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Investigation of turbulent thermal-hydraulic behaviors of a heat exchanger tube with U-cut twisted-tape
(2025-03-01)
Wongcharee, K.
;
Chuwattanakul, V.
;
Chamoli, S.
;
Maruyama, N.
;
Hirota, M.
This study examines the influences of U-cut twisted tapes (U-TTs) on thermal-hydraulic behaviors in a circular tube with uniform heat flux. The geometric parameters studied include six U-cut ratios (s/t = 0.5, 1.0, 1.5, 2.0, 2.5, and 3.0) and two twist ratios (y/w = 3.5 and 4.0). Experimental results revealed that their U-cut ratios highly influenced heat transfer enhancement. U-TTs with U-cut ratios (s/t) of 0.5, 1.0, 1.5, and 2.0 achieved higher Nusselt numbers than conventional twisted tapes (TTs). In contrast, U-TTs with larger U-cut ratios (s/t = 2.5 and 3.0) showed reduced Nusselt numbers. However, friction losses with all U-TTs were consistently higher than those with TTs. Due to their excellent heat transfer enhancement, U-TTs with s/t ratios of 0.5 and 1.0 exhibited significantly higher thermal performance factors (TPF) than conventional TTs. The highest TPF, 1.28, was achieved by U-TTs with an s/t ratio of 0.5 and a y/w of 3.5 at a Reynolds number of 6000.
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Influence of CuO/water nanofluid concentration and swirling flow on jet impingement cooling
(2017-11-01)
Wongcharee, K.
;
Chuwattanakul, V.
;
Eiamsa-ard, S.
CuO/water nanofluids were applied in swirling impinging jets for heat transfer enhancement. Swirling flow was induced by twisted tape inserts with twist ratios (y/w) of 1.43, 2.86 and 4.28. Impinging jets were injected at three different ratios of jet-to-plate spacing to nozzle diameter (H/d) of 2, 3 and 4. Nanofluids with CuO concentrations of 2.0%, 3.0% and 4.0% by volume were comparatively tested with water (a base fluid) for Reynolds numbers ranging from 1600 to 9400. Experimental results reveal that the nanofluids with concentrations of 2.0 and 3.0% by volume yield higher Nusselt numbers than the base fluid while the one with concentration of 4.0% shows opposite result. At the ratio of jet-to-plate spacing/nozzle diameter (H/d) of 2, Nusselt number slightly increases with decreasing twist ratio (y/w). However, at the ratios of jet-to-plate spacing/nozzle diameter (H/d) of 3 and 4, Nusselt number increases with increasing twist ratio. Over the studied range, the optimum condition is found at H/d = 2, y/w = 1.43, and nanofluid concentration of 2.0% by volume.
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Heat transfer of swirling impinging jets with TiO2-water nanofluids
(2017-01-01)
Wongcharee, K.
;
Chuwattanakul, V.
;
Eiamsa-ard, S.
An experimental work has been carried out to study the heat transfer of swirling impinging jets (SIJs) with TiO<inf>2</inf>-water nanofluids using thermochromic liquid crystal technique. Experiments were carried out at constant jet-to-target spacing ratio (L/D) of 1.0, 2.0, 3.0 and 4.0 for Reynolds numbers from 5000 to 20,000 by using nanofluids with TiO<inf>2</inf>concentrations of 0.5%, 1.0%, 1.5%, 2.0% and 2.5% by volume, twisted tapes with twist ratios (y/W) of 4.0, 5.0, 6.0 and 7.0. Conventional impinging jets (CIJs) and swirling impinging jets (SIJs) with pure water were also tested, for comparison. At similar operation conditions, swirling impinging jets (SIJs) offer superior heat transfer to conventional impinging jets. It is also found that the nanofluids with concentrations of 0.5%, 1.0%, 1.5% and 2.0% by volume give higher Nusselt numbers than the base fluid (water) while the one with concentration of 2.5% shows opposite result. Over the studied range, the optimum condition where the maximum Nusselt number is achieved at TiO<inf>2</inf>-water nanofluids with concentration of 2.0% by volume and y/W = 6.0.
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Thermohydraulic investigation of turbulent flow through a round tube equipped with twisted tapes consisting of centre wings and alternate-axes
(2010-11-01)
Eiamsa-ard, S.
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Wongcharee, K.
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Eiamsa-ard, P.
;
Thianpong, C.
The effects of the twisted tapes consisting of centre wings and alternate-axes (WT-A) on thermohydraulic properties in a round tube, were investigated. The effects of other three types of twisted tapes including: (1) the twisted tape with wings alone (WT), (2) the twisted tape with alternate axes alone (T-A), and (3) the typical twisted tape (TT), were also studied for comparison. All twisted tapes used were twisted at constant twist length (y) of 57. mm, corresponding to a constant twist ratio (y/. W) of 3.0. The wings were generated along the centre line of the tape with three different angles of attack, (β= 43°, 53° and 74°). Test runs were conducted using water as a testing fluid with Reynolds number range between 5200 and 22,000. Under the similar condition, the heat transfer rate in the tube fitted with the WT-A was consistently higher than those in the tube equipped the WT, T-A and plain tube. It is also found that the heat transfer rate increased with increasing angle of attack. Over the range studied, the use of WT-A at β= 74° was found to be the most effective for heat transfer enhancement, giving thermal performance factor of up to 1.4. Mean values of Nusselt number (Nu), friction factor (f), thermal performance factor (η) provided by the WT-A (at β= 74°) were respectively, 17.7%, 30.6% and 7.8% higher than those in the tube with WT (at β= 74°), 20.8%, 53% and 4.9% higher than those in the tube with T-A, and 62%, 123% and 24% higher than those in the tube with TT. The superior performance of the WT-A over those of the other tapes could be attributed to the combined effects of the following actions: (1) a common swirling flow by the twisted tape (2) a vortex generated by the wing (3) a strong collision of the recombined streams behind each alternate point. For a better understanding on flow phenomena, flow-visualization by smoke wire technique is also presented. In addition, the experimental correlations of Nusselt number, friction factor and thermal performance factor were also developed. © 2010 Elsevier Inc.
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Turbulent heat transfer through a heat exchanger with porous twisted tape inserts
(2009-01-01)
Eiamsa-Ard, S.
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Wongcharee, K.
;
Rattanawong, S.
;
Eiamsa-Ard, P.
;
Pimsarn, M.
In this present work, the influences of the porous twisted tape (PT) on the heat transfer and the pressure loss are studied experimentally. The comparative experiments are conducted in the tube fitted with the PT or typical twisted tape (TT) at different twist ratios, y/w = 4.0 and 5.0, in the Reynolds number ranging from 4800 to 16,000 under uniform heat flux conditions. In the experiments, the PT inserts generate swirls that modify the near wall velocity profile resulted in improvement of the heat transfer rate. The experimental results reveal that the heat transfer rates increase with decreasing twist ratio (y/w) for all twisted tapes used in the experiments. The heat transfer rates increase up to 71% with the help of the PT. The increases in average Nusselt numbers of using PT and TT are found to be 48% and 22%, respectively, over those of the corresponding plain tube. However, PT causes a considerable increase in friction factor. The mean increases of friction factors for PT and TT are respectively, about 3.14 and 2.45 times in comparison with that for the plain tube. Mean friction factor and Nusselt number for PT, are respectively 28% and 21% higher than those for TT. In addition, the empirical correlations of the Nusselt number and friction factor are also reported.

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