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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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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 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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Thermal performance in circular tube with Co/counter-twisted tapes
(2014-01-01)
Chokphoemphun, Suriya
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Hinthao, Chayodom
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Eiamsa-Ard, Smith
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Promvonge, Pongjet
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Thianpong, Chinaruk
Thiswork presents an experimental study on enhanced heat transfer and pressure loss characteristics in a tube having a uniform heat-fluxed wall by using small double and triple co- and counter-twisted tapes at two twist ratios, y/w=4 and 4.5. The investigation has been conducted for Reynolds number from 5300-20,000. The experimental results of the heat transfer and pressure drop are proposed in terms of Nusselt number and friction factor, respectively.The experimental results reveal thatthe maximum TEF for the triple counter-twisted tapesat smaller twist ratio isabout 1.26. © (2014) Trans Tech Publications, Switzerland.
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Numerical heat transfer investigation in solar air heater channel with Wavy-Baffles
(2014-01-01)
Promvonge, Pongjet
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Noothong, Watcharin
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Thianpong, Chinaruk
A numerical study is conducted to investigate the turbulent periodic flow and heat transfer characteristics in a channel fitted with sinusoidal wavy-baffles placed on upper and lower walls. The finite volume method is introduced and implemented with the SIMPLE algorithm. The flow structure, friction factor and heat transfer characteristics for different wavy-baffle configurations are evaluated. According to numerical result, the maximum thermal performance is found to be 1.22–1.66 times to smooth channel corresponding to the baffle a/H=0.75 and b/H=0.10. Consequently, the application of wavy-baffles can be utilized effectively to enhance the thermal performance of solar air heater.
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Heat transfer augmentation in a helical-ribbed tube with double twisted tape inserts
(2012-08-01)
Promvonge, Pongjet
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Pethkool, Somsak
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Pimsarn, Monsak
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Thianpong, Chinaruk
Turbulent convective heat transfer characteristics in a helical-ribbed tube fitted with twin twisted tapes have been investigated experimentally. The experiment was carried out in a double tube heat exchanger using the helical-ribbed tube having a single rib-height to tube-diameter ratio, e/D <inf>H</inf>=0.06 and rib-pitch to diameter ratio, P/D <inf>H</inf>=0.27 as the tested section. The insertion of the double twisted tapes with twist ratio, Y, in the range of 2.17 to 9.39 is to create vortex flows inside the tube. The inserted ribbed tube is arranged in similar directions of the helical swirl of the twisted tape and the helical rib motion of the tube (called co-swirl). Effects of the co-swirl motion of the ribbed tube and the double twisted tapes with various twist ratios on heat transfer and friction characteristics are examined. The results obtained from the ribbed tube and the twin twisted tape insert are compared with those from the smooth tube and the ribbed tube acting alone. The experimental results reveal that the co-swirling inserted tube performs much better than the ribbed/smooth tube alone at a similar operating condition. The co-swirl tube at Y≈8 yields the highest thermal performance at lower Reynolds number (Re). In addition, the correlations of Nusselt number and friction factor as functions of Re, Pr and Y are also proposed. © 2012 Elsevier Ltd.

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