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Effect of trapezoidal louvered winglets on increased heat transfer and exergy in tubular heat exchanger
(2024-10-01)
Promvonge, Pongjet
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Thianpong, Chinaruk
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Jayranaiwachira, Nuthvipa
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Nakhchi, Mahdi Erfanian
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Skullong, Sompol
The effect of inserting a trapezoidal louvered winglet tape (TLWT) into a uniformly heat-fluxed tube on its thermal effectiveness was studied experimentally. The exergy and entropy analyses for turbulent flows, as well as frictional loss and thermal features, were highlighted as key aspects of the experimental finding for the Reynolds number which measured between about 4700 and 30,000. Because fixing baffles to the curved shape of tube wall presented a challenge, the baffles were consequently positioned on double surfaces of a flat tape. Six values of the louver angle (θ<inf>1</inf> = 0°, 25°, 30°, 45°, 60°, and 90°) and three values of the relative pitch of winglet (P<inf>R</inf> = 1.0, 1.5, and 2.0) were employed in the arrangement of TLWTs, with the V-apex oriented upstream (V-up). Each of these had only a fixed height (B<inf>R</inf> = 0.25) and angle of attack (α = 30°). The winglets were utilized to induce streamwise vortices which can hinder the boundary layer formation, while the louvered openings were adopted to lessen pressure drop without significantly impacting the primary vortices. The experiment results disclosed that the smallest θ<inf>1</inf> and P<inf>R</inf> produced the largest relative friction factor (f<inf>R</inf>) and Nu<inf>R</inf>, which were about 13.57 and 4.04 times higher, while P<inf>R</inf> = 1 and θ<inf>1</inf> = 45° provide the greatest TEF of about 2.27. The greatest exergy efficiency (η<inf>Ex</inf>) resulting from the TLWT was reached at θ<inf>1</inf> = 0°, but the generation of entropy (S˙<inf>g</inf><sup>′</sup>) dropped with lowering θ<inf>1</inf> and Re. A further examination, however, showed that the best scenario with α = 60° and staggered arrays is more desirable since it yields the largest TEF of 2.45 at θ<inf>1</inf> = 45° and P<inf>R</inf> = 1. For the range of parameters under consideration, the Nu and f correlations were additionally established.
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Evaluation of aerothermal performance of a round tube with regularly-spaced multi-channel twisted tape elements installed
(2024-06-01)
Phila, Arnut
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Chuwattanakul, Varesa
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Thianpong, Chinaruk
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Bhattacharyya, Suvanjan
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Naphon, Paisarn
This article presents a study of aerothermal performance of tubes with regularly-spaced multi-channel twisted tape elements (RS-MTT) installed. This research aimed to find the proper design RS-MTTs that induce swirl flow which potentially improves fluid mixing between the core fluid and the fluid near the tube wall, thereby accelerating the heat transfer rate. Additionally, the effects of Reynolds numbers and free-spacing ratios (s/y) on heat transfer, friction loss, and thermal performance behaviors were examined. The RS-MTTs having different free-spacing ratios (s/y) of 0.0, 0.25, 0.5, 0.75, and 1.0 were tested. Air was utilized as the testing fluid in experiments with Reynolds numbers (Re) spanning from 6000 to 20,000. The utilization of RS-MTTs with s/y = 0.0, 0.25, 0.5, 0.75, and 1.0 augmented heat transfer rates up to 1.74, 1.80, 1.85, 1.90, and 2.15 times given by the plain tube alone while the friction factors increased by 4.22, 4.61, 3.87, and 4.05 times, respectively. At the lowest Reynolds number of 6000, the thermal enhancement factors of the tube containing the RS-MTTs with s/y = 0.0, 0.25, 0.5, 0.75, and 1.0 reached the maximum values of 1.42, 1.35, 1.31, 1.27, and 1.23, respectively. Among the RS-MTTs tested, the RS-MTT with s/y = 0.0 showed the best thermal enhancement factor of 4.56%, corresponding to the heat transfer augmented of 11.52% with a friction penalty of 8.71%.
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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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Enhanced heat transfer performance in channel with delta-wing perforated V-type baffles
(2023-10-01)
Eiamsa-ard, Smith
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Phila, Arnut
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Thianpong, Chinaruk
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Chuwattanakul, Varesa
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Maruyama, Naoki
The article examines the influence of delta-wing V-type baffles (DW-PVBs) on the average Nusselt number, local Nusselt number distribution, pressure losses, and thermal performance behaviors in a channel. Delta-wing perforated V-type baffles (DW-PVBs) mounted in a regular manner on the bottom of a channel produced two pairs of longitudinal counter-rotating vortices to enhance chaotic fluid mixing and destabilize the boundary layer, hence boosting the heat transfer. The geometric characteristics of the delta-wing V-type baffle (DW-PVBs) located on the bottom of the channel were examined at relative baffle blockage and pitch ratios (BR = h/H = 0.3 and p/H = 1.5), and five delta-wing attack angles, θ = 0<sup>o</sup> (solid V-shaped baffle), 22.5°, 45°, 67.5°, and 90°. The present DW-PVBs mounted on the channel were designed to mitigate pressure loss due to flow blockage. The experiment was done by permitting air to flow through a channel at Reynolds numbers (Re) ranging from 6000 to 24,000. The present results show that the friction factor using the DW-PVBs decreased considerably with increasing θ values. The experimental results revealed that small θ values yielded greater heat transfer and resistance than large θ values. The DW-PVBs with θ = 22.5° performed better than inserts with other θ values in terms of heat transfer rate. It was also observed that the DW-PVBs with θ = 45° gave the maximum thermal performance factor (TPF), while presenting a 13.64–17.26% lower friction factor than the solid V-shaped baffle. Furthermore, it was also found that the DW-PVBs with θ = 0°, 22.5°, 45°, 67.5°, and 90° gave peak TPF values of up to 1.87, 1.89, 1.91, 1.87, and 1.84 at the lowest Reynolds number, 6000.
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Influence of sawtooth twisted tape on thermal enhancement of heat exchanger tube
(2023-03-01)
Samutpraphut, Boonsong
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Eiamsa-ard, Smith
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Chuwattanakul, Varesa
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Thianpong, Chinaruk
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Maruyama, Naoki
This article employs sawtooth twisted tapes to generate swirling flow and interrupted flowing disturbance in order to increase the level of heat transfer rate. The influences of the sawtooth twisted tape (S-TT) on enhanced heat transfer rate, friction factor and aerothermal performance index (API) behaviors are analyzed. The sawtooth twisted tapes (S-TTs) possessing constant pitch/twist ratio (y//W) of 3.0 and six sawtooth angles (α) of 20°, 30°, 40°, 50°, 60°, and 70° are assessed. Considering turbulent flow using air as the testing fluid, experiments were investigated at 6,000 < Re < 20,000 under boundary conditions of constant heat flux. According to the experimental findings, sawtooth twisted tape (S-TT) improves heat transfer rate and raises pressure loss with varying rates based on sawtooth angles (α). With the sawtooth twisted tape (S-TT) and 70° sawtooth angles, the optimum API of 1.33 is attained, while Nusselt number and friction factor are 32 and 0.135 at Re = 6,000. The recommended sawtooth twisted tape (S-TT) yields a highest Nusselt number of 78, which is 1.6 times greater than the typical twisted tape (TT) and 1.1 times greater than the plain tube. The combination of the TT and sawtooth patterns can be beneficial in terms of boosting heat transfer rate and API relating coupling of swirling flow and interrupted flowing disruption effects since the sawtooth twisted tape (S-TT) offers superior performance than the TT. Additionally, the heat exchanger tubes fitted with sawtooth twisted tape (S-TT) at sawtooth angles (α) of 20°, 30°, 40°, 50°, 60°, and 70° gain greater Nusselt number than the plain tube up to 158.3%, 162.2%, 166.1%, 171.7%, 179.7% and 186.2%, respectively.
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Thermal-hydraulic performance of solar receiver duct with inclined punched-ribs and grooves
(2022-11-01)
Jayranaiwachira, Nuthvipa
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Promvonge, Pongjet
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Thianpong, Chinaruk
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Skullong, Sompol
The article presents an experimental study on turbulent airflow friction and thermal behaviors in a solar receiver heat exchanger duct mounted with combined inclined chamfered-groove and turbulators. The experimental work was conducted for Reynolds numbers from 5,300 to 24,000, based on the hydraulic duct diameter. The 45°-inclined punched-ribs and grooves were placed periodically on the absorber plate. The punched-rib parameters were four inclination angles (β = 0°, 45°, 90° and 135°) of the punched holes and three relative rib pitches (PR = 1, 1.5 and 2) whereas only a rib blockage ratio (BR = 0.5) and an angle of attack (α) of 45° were fixed. Similarly, the parameters of the grooves included only three groove-pitch ratios (PR), similar to the rib pitches and one groove blockage ratio (BR = 0.2). The experimental result has revealed that the combination of rib-groove turbulators at β = 0° (solid rib) and PR = 1 gives the maximum heat transfer rate and friction loss while the greatest thermal enhancement factor of 2.1 was found at β = 45°, PR = 1. Moreover, the friction loss and heat transfer correlations for this thermal system were determined.
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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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Heat transfer characterization in a tubular heat exchanger with V-shaped rings
(2017-01-05)
Chingtuaythong, Witoon
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Promvonge, Pongjet
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Thianpong, Chinaruk
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Pimsarn, Monsak
This article presents the influence of V-shaped rings (or V-ring) placed in a uniform heat-fluxed tube on heat transfer and flow resistance characteristics. In the current experiment, the V-ring elements with attack angle of 30° are inserted into the tube with four relative ring-pitches (R<inf>P</inf> = P/D = 0.5, 1.0, 1.5 and 2.0) and three ring blockage ratios (R<inf>B</inf> = e/D = 0.1, 0.15 and 0.2). Air as the test fluid flows through the tube for Reynolds number of about 5000–25,000. The experimental results reveal that the V-ring can considerably enhance the heat transfer rate up to 5.8 times above the plain tube whereas the friction factor is up to 82 times. The increase in R<inf>B</inf> leads to higher heat transfer and friction loss while the increment in R<inf>P</inf> provides the reversing trend. The thermal enhancement factor of the V-ring is in the range of 1.36–1.63 where its maximum regarded as the optimum point is at R<inf>B</inf> = 0.1 and R<inf>P</inf> = 1.0. In comparison with other vortex-flow devices, the V-ring yields much higher thermal performance than the published inclined rings, wire-coils and twisted tapes. Nusselt number and friction factor correlations for the V-ring are also determined.
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Thermal characterization in a circular tube fitted with inclined horseshoe baffles
(2015-01-22)
Promvonge, Pongjet
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Tamna, Sombat
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Pimsarn, Monsak
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Thianpong, Chinaruk
In the present study, the influence of inclined horseshoes baffles placed repeatedly in a tubular heat exchanger on heat transfer rate, friction factor and thermal enhancement factor are experimentally determined. The horseshoe baffle elements with an inclination angle of 20° were inserted periodically into the test tube at three different baffle-pitch ratios (P<inf>R</inf> = 0.5, 1.0 and 2) and -width or blockage ratios (B<inf>R</inf> = 0.1, 0.15 and 0.2). The experiment was conducted in the test tube having a uniform heat-fluxed wall by varying turbulent airflow to obtain Reynolds number in a range of 5300-24,000. The experimental results revealed that the tube fitted with inclined horseshoes baffles provides considerable improvement of the heat transfer rate over the plain tube around 92-208% while the friction factor is increased at about 1.76-6.37 times. To access the real benefits for the inclined horseshoes baffles inserted in plain tube, thermal performance factor is examined and found to be in the range of 1.34-1.92 at which the maximum obtained at P<inf>R</inf> = 0.5 and B<inf>R</inf> = 0.1 is considerably higher than that for published inserted devices. Correlations for Nusselt number and friction factor for the oblique horseshoe-baffled tube are also proposed.
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Heat transfer behaviors in a solar air heater channel with multiple V-baffle vortex generators
(2014-12-01)
Tamna, Sombat
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Skullong, Sompol
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Thianpong, Chinaruk
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Promvonge, Pongjet
The article presents a study on heat transfer augmentation in a solar air heater channel fitted with multiple V-baffle vortex generators (BVG). During the test air was passed through the test channel under a uniform wall heat-flux of the absorber plate. The fluid flow and heat transfer characteristics are presented for Reynolds numbers based on the channel hydraulic diameter ranging from 4000 to 21,000. The V-baffles are applied at a relative baffle height (in terms of blockage ratio, BR. =. b/. H=. 0.25) and attack angle of 45° with respect to the main flow direction. The use of BVG in the channel is to generate multiple longitudinal vortex flows through the test channel to increase turbulence intensity and stronger mixing of fluid between the core and the near-wall flow. Influences of three different baffle-pitch to channel-height ratios (PR. =. P/. H=. 0.5, 1 and 2) on heat transfer and pressure drop in terms of respective Nusselt number and friction factor (or energy loss for propelling air through the channel) are examined. Three BVG arrangements, namely, one BVG wall (or single BVG), in-line and staggered BVGs on two opposite walls are also investigated. The experimental result reveals that the smaller PR provides the highest heat transfer and friction factor for all BVGs. The in-line BVG yields higher heat transfer and friction loss than the staggered and the single BVG. However, the single BVG with PR. =. 0.5 yields the highest thermal performance. To shed light of heat transfer mechanism, a numerical work is also conducted to investigate heat transfer and flow friction characteristics in the channel fitted with 45° BVGs and in comparison, the numerical results are in good agreement with experimental data.

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