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Heat transfer mechanism and thermal performance of a channel with square-wing perforated transverse baffles installed: effect of square-wing location
(2023-05-01)
Eiamsa-Ard, Smith
;
Phila, Arnut
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Pimsarn, Monsak
;
Maruyama, Naoki
;
Hirota, Masafumi
The aim of this study is to report the influence of wing position (h/e) of perforated transverse baffles with square-wings (SW-PBs) on heat transfer rate and pressure drop characteristics in a channel. The channel has a cross-sectional dimension of 15 cm × 4 cm and a length of 60 cm. Two types of baffles: Solid transverse baffles and square-wing perforated transverse baffles, are comparatively tested. The baffle pitch ratio (p/e) is set to 5.0 and remains constant throughout all experiments which encompass Reynolds numbers (Re) of 6000, 9000, 12,000, 15,000, 18,000, 21,000, and 24,000. Square-wings are introduced at four different locations, h/e = 0.92 (highest wing location), 0.83, 0.75, and 0.67 (lowest wing location). The maximum heat transfer rates achieved in channels with SW-PBs at h/e = 0.92, 0.83, 0.75, and 0.67 are 148%, 157%, 166%, and 180% above that of a plain channel, while pressure losses increase by 9.51–10.69, 9.56–10.79, 9.59–10.86, and 9.64–10.99 times, respectively. Experimental results show that square-wings create multiple impinging jet flows and Nusselt number peaks appear adjacent to the rear of the perforated transverse baffles. When compared to solid transverse baffles, SW-PBs cause lower pressure losses and yield higher thermal performance.
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Effect of geometrical parameters on turbulent flow and heat transfer behaviors in triple-start corrugated tubes
(2018-01-01)
Promthaisong, Pitak
;
Jedsadaratanachai, Withada
;
Eiamsa-Ard, Smith
Computational results of flow structure, pressure loss and heat transfer characteristics in triple-start corrugated tubes are reported. The influences of the depth ratio (DR = 0.02, 0.04, 0.06, 0.08, 0.1, 0.12, 0.14 and 0.16) and pitch ratio (PR = 0.5, 0.65, 0.75, 1.0, 1.5 and 2.0) were investigated in turbulent flow regime, Re = 5000 to 20,000. The computational results indicated that the triple-start corrugated tubes generate main swirl flow and helical swirl flow which helps to reduce the thermal boundary layer thickness and enhance the heat transfer rate. The flow and heat transfer become under fully developed periodic condition around x/D = 6.0. The friction factor monotonically increases with the rise of DR values and decrease PR values while maximum heat transfer rate is found at DR = 0.08 and PR = 0.75. Nusselt numbers and friction factors of triple-start corrugated tubes in the investigated range are found to be 0.8 to 2.31 and 1.0 to 17.14 times over those of the straight circular smooth tube, respectively. For the range studied, the triple-start corrugated tube with DR = 0.06 and PR = 0.75 offers the maximum thermal enhancement factor of 1.21 at Re = 5000.
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Thermal performance evaluation of micro-fin tube with twisted tape inserts
(2015-01-01)
Eiamsa-Ard, Smith
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Kunlabud, Suttisak
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Wongcharee, Khwanchit
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Pimsarn, Monsak
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Eiamsa-Ard, Petpices
The heat transfer coefficient and pressure drop characteristics of turbulent flow through micro-fin tubes fitted with twisted tape in co/counter-arrangement have been studied. In the experiments, water as the tested fluid is passed in a Reynolds number range of 7800 to 17,650. The results reveal that, the Nusselt numbers in the system with a micro-fin tube and twisted tape are considerably higher than those in the system without tape. Evidently, the tape with the smaller twist ratio gives higher heat transfer rate, friction factor as well as thermal performance factor than the one with larger twist ratio as a result of a larger contact surface area, and stronger turbulence intensity and thus better fluid mixing which leads to a thinner thermal boundary layer. The result reveals that for using the micro-fin tube with twisted tape, the increases in the mean Nusselt number and friction factor are, respectively, up to 181% and 3.86 times of the plain tube and the maximum thermal performance factor is 1.52. It is also obvious that the heat transfer and friction factor obtained from the micro-fin tube with twisted tape in counter-arrangement is higher than that from the micro-fin tube with twisted tape in co-arrangement.
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Heat transfer enhancement of turbulent flow through dimpled tubes fitted with twisted tapes
(2015-01-01)
Eiamsa-Ard, Smith
;
Wongcharee, Khwanchit
;
Eiamsa-Ard, Petpices
;
Chuwattanakul, Varesa
Heat transfer, pressure drop and thermal performance characteristics in ellipsoidal dimpled tubes fitted with twisted-tape swirl generators have been studied experimentally. Ellipsoidal dimpled surfaces function as the turbulence promoter near the tube wall while twisted-tapes act as the swirling flow generators. The experiments were performed by using twisted tapes with different twist ratios (y/W = 3.0, 4.0 and 5.0) and water as the working fluid for Reynolds numbers between 5000 and 15,000. The experimental results of the dimpled tubes equipped with twisted-tape were compared with those of the dimpled and plain tubes without twisted tape. Evidently, the dimpled tubes fitted with twisted-tapes consistently yield higher Nusselt numbers and friction factors than the dimpled and plain tubes without twisted tape. It is also found that the average Nusselt numbers of the dimpled tubes equipped with twisted-tapes at y/W = 3.0, 4.0 and 5.0 are higher than those of the dimpled tube alone up to 40.7%, 32% and 26.7%, respectively which correspond to the higher thermal performance factors up to 10.8%, 6.7% and 3.6%, respectively. Depending upon Reynolds number, the dimpled tube with twisted-tape at the smallest twist ratio, y/W = 3.0, give higher thermal performance factors than those at y/W = 4.0 and 5.0 by around 3.9% and 6.7%.
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Heat transfer enhancement by multiple twisted tape inserts and TiO 2/water nanofluid
(2014-09-05)
Eiamsa-Ard, Smith
;
Kiatkittipong, Kunlanan
The aim of this present work is to enhance thermal performance characteristics in a heat exchanger tube by studying: (i) multiple twisted tapes in different arrangements; (ii) TiO<inf>2</inf> nanoparticles with different concentrations as the working fluid. The tube inserted the multiple twisted tapes showed superior thermal performance factor when compared with plain tube or the tube inserted a single twisted tape, due to continuous multiple swirling flow and multi-longitudinal vortices flow along the test tube. The higher number of twisted tape inserts led to an enhancement of thermal performance that resulted from increasing contact surface area, residence time, swirl intensity and fluid mixing with multi-longitudinal vortices flow. Moreover, arrangement of twisted tapes in counter current was superior energy saving devices for the practical use, particularly at low Reynolds number. This was especially the case for quadruple counter tapes in the cross directions (CC-QTs) where heat transfer enhancement with relatively low friction loss penalty was deserved. The use of CC-QTs led to the highest thermal performance factor up to 1.45. Using water with TiO<inf>2</inf> nanoparticle as a working fluid yielded a higher thermal performance than using pure water. The tube inserted CC-QTs with TiO<inf>2</inf>/water nanofluid at concentration of 0.21% by volume provided the highest thermal performance factor 1.59, where heat transfer rate and friction factor increased to 3.52 times and 11.7 times of those in the plain tube with water as the working fluid. © 2014 Elsevier Ltd. All rights reserved.

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