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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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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 performance in square-duct heat exchanger with quadruple V-finned twisted tapes
(2015-12-05)
Promvonge, Pongjet
An investigation on heat transfer augmentation in a square duct with insertion of combined 30°V-fins and quadruple counter-twisted tapes is conducted experimentally. Air as the working fluid enters the test duct having a uniform wall heat-flux condition with Reynolds number ranging from 4000 to 30,000 in the present work. The combined vortex generators (called "V-finned counter-twisted tape") are obtained by incorporating V-fins into the edges of quadruple twisted-tapes having a similar twist ratio of 4. The effect of pertinent V-fin parameters such as four relative fin height, (R<inf>B</inf> = e/w = 0.16, 0.21, 0.32 and 0.42) and relative fin pitch, (R<inf>P</inf> = P/w = 4, 8, 12 and 16) at a single fin attack angle, α = 30°on thermal characteristics is examined. The experimental results reveal that the heat transfer and pressure drop in the form of respective Nusselt number and friction factor from the V-finned counter-twisted tape tend to increase with the rise of R<inf>B</inf> but show the reversing trend with increasing R<inf>P</inf>. The thermal performance of the V-finned counter-twisted tape is considerably higher than that of the quadruple twisted tapes alone. The V-finned counter-twisted tape with R<inf>B</inf> = 0.42 and R<inf>P</inf> = 4 yields the maximum Nusselt number and friction factor but the one with R<inf>B</inf> = 0.21 and R<inf>P</inf> = 4 provides the highest thermal performance of about 1.75 at lower Reynolds number.
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Thermal performance of tubular heat exchanger with multiple twisted-tape inserts
(2015-05-01)
Chokphoemphun, Suriya
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Pimsarn, Monsak
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Thianpong, Chinaruk
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Promvonge, Pongjet
The paper presents an experimental investigation on enhanced heat transfer and pressure loss characteristics by using single, double, triple, and quadruple twisted-tape inserts in a round tube having a uniform heat-fluxed wall. The investigation has been conducted in the heat exchanger tube inserted with various twisted-tape numbers for co- and counter-twist arrangements for the turbulent air flow, Reynolds number (Re) from 5300 to 24000. The typical single twisted-tape inserts at two twist ratios, y/w = 4 and 5, are used as the base case, while the other multiple twisted-tape inserts are at y/w = 4 only. The experimental results of heat transfer and pressure drop in terms of Nusselt number (Nu) and friction factor (f), respectively, reveal that Nu increases with the increment of Re and of twisted-tape number. The values of Nu for the inserted tube are in a range of 1.15-2.12 times that for the plain tube while f is 1.9-4.1 times. The thermal enhancement factor of the inserted tube under similar pumping power is evaluated and found to be above unity except for the single and the double co-twisted tapes. The quadruple counter-twisted tape insert provides the maximum thermal performance.
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Heat transfer augmentation in a circular tube with winglet vortex generators
(2015-04-01)
Chokphoemphun, Suriya
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Pimsarn, Monsak
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Thianpong, Chinaruk
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Promvonge, Pongjet
The article presents the influence of winglet vortex generators (WVGs) placed in the core flow area on thermal performance enhancement of a tube heat exchanger. The experiment was carried out in a uniform wall heat-fluxed tube by varying turbulent airflow for Reynolds number ranging from 5300 to 24000. In the present work, the WVGs with an attack angle of 30° were inserted into the test tube at four different winglet pitch ratios (R<inf>P</inf> = P/D) and three winglet-width or blockage ratios (R<inf>B</inf> = e/D). The experimental results at various R<inf>P</inf> and R<inf>B</inf> values were evaluated and compared with those for smooth tube and tubes with twisted tape or wire coil. The measurement reveals that the WVGs enhance considerably the heat transfer and friction loss above the plain tube, wire coil and twisted tape. The Nusselt number and friction factor increase with the increment of R<inf>B</inf> and Re but with the decreasing R<inf>P</inf>. The average Nusselt numbers for the WVGs with various R<inf>B</inf> are in the range of 2.03-2.34 times above the plain tube. The thermal performance for the WVGs is found to be much higher than that for the wire coil and twisted tape and is in a range of 1.35-1.59. Also, a numerical investigation is conducted to study the flow structure and heat transfer enhancement mechanisms in the winglet-inserted tube.
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Enhanced heat transfer in a heat exchanger square-duct with discrete V-finned tape inserts
(2015-03-01)
Noothong, Watcharin
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Suwannapan, Supattarachai
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Thianpong, Chinaruk
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Promvonge, Pongjet
The article presents an experimental and numerical study on thermal performance enhancement in a constant heat-fluxed square-duct inserted diagonally with 45° discrete V-finned tapes (DFT). The experiments were carried out by varying the airflow rate through the tested square duct with DFT inserts for Reynolds number from 4000 to 25000. The effect of the DFT with V-tip pointing upstream at various relative fin heights and pitches on heat transfer and pressure drop characteristics was experimentally investigated. Both the heat transfer and pressure drop were presented in terms of Nusselt number and friction factor respectively. Several V-finned tape characteristics were introduced such as fin- to duct-height ratio or blockage ratio (R<inf>B</inf> = e/H = 0.075, 0.1, 0.15 and 0.2), fin pitch to duct height ratio (R<inf>P</inf> = P/H = 0.5, 1.0, 1.5 and 2.0) and fin attack angle, α = 45°. The experimental results reveal that the heat transfer and friction factor values with DFT inserts increase with the increment of R<inf>B</inf> but the decrease of R<inf>P</inf>. The inserted square-duct at R<inf>B</inf> = 0.2 and R<inf>P</inf> = 0.5 provides the highest heat transfer and friction factor while the one with R<inf>B</inf> = 0.1 and R<inf>P</inf> = 1.5 yields the highest thermal performance. Also, a numerical simulation was conducted to investigate the flow structure and heat transfer mechanism inside the tested duct with DFT inserts.
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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 augmentation in a round tube with 60° winglet pair inserts
(2014-01-01)
Chokphoemphun, Suriya
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Tongyote, Pattarapan
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Promvonge, Pongjet
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Jedsadaratanachai, Withada
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Chompookham, Teerapat
The experimental study on heat transfer enhancement in a tubular heat exchanger fitted with 60o winglet pairs is carried out by varying airflow velocity in turbulent region in the test section having a constant wall heat-flux. Effects of three blockage ratios (BR=e/D= 0.1, 0.15 and 0.2) and three pitch ratios (PR=P/D= 1, 1.5 and 2) of the winglet pairs on heat transfer rates in the terms of Nusselt number (Nu) and pressure loss in the form of friction factor (f) are examined. The experimental results illustrated that the tube with winglet pair insert provides the heat transfer rate higher than the smooth tube around 1.7 to 2.6 times, depending upon operating conditions. The thermal enhancement factor for using the winglet-pair turbulator is in a range of 1.03 - 1.31. © (2014) Trans Tech Publications, Switzerland.
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Experimental study on flow friction and heat transfer in a square-duct heat exchanger with winglet turbulators
(2014-01-01)
Suwannapan, Supattarachai
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Hoonpong, Panuwat
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Promvonge, Pongjet
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Juengjaroennirachon, Sirisawat
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Pimsarn, Monsak
The paper presents an experimental study on airflow friction and heat transfer behaviors in a heat exchanger square-duct fitted with winglet turbulators. The experiments are carried out by varying the airflow rate in terms of Reynolds number from 4000 to 25,000. The winglets were mounted in tandem with three attack angles (α=30°, 45° and 60°), two winglet-pitch to duct-height ratios, (called pitch ratio, PR=P/H=1.0 and 1.5) and a single winglet-to duct-height ratio, (called blockage ratio, BR=e/H=0.2). Effects of the winglet parameters on heat transfer and pressure loss in terms of Nusselt number and friction factor are investigated. The experimental result reveals that the application of the winglets provides considerably higher heat transfer and pressure loss values than the smooth duct alone. The winglet at α=60o and PR=1 gives the maximum heat transfer and pressure loss but the one at α = 30o and PR=1.5 yields the highest thermal enhancement factor of about 1.49 at the lowest Reynolds number. © (2014) Trans Tech Publications, Switzerland.

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