzle with centrally hollow helical-tape using a thermochromic liquid crystal (TLC) sheet. The effects of jet-to-plate spacing ratios (L/D= 2.0, 4.0, 6.0 and 8.0) and Reynolds numbers (10,000 Re 20,000) on the radial uniformity and intensity of convective heat transfer were investigated. The experimental results of SIJs were compared with those of conventional impinging jets (CIJs). The formation of swirl flow of swirling impinging jet (SIJs) helped in improving the uniformity of local heat transfer or Nusselt number (Nu) and also average Nusselt number, as compared to those of conventional impinging jets (CIJs). Furthermore, the average Nusselt number (Nu) increased as jet-to-plate spacing ratio (L/D) decreased while Reynolds number (Re) increased for both conventional impinging jets (CIJs) and swirling impinging jets (SIJs). The highest Nusselt number (Nu) of swirling impinging jet (SIJ) was obtained at the jet-to-plate spacing ratio (L/D) of 4.0 and Reynolds number (Re) of 20,000. The maximum Nusselt number (Nu) of swirling impinging jet (SIJ) was higher than that of conventional impinging jets (CIJs) at similar conditions by around 5.3%.
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Thermal and swirl flow topologies in a twisted square duct with a multi-twisted tape installed
(2020-01-01)
Promthaisong, Pitak
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Chuwattanakul, Varesa
;
Eiamsa-Ard, Smith
This paper presents 3D numerical investigation of the turbulent flow and heat transfer characteristics of a twisted square duct installed with multi-twisted tapes. Air was used as the working fluid with flow rates in terms of Reynolds numbers ranging from 3000 to 20,000. The effects of (1) multi-twisted tape width ratios (w/H) of 0.2 to 1.0 and (2) the number of channels (N = 2 and 4) on heat transfer and flow mechanisms were studied at constant twist ratio of y/D = 3.5. The numerical results showed that twisted square duct combined with twisted tape caused swirl flows which effectively promoted fluid mixing and provided heat transfer over those of both a straight smooth square duct and twisted square duct. Increasing w/H led to increases in both heat transfer and the friction factor. At a given multi-twisted tape width ratio (w/H), the heat transfer and friction factor with N = 4 were higher than those with N = 2, while thermal enhancement factor showed the opposite trend. A maximum thermal enhancement factor of 1.93 was obtained at tape width ratio of w/H = 1.0, channel number of N = 2 and Re = 3000.
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Thermo-hydraulic performance of round tubes installed with double V-shaped winglet vortex generators: Effect of blockage ratio
(2020-01-01)
Samruaisin, Prachya
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Samutpraphut, Boonsong
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Wongcharee, Khwanchit
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Eiamsa-Ard, Smith
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Saysroy, Anucha
Double V-shaped winglet vortex generators is proposed in the present research enhancing heat transfer and thermal-hydraulic performance factor. The numerical simulation was performed to study the effects of blockage ratios (e/D = 0.05-0.15) and Reynolds numbers (Re = 5000-15,000) on heat transfer rate, flow structure, local heat transfer, pressure loss and thermal-hydraulic performance factor characteristics. The double V-shaped winglets were installed in tandem arrangement on the top and bottom of tubes with constant pitch ratio of p/D = 1.0. Water was employed as the working fluid for Reynolds numbers ranging from 5000 to 15,000 under constant wall temperature boundary conditions. The numerical results demonstrated that the vortex generators induced swirling motion which helped in improving fluid flow mixing, leading to heat transfer enhancement with a moderate pressure loss penalty. Heat transfer and friction loss increased with increasing blockage ratio and Reynolds number while thermal-hydraulic performance factor showed opposite trend. The maximum thermal-hydraulic performance factor of 1.89 was obtained by using the vortex generator with the smallest blockage ratio (e/D) of 0.05 at the lowest Reynolds number of 5000.
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Influence of geometric parameters of alternate axis twisted baffles on the local heat transfer distribution and pressure drop in a rectangular channel using a transient liquid crystal technique
(2019-01-01)
Phila, Arnut
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Thianpong, Chinaruk
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Eiamsa-Ard, Smith
This paper reports the effects of alternate axis twisted baffle geometric parameters on the heat transfer and flow characteristics within rectangular channels. In our experiments we used modified shapes of alternate axis twisted baffles according to relative pitch ratios (s/w) equal to 2-12 and twist ratios (y/w) equal to 1-5, under conditions where the angle of attack (a) was 90 and the relative blockage height (e/Dh) was at a constant value of 0.095. The results for the Reynolds numbers based on the duct hydraulic diameter ranged from 9000 to 24,000 at a constant Prandtl number, Pr = 0.707, using air as a working fluid. A 0.05 mm thick stainless-steel foil was used as a heater, and a thermochromic liquid crystal technique was used to obtain the local temperature distribution on the heated surfaces. Images were captured in areas with periodic, fully developed regions in the channel. The results show that rectangular channels equipped with alternate axis twisted baffles demonstrated 80%-185% greater heat transfer than rectangular channels with no baffles. Channels with alternate axis twisted baffles at higher twist ratios (y/w) and smaller relative pitch ratios (s/w) showed increased heat transfer, as well as pressure loss within the system, compared with other types of twisted baffles. The thermal enhancement factor of the rectangular channels equipped with alternate axis twisted baffles was higher than that for transverse baffles and smooth channels under similar operating conditions.
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Impingement cooling by round jet with longitudinal swirling strip
(2018-03-01)
Kunnarak, Kengkla
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Somravysin, Prachya
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Eiamsa-Ard, Smith
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Chuwattanakul, Varesa
The objective of this research is to study the effect of swirling impinging jet on the heat transfer in the impinged plated by using thermochromic liquid crystal (TLC) sheet. In the experiments, the nozzle having a diameter of 20 mm (D) was installed with four-channel twisted tape as a longitudinal swirling strip. The jet impingement was performed at jet-to-plate distances (L/D) of 2, 3, 4, 5, 6 and 7, and constant Reynolds number (Re) of 5000. The experimental results showed that the swirling jet induced by the four-channel twisted tape gave higher heat transfer rates than the conventional jet at the same operating conditions. The highest average heat transfer rate was obtained at the jet-to-plate distance (L/D) of 2.
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Effect of geometrical parameters on turbulent flow and heat transfer behaviors in triple-start corrugated tubes
(2018-01-01)
Promthaisong, Pitak
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Jedsadaratanachai, Withada
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Eiamsa-Ard, Smith
Computational results of flow structure, pressure loss and heat transfer characteristics in triple-start corrugated tubes are reported. The influences of the depth ratio (DR = 0.02, 0.04, 0.06, 0.08, 0.1, 0.12, 0.14 and 0.16) and pitch ratio (PR = 0.5, 0.65, 0.75, 1.0, 1.5 and 2.0) were investigated in turbulent flow regime, Re = 5000 to 20,000. The computational results indicated that the triple-start corrugated tubes generate main swirl flow and helical swirl flow which helps to reduce the thermal boundary layer thickness and enhance the heat transfer rate. The flow and heat transfer become under fully developed periodic condition around x/D = 6.0. The friction factor monotonically increases with the rise of DR values and decrease PR values while maximum heat transfer rate is found at DR = 0.08 and PR = 0.75. Nusselt numbers and friction factors of triple-start corrugated tubes in the investigated range are found to be 0.8 to 2.31 and 1.0 to 17.14 times over those of the straight circular smooth tube, respectively. For the range studied, the triple-start corrugated tube with DR = 0.06 and PR = 0.75 offers the maximum thermal enhancement factor of 1.21 at Re = 5000.
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Influence of delta-winged dual twisted tapes insertion on heat transfer and pressure drop characteristics
(2015-01-01)
Samruaisin, Prachya
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Changcharoen, Wayo
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Chuwattanakul, Varesa
;
Eiamsa-Ard, Smith
The article presents the heat transfer and friction factor characteristics of turbulent flow in a uniform wall heat flux tube inserted with delta-winged dual twisted tapes. The typical dual twisted tapes (DTs) with constant twist ratio of y/W = 3.0 and delta-winged dual twisted tapes with delta-winged attack angle of α = 30° and β = 30° were carried out. Influences of the delta-winged arrangements in (1) the parallel direction (DT-PW) and (2) the counter direction (DT-CW) on the thermal performance characteristics were also described. The experimental results found that the use of the dual twisted tapes with parallel wing arrangements (DT-PW) provide the heat transfer higher than those the typical dual twisted tapes (DTs) and dual twisted tapes with counter wing arrangements (DT-CW) around 6.6-7.3% and 5.5-8%, respectively, due to stronger of dual-swirling/turbulent flow leading to better fluid mixing between the core and near tube walls while the friction factor is increasing up to 10.9 times above the plain tube. The typical dual twisted tapes (DTs), dual twisted tapes with parallel wing arrangements (DT-PW) and dual twisted tapes with counter wing arrangements (DT-CW) performs the highest thermal performance factor up to 1.2, 0.9 and 0.85 at Reynolds number of 6000.
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Thermal behaviors in a solar air heater channel with arc-shaped baffle turbulators
(2014-01-01)
Koolnapadol, Narin
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Kaewkohkiat, Yingyong
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Promvonge, Pongjet
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Eiamsa-Ard, Smith
Influences of arc-shaped baffles turbulators (ASB) on thermal behaviors in a solar air heater channel are studied. In the experiment, the ASB with three pitch ratios (P/e) are placed on the absorber plate (bottom channel wall in this case) to generate stronger turbulence intensity in the channel. The distributions of temperature and local Nusselt number contours in the absorber plate fitted with ASB are observed with thermochromic liquid crystal (TLC) sheet. The results reveal that the heat transfer increases with the decrease in P/e due to longitudinal vortex flow effect. The heat transfer from employing the ASB at P/e = 4.0, 6.0 and 8.0 is higher than the smooth channel around 116%, 120% and 127%, respectively. This indicates that the ASB pitch spacing is optimal at 8 times baffle height in the present work.

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