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Influence of triangular wavy baffles on heat and fluid flow characteristics in a channel
(2013-07-01)
Eiamsa-ard, S.
;
Pattanapipat, S.
;
Promvonge, P.
Laminar periodic flow and heat transfer in a three-dimensional channel with triangular wavy baffles (TWBs) have been numerically investigated. The baffles with three different angles of attack: 30°, 45° and 60° have been considered for Reynolds numbers ranging from 100 to 1000. For a better understanding in the heat transfer mechanisms, the pressure contour, secondary flow pattern, streamlines of impinging flow, wall streamline and iso-surface are also reported. Apparently, each wavy baffle generates two counter-rotating vortices. The 30° and 45° baffles generate vortices with comparable intensities which are considerably higher than that caused by 60° baffles. At similar conditions, the 30° and 45° baffles give comparable Nu/Nu<inf>0</inf> values which are considerably higher than that provided by the 60° baffles, but the 30° baffles cause lower f/f <inf>0</inf> than the 45° and 60° baffles. For the range determined, the maximum thermal performances achieved by using baffles with the attack angles of 30°, 45° and 60° are 2.3, 2.2, and 1.88, respectively. © 2013 The Korean Society of Mechanical Engineers and Springer-Verlag Berlin Heidelberg.
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Effect of perforated twisted-tapes with parallel wings on heat transfer enhancement in a heat exchanger tube
(2012-01-01)
Thianpong, C.
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Eiamsa-Ard, P.
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Promvonge, P.
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Eiamsa-Ard, S.
This article reports an experimental investigation on heat transfer and pressure drop characteristics of turbulent flow in a heating tube equipped with perforated twisted tapes with parallel wings (PTT) for Reynolds number between 5500 and 20500. The design of PTT involves the following concepts: (1) wings induce an extra turbulence near tube wall and thus efficiently disrupt a thermal boundary layer (2) holes existing along a core tube, diminish pressure loss within the tube. The parameters investigated were the hole diameter ratio (d/W = 0.11, 0.33 and 0.55) and wing depth ratio (w/W = 0.11, 0.22 and 0.33). A typical twisted tape was also tested for an assessment. Compared to the plain tube, the tubes with PTT and TT yielded heat transfer enhancement up to 208% and 190%, respectively. The evaluation of overall performance under the same pumping power reveal that the PTT with d/W = 0.11 and w/W = 0.33, gave the maximum thermal performance factor of 1.32, at Reynolds number of 5500. Empirical correlations of the heat transfer, friction factor and thermal performance for tubes with PTTs were also developed. In addition, the swirling/axial flow patterns of tube with PTT were visualized using dye injection technique. © 2011 Published by Elsevier Ltd.
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Turbulent heat transfer enhancement in a heat exchanger using helically corrugated tube
(2011-03-01)
Pethkool, S.
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Eiamsa-ard, S.
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Kwankaomeng, S.
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Promvonge, P.
The augmentation of convective heat transfer in a single-phase turbulent flow by using helically corrugated tubes has been experimentally investigated. Effects of pitch-to-diameter ratio (P/D<inf>H</inf>=0.18, 0.22 and 0.27) and rib-height to diameter ratio (e/D<inf>H</inf>=0.02, 0.04 and 0.06) of helically corrugated tubes on the heat transfer enhancement, isothermal friction and thermal performance factor in a concentric tube heat exchanger are examined. The experiments were conducted over a wide range of turbulent fluid flow of Reynolds number from 5500 to 60,000 by employing water as the test fluid. Experimental results show that the heat transfer and thermal performance of the corrugated tube are considerably increased compared to those of the smooth tube. The mean increase in heat transfer rate is between 123% and 232% at the test range, depending on the rib height/pitch ratios and Reynolds number while the maximum thermal performance is found to be about 2.3 for using the corrugated tube with P/D<inf>H</inf>=0.27 and e/D<inf>H</inf>=0.06 at low Reynolds number. Also, the pressure loss result reveals that the average friction factor of the corrugated tube is in a range between 1.46 and 1.93 times over the smooth tube. In addition, correlations of the Nusselt number, friction factor and thermal performance factor in terms of pitch ratio (P/D<inf>H</inf>), rib-height ratio (e/D<inf>H</inf>), Reynolds number (Re), and Prandtl number (Pr) for the corrugated tube are determined, based on the curve fitting of the experimental data. © 2010 Elsevier Ltd.
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Influence of combined non-uniform wire coil and twisted tape inserts on thermal performance characteristics
(2010-08-01)
Eiamsa-ard, S.
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Nivesrangsan, P.
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Chokphoemphun, S.
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Promvonge, P.
In this paper, heat transfer, friction factor and thermal performance behaviors in a tube equipped with the combined devices between the twisted tape (TT) and constant/periodically varying wire coil pitch ratio are experimentally investigated. The periodically varying three coil pitch ratios were arranged into two different forms: (1) D-coil (decreasing coil pitch ratio arrangement) and (2) DI-coil (decreasing/increasing coil pitch ratio arrangement) while the twisted tapes were prepared with two different twist ratios. Each device alone is also tested and the results are subjected for comparison with those from the combined devices. The experiments were conducted in a turbulent flow regime with Reynolds numbers ranging from 4600 to 20,000 using air as the test fluid. Compared to each enhancement device, the heat transfer rate is further augmented by the compound devices. Over the range investigated, the highest thermal performance factor of around 1.25 is found by using DI-coil in common with the TT at lower Reynolds number. In addition, the empirical correlations of the heat transfer (Nu) and pressure drop (f) are also presented. © 2010 Elsevier Ltd.
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Heat transfer behaviors in a tube with combined conical-ring and twisted-tape insert
(2007-08-01)
Promvonge, P.
;
Eiamsa-ard, S.
Heat transfer, friction factor and enhancement efficiency characteristics in a circular tube fitted with conical-ring turbulators and a twisted-tape swirl generator have been investigated experimentally. The heat transfer test section is heated electrically imposing axially and circumferentially constant wall heat flux boundary conditions. In the experiments, two enhancement heat transfer devices are applied. One is the conical-ring used as a turbulator and placed in the tested tube and the other is the twisted-tape swirl generator placed at the core of the conical-ring. Air as the tested fluid is passed both enhancement devices in a Reynolds number range of 6000 to 26,000. Two twisted-tapes of different twist ratios, Y = 3.75, and 7.5, are introduced in each run. The experimental results reveal that the tube fitted with the conical-ring and twisted-tape provides Nusselt number values of around 4 to 10% and enhancement efficiency of 4 to 8% higher than that with the conical-ring alone. A maximum heat transfer rate of 367% and enhancement efficiency of around 1.96 is found for using the conical-ring and the twisted-tape of Y = 3.75. For all the devices used, the enhancement efficiency tends to decrease with the rise of Reynolds number and to be nearly uniform for Reynolds number over 16,000. In addition, correlations for Nusselt number, friction factor and performance evaluation criteria to assess the real benefits in using the turbulator and swirl generator of the enhanced tube are determined. © 2007 Elsevier Ltd. All rights reserved.
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Heat transfer enhancement in a tube with combined conical-nozzle inserts and swirl generator
(2006-11-01)
Promvonge, P.
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Eiamsa-ard, S.
The enhancements of heat transfer characteristics in a uniform heat flux circular tube fitted with conical nozzles and swirl generator are experimentally investigated. In this research, the conical nozzles, assumed as a turbulator/reverse flow generator, are placed in a model pipe line through which air as working fluid is passed. Three different pitch ratios (PR) of conical-nozzle arrangements in the test tube are introduced with PR = 2.0, 4.0 and 7.0 in each run. In addition, the snail is also employed to provide swirling flow at the inlet of the test tube. It is found that each application of the conical nozzle and the snail can help to increase considerably the heat transfer rate over that of the plain tube by about 278% and 206%, respectively. The use of the conical nozzle in common with the snail leads to a maximum heat transfer rate that is up by 316%. Correlation equations for Nusselt number, friction factor and performance evaluation criteria to assess the real benefits in using the turbulators and swirl generator of the enhanced tube are determined. © 2006 Elsevier Ltd. All rights reserved.
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Experimental investigation of heat transfer and friction characteristics in a circular tube fitted with V-nozzle turbulators
(2006-05-01)
Eiamsa-ard, S.
;
Promvonge, P.
The effects of V-nozzle inserts on heat transfer and friction characteristics in a uniform heat flux tube are experimentally studied. Three different pitch ratios (PR) of V-nozzle arrangements in the test tube are introduced with PR = 2.0, 4.0, and 7.0, in each run. The results of experimental investigations of heat transfer, friction characteristic and enhancement efficiency are presented. It is found that using the V-nozzle can help to increase considerably the heat transfer rate at about 270% over the plain tube. A maximum gain of 1.19 on enhancement efficiency is obtained for the smallest pitch ratio used, PR = 2.0. This indicates that the effect of the reverse/re-circulation flows can improve the heat transfer rate in the tube. In addition, correlations from the results are presented. © 2006 Elsevier Ltd. All rights reserved.

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