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Thermal performance enhancement in solar air heater channel with periodically V-shaped baffles
(2012-12-01)
Khanoknaiyakarn, C.
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Kwankaomeng, S.
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Promvonge, P.
The research paper presents a study on thermal performance enhancement in a rectangular channel heat exchanger mounted with periodically V-shaped baffles. The channel has an aspect ratio (width to height ratio), AR=10 and height, H=30 mm while baffle characteristics are the baffle to channel height ratio, e/H=0.2, 0.3 and 0.4; the baffle pitch to channel height ratio, PR=P/H=2 and 2.67; the attack angle (α) of 30°relative to the flow direction. The experiment has been conducted by varying air flow velocity in order to adjust Reynolds number range from 5000 to 25,000. 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 effects of the baffles on Nusselt number and friction factor have been examined. The overall performance of tested baffled channel is evaluated to obtain the degree of heat transfer enhancement and friction factor induced by baffles with respect to the smooth channel under similar flow conditions. © 2011 IEEE.
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Thermal behavior in solar air heater channel fitted with combined rib and delta-winglet
(2011-07-01)
Promvonge, P.
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Khanoknaiyakarn, C.
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Kwankaomeng, S.
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Thianpong, C.
Effects of combined ribs and delta-winglet type vortex generators (DWs) on forced convection heat transfer and friction loss behaviors for turbulent airflow through a solar air heater channel are experimentally investigated in the present work. Measurements are carried out in the rectangular channel of aspect ratio, AR=10 and height, H=30mm. The flow rate is presented in the form of Reynolds numbers based on the inlet hydraulic diameter of the channel ranging from 5000 to 22,000. The cross-section shape of the rib placed on the absorber plate to create a reverse-flow is an isosceles triangle with a single rib height, e/H=0.2 and rib pitch, P<inf>l</inf>/H=1.33. Ten pairs of the DW with its height, b/H=0.4; transverse pitch, P<inf>t</inf>/H=1 and three attack angles (α) of 60°, 45° and 30° are introduced and mounted on the lower plate entrance of the tested channel to generate longitudinal vortex flows. The experimental results show that the Nusselt number and friction factor values for combined rib and DW are found to be much higher than those for the rib/DW alone. The larger attack angle of the DW leads to higher heat transfer and friction loss than the lower one. In common with the rib, the DW pointing upstream (PU-DW) is found to give higher heat transfer rate and friction loss than the DW pointing downstream (PD-DW) at a similar operating condition. In comparison, the largest attack angle (α=60°) of the PU-DW yields the highest increase in both the Nusselt number and friction factor while the lowest attack angle of the PD-DW provides the best thermal performance. © 2011 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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Laminar periodic flow and heat transfer in square channel with 30° inclined baffles
(2010-12-06)
Kwankaomeng, S.
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Jedsadaratanachai, W.
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Promvonge, P.
A numerical investigation has been carried out to study laminar flow and heat transfer characteristics in a three-dimensional isothermal wall square-channel with 30° staggered angled-baffles. The computations are based on the finite volume method, and the SIMPLE algorithm has been implemented. The fluid flow and heat transfer characteristics are presented for Reynolds numbers based on the hydraulic diameter of the channel ranging from 100 to 1200. To generate a pair of stream wise counter-rotating vortex (P-vortex) flows through the tested channel, the baffles (like rectangular winglet) with the attack angle of 30° are mounted in tandem and staggered arrangement on both upper and lower walls of the test channel. Effects of different baffle heights at a single pitch ratio (PR=3) on heat transfer and pressure loss in the channel are studied. It is found that P-vortex flows created by the 30° baffle exist and help to induce impinging jets on a side wall and the upper and lower wall leading to drastic increase in heat transfer rate over the test channel. In addition, the increase in the baffle height results in the rise of Nusselt number and friction factor values. The computational results reveal that the optimum thermal enhancement factor of the baffle is about 2.9 at height of 0.15 times of the channel height.
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Numerical investigation of laminar heat transfer in a square channel with 45° inclined baffles
(2010-02-01)
Promvonge, P.
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Sripattanapipat, S.
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Tamna, S.
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Kwankaomeng, S.
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Thianpong, C.
A numerical investigation of laminar periodic flow and heat transfer in a three-dimensional isothermal-wall square channel fitted with 45° inclined baffles on one channel wall is carried out in the present work. The finite volume method is introduced and the SIMPLE algorithm has been implemented for all computations. The fluid flow and heat transfer characteristics are presented for Reynolds numbers ranging from 100 to 1200. The 45° baffle mounted only on the lower channel wall has a height of b and an axial pitch length (L) equal to channel height (H). Effects of flow blockage ratios, BR = b/H = 0.1-0.5, on heat transfer and pressure loss in the square channel are examined and also compared with the typical case of the transverse baffle (or 90° baffle). It is found that apart from the rise of Reynolds number, the increase in the blockage ratio with the attack angle (α) of 45° results in considerable increases in the Nusselt number and friction factor values. The use of the 45° baffle can help to generate a streamwise main vortex flow throughout the channel leading to fast and chaotic mixing of flow between the core and the wall regions. In addition, the computational results reveal that the significant increase in heat transfer rate is due to impingement jets induced by a longitudinal vortex pair (P-vortex) of flow, appearing on the upper, lower and baffle trailing end side walls. The appearance of vortex-induced impingement flows created by the baffles leads to the maximum thermal enhancement factor of about 2.2 at BR = 0.4 and Re = 1200. The enhancement factor of the 45° baffle investigated is found to be higher than that of the 90° baffle for all Reynolds numbers and baffle heights. © 2009 Elsevier Ltd. All rights reserved.

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