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Enhanced thermal effectiveness of square duct with V-type double-baffles: Numerical study
(2024-09-01)
Promvonge, Pongjet
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Sripattanapipat, Somchai
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Thianpong, Chinaruk
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Skullong, Sompol
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Promthaisong, Pitak
The article puts forward three-dimensional computational research on heat transmission augmentation within a square channel containing 45o V-type double-baffles positioned on the lower and top parts at regular intervals in the turbulence zone for Reynolds numbers (Re) that vary from 3000 to 20,000. The primary goal of this research is to increase the thermal effectiveness and relative Nusselt number (Nu/Nu<inf>0</inf>), in order to conserve energy and reduce the size of the heating or cooling system. The simulations utilize a finite volume approach in common with the SIMPLE algorithm, whereas the turbulent model used is the realizable k–ε. The baffles are designed to be separated vertically for reducing pressure loss. Both single V-baffles and double V-baffles have four relative pitches (PR = 0.4, 0.5, 0.6, and 1.0) and height/blockage ratios (BR = 0.05, 0.1, 0.15, and 0.2), with a fixed attack angle (α) of 45o. The computational findings show that both V-baffles are capable of producing the primary vortices, but only the double V-baffles have the ability to provide the impinging streams onto the wall, cooling the region behind the baffles. This suggests that the double V-baffles not only boost heat transmission but also reduce frictional loss. When compared to a single V-baffle, the double ones enhance heat transfer by an average of 1.04–9.94% while decreasing frictional loss by an average of 9.88–31.73%. The thermal effectiveness factor (TEF) of the double V-baffles ranges from 1.03 to 3.21, and its peak value of around 3.21 is for PR = 0.4, BR = 0.05, at lower Re.
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Thermal effectiveness enhancement in heat exchange tube using louver-punched V-baffles
(2024-06-15)
Promvonge, Pongjet
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Promthaisong, Pitak
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Skullong, Sompol
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Nakhchi, Mahdi Erfanian
An efficient technique for reducing frictional loss by punching holes on the surface of vortex generators has been extensively researched, particularly in the form of louver-punched holes. This article describes an experimental and numerical examination of thermal effectiveness in a heat exchange tube with louvered baffle vortex generators (LBVG). As air was directed to the LBVG-inserted tube with a consistent heat flux, the flow was measured in a turbulent regime. The LBVGs were set at 30° attack angle (α) and mounted at regular intervals on a two-sided flat tape with one relative baffle height (b/D = R<inf>B</inf> = 0.25) and pitch (P/D= R<inf>P</inf> = 1) at the first step. The baffles had five different louver angles (θ = 0 ˗ 90°) and three different relative louver sizes (L<inf>R</inf>= e/b = 0.4, 0.56, and 0.72). The Nusselt number ratio (Nu<inf>R</inf>), friction factor ratio (f<inf>R</inf>), and thermal effectiveness factor (TEF) were utilized to quantify the performance of LBVGs. The findings showed that LBVGs had much lower f<inf>R</inf> values than solid baffles (without holes), whereas Nu<inf>R</inf> values decreased slightly. When θ and L<inf>R</inf> were reduced, the f<inf>R</inf> and Nu<inf>R</inf> for LBVGs increased until they resembled those for solid baffles. Through numerical simulations using the realizable k-ε turbulent model based on the finite volume method, the flow and temperature fields of various cases were generated; their results were verified via analysis of the fluid flow patterns. The computational findings revealed that the jet flow from the louver hole could boost heat transfer, and TEF of LBVGs varied depending on the placement of the hole. According to the computations, the optimal TEF at R<inf>P</inf> = 0.75, L<inf>R</inf> = 0.4, and θ<inf>1</inf> = 20° is roughly 2.64, and the hole should be placed toward the baffle ends rather than in the middle.
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Heat transfer analysis in a tube contained with louver-punched triangular baffles
(2024-06-01)
Jayranaiwachira, Nuthvipa
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Promvonge, Pongjet
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Promthaisong, Pitak
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Nakhchi, Mahdi Erfanian
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Skullong, Sompol
The present research assesses the thermal effectiveness of a heat exchange tube incorporating louver-punched triangular baffle (LPTB) vortex generators under turbulent conditions. For Reynolds numbers between 4760 and 29,270, the heat transfer and flow behaviors in the consistent heat-fluxed tube equipped with LPTBs were studied numerically and experimentally. A single baffle height/blockage ratio (b/D = B<inf>R</inf> = 0.25) and relative baffle pitch (P/D = P<inf>R</inf> = 1) were used for both baffle attack angles, (α) 30° and 45°, along with three louver size ratios (e/b = L<inf>R</inf> = 0.24–0.56) as well as five louver angles (θ = 0°, 20°, 30°, 45°, 60°, and 90°). The results show that as the L<inf>R</inf> and θ values decrease, the Nusselt number (Nu) and friction factor (f) of the LPTB rise owing to the improved fluid mixing process generated by streamwise vortices with stronger turbulence kinetic energy. The LPTB with L<inf>R</inf> = 0 and θ = 0° provides the greatest f and Nu of about 22.18 and 5.1 times, respectively, although the one with L<inf>R</inf> = 0.24 and θ = 45° has the largest TEF of about 2.39 and 2.5 for the α = 30° and 45° LPTBs, respectively. Furthermore, an examination into the thermal and flow patterns was conducted through a three-dimensional computation; the validation of the numerical and experimental data yielded satisfactory results. Using measured data, the f and Nu correlations of the α = 30° and 45° LPTBs were additionally established.
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Heat transfer distribution and flow characteristics in a channel with perforated-baffles
(2022-11-01)
Eiamsa-ard, Smith
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Sripattanapipat, Somchai
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Saysroy, Anucha
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Promvonge, Pongjet
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Maruyama, Naoki
The current paper reports the prediction of heat transfer performance of a channel with a modified perforated-baffle in a square wings (SW-PB) form. Numerical results include flow/temperature field, local heat transfer distribution, and thermal performance of a channel installed with the transverse solid baffle (TB), perforated-baffle (PB), and perforated-baffle with square wings (SW-PB). The simulation results demonstrated that TB brought a large recirculation flow, PB induced small recirculation and SW-PB produced several impinging jets as well as recirculation flows. Heat transfer rates given by PB were lower than those provided by TB and SW-PB by around 6.8% and 7.3%, respectively which were accompanied by lower friction losses by about 11.8% and 3.6%, respectively. Although, SW-PB gave higher heat transfer, the assessment of thermal performance factor (TPF) showed that the benefit from lower friction losses was more important. Under the same pumping power, TPFs assisted by SW-PB were higher than that assisted by PB and TB by 6.0% and 3.3%, respectively. The highest TPF of 1.2 was captured by SW-PB at Re = 9,000.
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Thermal characterization of turbulent tube flows over diamond-shaped elements in tandem
(2010-06-01)
Eiamsa-ard, Smith
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Promvonge, Pongjet
Experiments have been conducted to investigate the heat transfer and friction factor characteristics of the fully developed turbulent airflow through a uniform heat flux tube fitted with diamond-shaped turbulators in tandem arrangements. In the experiments, strong turbulence and recirculation flow is expected by using tandem diamond-shaped turbulators (D-shape turbulator) connected to each other by a small rod and placed inside the test tube. The parameters for this study are consisted of Reynolds number (Re) from 3500 to 16,500, the included cone angle (θ = 15°, 30° and 45°), and the tail length ratio (TR = l<inf>t</inf>/l<inf>h</inf> = 1.0, 1.5 and 2.0) defined as the ratio of the tail length (l<inf>t</inf>) to the head length of turbulator (l<inf>h</inf>). The variation of Nusselt number and friction factor with Reynolds number under the effect of those parameters are determined and presented. The experimental result reveals that the heat transfer rate increases with increasing Reynolds number and the included cone angle (θ) but decreases with the rise of the tail length ratio (TR). This is because of the mixing of the fluid in the boundary layer thereby enhancing the convective heat transfer and increasing pressure loss. For the tube with the turbulator of θ = 45°, the heat transfer enhancement is found to be 67%, 57% and 46% for tail length ratio, TR = 1.0, 1.5 and 2.0, respectively. Correlations of the Nusselt number (Nu) and friction factor (f) are developed for the evaluation of interactive effects of using the turbulators on the heat transfer and pressure loss. The good agreement between the experimental and the correlated results is obtained within 5-7% deviation. In addition, the heat transfer enhancement efficiency determined under constant pumping power is also provided. © 2009 Elsevier Masson SAS. All rights reserved.
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Performance assessment in a heat exchanger tube with alternate clockwise and counter-clockwise twisted-tape inserts
(2010-03-01)
Eiamsa-ard, Smith
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Promvonge, Pongjet
The article presents an experimental study of turbulent heat transfer and flow friction characteristics in a circular tube equipped with two types of twisted tapes: (1) typical twisted tapes and (2) alternate clockwise and counterclockwise twisted tapes (C-CC twisted tapes). Nine different C-CC twisted tapes are tested in the current work; they included the tapes with three twist ratios, y/w = 3.0, 4.0 and 5.0, each with three twist angles, θ = 30o, 60o and 90o. The experiments have been performed over a Reynolds number range of 3000-27,000 under uniform heat flux conditions, using water as working fluid. The obtained results reveal that the C-CC twisted-tapes provide higher heat transfer rate, friction factor and heat transfer enhancement index than the typical twisted-tapes at similar operating conditions. The results also show that the heat transfer rate of the C-CC tapes increases with the decrease of twist ratio and the increase of twist angle values. Depending on Reynolds number, twist ratio and twist angle values, the mean Nusselt numbers in the tube fitted with the C-CC twisted tapes are higher than those with the typical ones and the plain tube around 12.8-41.9% and 27.3-90.5%, respectively. The maximum heat transfer enhancement indexes of the C-CC twisted tapes with θ = 90o for y/w = 3.0, 4.0 and 5.0, are 1.4, 1.34 and 1.3, respectively. In addition, correlations of the Nusselt number and the friction factor for using the C-CC twisted tapes are also determined. Both predicted Nusselt number and friction factor are within ±15% and ±15% deviation compared to the experimental data. © 2009 Elsevier Ltd. All rights reserved.
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Thermal characteristics of turbulent rib-grooved channel flows
(2009-08-01)
Eiamsa-ard, Smith
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Promvonge, Pongjet
Experimental work has been performed to examine the combined effects of rib-grooved turbulators on the turbulent forced convection heat transfer and friction characteristics in a rectangular duct under a uniform heat flux boundary condition. In the experiments, three types of rib-groove arrangements: rectangular-rib and triangular-groove (RR-TG), triangular-rib and rectangular-groove (TR-RG) and triangular-rib with triangular-groove (TR-TG), were examined. Measurements were carried out for the duct of one aspect ratio, AR = W/H = 20 and duct height, H = 9 mm with rib height, e = 3 mm at three pitch ratios, PR = P/e = 6.6, 10 and 13.3. Experiments were conducted for the Reynolds number range of 3000 to 10,000. Influences of rib-groove arrangements on the Nusselt number and friction factor have been discussed and compared with smooth duct results under similar test conditions. Isothermal friction factors were also taken and presented. The obtained results of the smooth duct are in good agreement with the previous studies found in the literature. Experimental results also show that the duct with RR-TG arrangement provides maximum heat transfer rate and friction factor than others. On the other hand, the thermal enhancement index obtained at constant pumping power reveals that the TR-TG provides the highest values for all pitch ratios studied. Finally, correlations for the heat transfer (Nu), friction factor (f) and the enhancement index (η) have been developed as a function of pitch ratio (PR) and Reynolds number (Re). © 2009 Elsevier Ltd. All rights reserved.
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Turbulent convection in round tube equipped with propeller type swirl generators
(2009-04-01)
Eiamsa-ard, Smith
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Rattanawong, Sarawut
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Promvonge, Pongjet
This article is aimed at studying the heat transfer, friction loss and enhancement efficiency behaviors in a heat exchanger tube equipped with propeller type swirl generators at several pitch ratios (PR). The investigation is performed for the Reynolds number ranging from 4000 to 21,000 under a uniform heat flux condition. The experiments are also undertaken for several blade numbers of the propeller (N = 4, 6, and 8 blades) and for different blade angles (θ = 30°, 45°, and 60°). The influences of using the propeller rotating freely, on heat transfer enhancement, pressure loss, and enhancement efficiency, are reported. In the experiments, the swirl generator is used to create a decaying swirl in the tube flow. Average Nusselt numbers are determined and also compared with those obtained from other similar cases. The experimental results indicate that the tube with the propeller inserts provides considerable improvement of the heat transfer rate over the plain tube around 2.07 to 2.18 times for PR = 5, blade angles θ = 60° and N = 8. The use of the propeller leads to maximum enhancement efficiency up to 1.2. Thus, because of strong swirl or rotating flow, the propellers and their blade numbers become influential upon the heat transfer enhancement. The increase in friction factor from using the propeller is found to be 3-18 times over the plain tube. Correlations for Nusselt number (Nu) and friction factor (f) for the inserted tube are provided and the performance evaluation criterion to access the real benefits in using the swirl generators of the enhanced tube is also determined. © 2009 Elsevier Ltd. All rights reserved.
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Thermal performance in circular tube fitted with coiled square wires
(2008-05-01)
Promvonge, Pongjet
The effects of wires with square cross section forming a coil used as a turbulator on the heat transfer and turbulent flow friction characteristics in a uniform heat flux, circular tube are experimentally investigated in the present work. The experiments are performed for flows with Reynolds numbers ranging from 5000 to 25,000. Two different spring coiled wire pitches are introduced. The results are also compared with those obtained from using a typical coiled circular wire, apart from the smooth tube. The experimental results reveal that the use of coiled square wire turbulators leads to a considerable increase in heat transfer and friction loss over those of a smooth wall tube. The Nusselt number increases with the rise of Reynolds number and the reduction of pitch for both circular and square wire coils. The coiled square wire provides higher heat transfer than the circular one under the same conditions. Also, performance evaluation criteria to assess the real benefits in using both coil wires of the enhanced tube are determined. © 2007 Elsevier Ltd. All rights reserved.
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Heat transfer augmentation in a circular tube using V-nozzle turbulator inserts and snail entry
(2007-10-01)
Promvonge, Pongjet
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Eiamsa-ard, Smith
Influences of V-nozzle turbulator inserts in conjunction with a snail entry on heat transfer and friction loss characteristics in a circular tube are experimentally investigated in this paper. In the present work, a set of converging-diverging nozzles like a venturi structure (referred to as V-nozzle) used as a turbulator/reverse-flow generator is placed inside the test tube through which air as the test fluid is passed. Also, the snail is mounted at the tube entrance to create a decaying swirl flow. The effects of the snail entry and insertion of V-nozzles with three different pitch ratios, PR = 2.0, 4.0, and 7.0 on heat transfer rate in the tube are examined for the Reynolds number ranging from 8000 to 18,000. The experimental results are displayed in terms of Nusselt number (Nu) and friction factor (f) as a function of Reynolds number (Re). The values of Nusselt number and friction factor for utilizing both the V-nozzle and the snail entry are found to be considerably higher than that for using the V-nozzle alone or the plain tube. The use of PR = 2.0 leads to higher Nusselt number and friction factor values than that of PR = 4.0 or 7.0. To assess the real benefits in using the turbulator and the swirl generator of the enhanced tube, empirical correlations in terms of Re and PR for Nusselt number, friction factor and performance evaluation criteria are also determined. © 2007 Elsevier Inc. All rights reserved.

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