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Enhanced heat transfer in rectangular duct with punched winglets
(2020-03-01)
Promvonge, Pongjet
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Skullong, Sompol
Thermal performance of a heat exchanger duct with punched winglets (PWs) mounted on the upper duct wall has been examined for Reynolds number (Re) ranging from 4100 to 25,500. In the present experiment, two types of PWs: punched delta- and elliptical-winglets (P-DW and P-EW) with four punched-hole sizes were tested at a fixed attack angle, optimal relative pitch and height. Also, data of solid delta- and elliptical-winglets (DW and EW) were included for comparison. The investigation has shown that the P-DW yields higher thermal-performance enhancement factor (η) than the P-EW. Although the solid DW and EW with no punch have the highest heat transfer and friction loss, the PWs yield better η than the solid ones. For PWs, the P-DW with smaller hole size has the peak heat transfer and friction loss around 5.7 and 40 times over the smooth duct, respectively but the optimum η of 2.17 is seen for the one with a certain hole size. The PWs provide η at about 5%–8% above the solid winglets.
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Numerical Heat Transfer Study of Turbulent Tube Flow through Winglet-pairs
(2016-11-01)
Tamna, Sombat
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Sripattanapipat, Somchai
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Promvonge, Pongjet
A numerical investigation on heat transfer behaviors in a constant heat-fluxed round tube inserted with winglet vortex generators is conducted. Air as the working medium flows through the tube for Reynolds numbers (Re) between 4000 and 20,000. The effect of using the rectangular-winglet tape (RWT) on heat transfer characteristics in the tube is numerically examined. For comparison purpose, the trapezoidal-winglet tape (TWT) and delta-winglet tape (DWT) are also offered. The RWT parameters in this work include four relative winglet-to-tube heights or blockage ratios (B<inf>R</inf>=b/D= 0.1, 0.15, 0.2, and 0.25) while the TWT and DWT are only at B<inf>R</inf>= 0.2. All the winglet pairs are at a single attack angle (α= 45°) and pitch ratio (p/D=P<inf>R</inf>=4). The numerical results show that the Nusselt number (Nu) and friction factor (f) of the tube inserts are enhanced with increasing B<inf>R</inf> values. The Nu for the inserted tube is about 1.8-2.7 times above that for the smooth tube while the f is around 4.5-11 times higher. For the studied B<inf>R</inf> ranges, the highest thermal performance is 1.48 for the RWT with B<inf>R</inf>= 0.1 at lower Reynolds number.
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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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Experimental study on heat transfer in square duct with combined twisted-tape and winglet vortex generators
(2014-12-01)
Promvonge, Pongjet
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Suwannapan, Supattarachai
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Pimsarn, Monsak
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Thianpong, Chinaruk
The article presents an experimental investigation on thermal performance enhancement in a constant heat-fluxed square duct fitted with combined twisted-tape and winglet vortex generators. The experiments are carried out for the airflow rate through the tested square duct fitted with both the vortex generators for Reynolds number from 4000 to 30,000. The effect of the combined twisted tape and rectangular winglet inserts on heat transfer and pressure drop presented in terms of respective Nusselt number and friction factor is experimentally investigated. The characteristics of the combined twisted-tape and winglet include two twist ratios (Y=4 and 5), three winglet- to duct-height ratios, (R<inf>B</inf>=0.1, 0.15 and 0.2), four winglet-pitch to tape-width ratios, (R<inf>P</inf>=2, 2.5, 4 and 5) and a single attack angle of winglet, α=30°. The experimental results reveal that the Nusselt number and friction factor for the combined twisted-tape and V-winglet increase with increasing R<inf>B</inf> but decreasing R<inf>P</inf>. The inserted duct at R<inf>B</inf>=0.2, R<inf>P</inf>=2 and Y=4 provides the highest heat transfer rate and friction factor but the one at R<inf>B</inf>=0.1, R<inf>P</inf>=2 and Y=4 yields the highest thermal performance. The application of combined vortex-flow devices gives thermal performance around 17% higher than the twisted tape alone.
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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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Turbulent convection in a solar air heater channel with baffles/winglets
(2014-01-01)
Skullong, S.
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Tamna, S.
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Promvonge, P.
The paper presents a study on heat transfer, friction loss and thermal performance behaviors in a solar air heater channel fitted with baffle turbulator (BT) or triangular-winglet vortex generator (WVG) at various winglet/baffle to channel-height or blockage ratios (BR=b/H=0.1 0.15 and 0.2). The BT and the WVG were placed only on the upper wall/absorber plate of the test channel at a single axial pitch ratio (PR=P<inf>1</inf>/H=4). The investigation is performed for the Reynolds number ranging from 5400 to 23,000. The upper wall of the channel is uniformly heated as a constant heat flux while the rests are covered with thermal insulations to reduce heat loss to surroundings. The BT and the WVG were, respectively, mounted with the attack angle of 90° and 60° relative to main flow direction. The experimental results indicate that the absorber plate with the WVGs provides considerable improvement of the heat transfer rate over the smooth channel around 4.29 to 4.33 times for BR=0.2. The use of the WVG placed on the absorber plate leads to the highest heat transfer rate, friction factor and thermal performance in comparison with the BT and the smooth channel. The WVG at BR=0.2 provides the maximum thermal performance up to 1.61. Thus, because of stronger vortex flow, the WVG at largest BR becomes influential upon the heat transfer and thermal performance enhancement. © 2014 Asian Institute of Technology.
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Enhanced heat transfer in a triangular ribbed channel with longitudinal vortex generators
(2010-06-01)
Promvonge, Pongjet
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Chompookham, Teerapat
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Kwankaomeng, Sutapat
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Thianpong, Chinaruk
Effects of combined ribs and winglet type vortex generators (WVGs) on forced convection heat transfer and friction loss behaviors for turbulent airflow through a constant heat flux channel are experimentally investigated in the present work. The cross-section of the ribs placed inside the opposite channel walls to create a reverse flow is an isosceles triangle shape. Two rib arrangements, namely, in-line and staggered arrays, are introduced. Also, two pairs of the WVGs with various attack angles (α) of 60°, 45° and 30° are mounted on the test duct entrance to create a longitudinal vortex flow through the test channel. Measurements are carried out for a rectangular duct of aspect ratio, AR = 10 and height, H = 30 mm with a single rib height, e/H = 0.13 and rib pitch, P/H = 1.33. The flow rate is in terms of Reynolds numbers based on the inlet hydraulic diameter of the channel ranging from 5000 to 22,000. The experimental results show a significant effect of the presence of the rib turbulator and the WVGs on the heat transfer rate and friction loss over the smooth wall channel. The values of Nusselt number and friction factor for utilizing both the rib and the WVGs are found to be considerably higher than those for using the rib or the WVGs alone. The larger the attack angle value leads to higher heat transfer and friction loss than the lower one. The in-line rib together with the WVGs provides higher heat transfer and friction loss than the staggered one for similar operating conditions. In common with the WVGs, the in-line rib yields the highest increase in both the Nusselt number and the friction factor but the rib with staggered array shows better thermal performance than the others. © 2010 Elsevier Ltd. All rights reserved.
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Heat transfer augmentation in a wedge-ribbed channel using winglet vortex generators
(2010-02-01)
Chompookham, Teerapat
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Thianpong, Chinaruk
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Kwankaomeng, Sutapat
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Promvonge, Pongjet
Experimental investigations have been carried out to study the effect of combined wedge ribs and winglet type vortex generators (WVGs) on heat transfer and friction loss behaviors for turbulent airflow through a constant heat flux channel. To create a reverse flow in the channel, two types of wedge (right-triangle) ribs are introduced: wedge ribs pointing downstream and pointing upstream. The arrangements of both rib types placed inside the opposite channel walls are in-line and staggered arrays. To generate longitudinal vortex flows through the tested section, two pairs of the WVGs with the attack angle of 60° are mounted on the test channel entrance. The test channel has an aspect ratio, AR = 10 and height, H = 30 mm with a rib height, e/H = 0.2 and rib pitch, P/H = 1.33. The flow rate in terms of Reynolds numbers is based on the inlet hydraulic diameter of the channel ranging from 5000 to 22,000. The presence of the combined ribs and the WVGs shows the significant increase in heat transfer rate and friction loss over the smooth channel. The Nusselt number and friction factor values obtained from combined the ribs and the WVGs are found to be much higher than those from the ribs/WVGs alone. In conjunction with the WVGs, the in-line wedge pointing downstream provides the highest increase in both the heat transfer rate and the friction factor while the staggered wedge pointing upstream yields the best thermal performance. © 2009 Elsevier Ltd. All rights reserved.
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Thermal enhancement in a solar air heater channel using rectangular winglet vortex generators
(2010-01-01)
Depaiwa, Nattawoot
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Chompookham, Teerapat
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Promvonge, Pongjet
The forced convection heat transfer and friction loss behaviors for turbulent airflow through a constant heat flux channel solar air heater with rectangular winglet vortex generator (WVG) are experimentally investigated in this work. The rectangular winglet pairs are considered with two different arrangements by pointing upstream (PU) and pointing downstream (PD) of the flow. Ten pairs of the WVGs with various attack angles (a) of 60°, 45° and 30° are mounted on the test duct entrance wall to create longitudinal vortex flows over the tested channel. Measurements are carried out for the rectangular channel air heater of aspect ratio, AR = 10 and height, H = 30 mm with the WVG height, b/H = 0.4 and a transverse pitch ratio, P/H = 1. The flow rate is in terms of Reynolds numbers based on the inlet hydraulic diameter of the channel ranging from 5000 to 23,000. The experimental results show that the solar air heater channel with rectangular WVG provides significantly higher heat transfer rate and friction loss than the smooth wall channel. The use of larger attack angle value leads to higher heat transfer rate and friction loss than that of lower one. The PD-WVGs performs higher heat transfer rate and friction loss than the PU one for similar operating conditions. In comparison, the largest attack angle (α= 60°) of the PDWVGs yields the highest increase in Nusselt number and friction factor while the lowest attack angle (α = 30°) of the PU-WVGs shows the best thermal performance.

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