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Performance Assessment of Solar Air Heater Channel with Inclined Groove Turbulators
(2025-05-19)
Koolnapadol, N.
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Promvonge, P.
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Khanoknaiyakarn, C.
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Promthaisong, P.
;
Hoonpong, P.
An experimental investigation was carried out to explore the thermal performance and frictional loss features in a solar air heater (SAH) channel that was intentionally roughened on the absorber surface using multiple inclined groove turbulators. The working fluid, air, flows into the SAH channel, which has a consistent surface heat flux for Reynolds numbers (Re) varying between 5290 and 22,600 in the current research. Thermal characteristics at a single inclination angle (a = 45°) are investigated in this research by comparing the effects of three distinct relative groove frequencies (P/H=PR=0.8, 1.2 and 1.6) and groove depth ratios (D/H=DR=0.16, 0.24 and 0.32). The findings highlight that the employ of inclined grooves results in a noticeable rise in Nusselt number (Nu) from 1.24 to 2.82 times relative to the smooth absorber plate (smooth channel), as well as a 1.88 to 7.9 times increase in friction factor (f). The Nu and f show an increasing trend when Re increases, whereas the opposite pattern occurs as DR and PR increase. At PR = 0.8 and DR = 0.32, the inclined groove roughness has the largest thermal effectiveness factor (TEF) of around 1.64. The Nu and f correlations, which are functions of inclined groove features, have also been established.
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Investigation of heat transfer enhancement by perforated helical twisted-tapes
(2014-03-01)
Nanan, K.
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Thianpong, C.
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Promvonge, P.
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Eiamsa-ard, S.
Influence of perforated helical twisted-tapes (P-HTTs) on the heat transfer, friction loss and thermal performance characteristics under a uniform heat flux condition is reported. The P-HTTs were obtained by perforating typical helical twisted-tapes (HTTs) with a prospect to reduce the friction loss of fluid flow. The experiments were conducted using P-HTTs' three different diameter ratios (d/. w) of 0.2, 0.4 and 0.6, and three different perforation pitch ratios (s/. w) of 1, 1.5 and 2. The helical pitch ratio and twist ratio were fixed at P/. D=2 and y/. w=3. Tests were performed for Reynolds number between 6000 and 20,000. The experiments using the plain tube and the tubes with HTTs were also carried out for assessment. The experimental results reveal that the use of P-HTTs leads to the reduction of friction loss as compare to that of HTT. Heat transfer, friction loss and thermal performance factor increase as d/. w decreases and s/. w increases. For the present range, the maximum thermal performance factor of 1.28 is obtained by using the P-HTT with d/. w=0.2 and s/. w=2.0 at the Reynolds number of 6000. In addition, the empirical correlations for Nusselt number, friction factor and thermal performance factor give accurate predictions within ±. 4%, ±. 6% and ±. 3%, respectively. © 2014 Elsevier Ltd.
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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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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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