Browsing by Author "Lin, Yur-Tsai"

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A novel design of pulsating heat pipe with fewer turns applicable to all orientations
(2012-10-01)
Chien, Kuo-Hsiang
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Lin, Yur-Tsai
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Chen, Yi-Rong
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Yang, Kai-Shing
;
Wang, Chi-Chuan
This study presents a novel pulsating heat pipe (PHP) concept that is functional even when PHP is with fewer turns and is operated horizontally. Two heat pipes were made of copper capillary tubes with an overall size of 122 mm x 57 mm x 5.5 mm is investigated, one had 16 parallel square channels having a uniform cross-section of 2 mm x 2 mm (uniform CLPHP), and the other had 16 alternative size of parallel square channels (non-uniform CLPHP; a cross-section 2 mm x 2 mm and a cross-section of 1 mm x 2 mm in alternating sequence). Test results showed that the performance of PHP rises with the inclination but the uniform channel CLPHP is not functional at horizontal configuration whereas the proposed non-uniform design is still functional even at horizontal arrangement. The thermal resistance for uniform PHP is relative insensitive to change of inclination when the inclination angle exceeds certain threshold value. (c) 2012 Elsevier Ltd. All rights reserved.
Effect of inclination on the convective boiling performance of a microchannel heat sink using HFE-7100
(2012-01-01)
Wang, Chi-Chuan
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Chang, Wen-Jeng
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Dai, Chia-Hsing
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Lin, Yur-Tsai
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Yang, Kai-Shing
The effect of inclination on the convective boiling heat transfer characteristics of the dielectric fluid HFE-7100 within a multiport microchannel heat sink having a hydraulic diameter of 825 pm is studied. The inclinations spans from -90 degrees (vertical downward) to 90 degrees (vertical upward), and a flow visualization is also conducted in this study. It is found that the heat transfer coefficient for the vertical upward and horizontal is comparable, and the heat transfer coefficient for 45 degrees upward considerably exceeds other configurations. On the other hand, the enhancement of heat transfer coefficient under inclined arrangement is reduced with the rise of mass flux. The results also indicate that downward arrangements always impair the heat transfer performance, and more than 50% deterioration of heat transfer coefficient is encountered for G = 100 kg m(-2) s(-1) relative to that of 45 degrees arrangement. The flow visualization confirms that the heat transfer augmentation for upward inclination is due to the rise of slug velocity. (C) 2011 Elsevier Inc. All rights reserved.
Investigation of the semi-dimple vortex generator applicable to fin-and-tube heat exchangers
(2015-09-05)
Wang, Chi-Chuan
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Chen, Kuan-Yu
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Lin, Yur-Tsai
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機械工程學系
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Department of Mechanical Engineering
The present study examines the air side performance of the fin-and-tube heat exchangers having semi-dimple vortex generator or plain fin geometry. A total of eight samples are made and tested with the corresponding fin pitch (F-P) being 1.6 mm and 2.0 mm and the number of tube row (N) are 1 and 2. The inlet air flow direction is also being tested upon the proposed semi-dimple VG. Test results indicate that the heat transfer performance of the proposed semi-dimple VG with N = 1 at a smaller fin pitch of 1.6 mm is slightly higher than that of plain fin geometry. For N = 1 with a larger fin pitch of 2.0 mm, the semi-dimple VG is about 10% higher than that of plain fin geometry. The difference in heat transfer performance amid VG and plain fin geometry becomes more pronounced with N = 2 and is especially evident when F-P = 2.0 mm due to mixing contribution. In general, the difference between plain and semi-dimple geometry becomes more conspicuous at a larger fin pitch because of the comparatively effectively swirled motion. Both geometries show a dependence on fin pitch at N = 1 but the effect is almost negligible when N is increased to 2. The inlet air flow direction casts negligible influence on the heat transfer performance of semi-dimple VG. However, the friction factors for the opposite air flow operation is lower than that of normal operation, especially in low Reynolds number region. (C) 2014 Elsevier Ltd. All rights reserved.
On the Heat Transfer Characteristics of Heat Sinks: With and Without Vortex Generators
(2010-06-01)
Yang, Kai-Shing
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Jhong, Jhih-Hao
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Lin, Yur-Tsai
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Chien, Kuo-Hsiang
;
Wang, Chi-Chuan
This paper examines the airside performance of heat sinks having fin patterns of delta, semi-circular vortex generators, plain fin and their combinations. Test results indicate that the heat transfer performance is strongly related to the developing and fully developed flow characteristics. The augmentations via vortex generator are relatively effective when the flow is in the developing region whereas they become quite less effective in the fully developed region. This is especially pronounced when the fin pitch is small or operated at a lower frontal velocity. Actually, the plain fin geometry outperforms most of the fin patterns at the fully developed region. This is because a close spacing prevented the formation of vortex, and the presence of interrupted surface may also suffer from the degradation by constriction of conduction path. The results suggest that the vortex generators operated at a higher frontal velocity and at a larger fin pitch are more beneficial than that of plain fin geometry. The semi-circular vortex generator possesses the highest heat transfer coefficients and pressure drops at developing region, suggesting the mechanism of blockage of conduction path cannot be overlooked. The performance of dense or loose vortex generator is moderate either in a developing or fully developed region. In association with the VG-1 criteria (same pumping power and same heat transfer capacity), the asymmetric design (VG+plain) reveals the best results. The design could reduce 31.1% required heat dissipation area at a frontal velocity of 5 m/s within a developing region. Yet, it is still applicable in a fully developed region with an area reduction of 1.8-11.5% at a frontal velocity 3-5 m/s.