Browsing by Author "Chien, Kuo-Hsiang"

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A novel design of pulsating heat pipe with fewer turns applicable to all orientations
(2012-10-01)
Chien, Kuo-Hsiang
;
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.
A novel double pipe pulsating heat pipe design to tackle inverted heat source arrangement
(2016-08-05)
Tseng, Chih-Yung
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Yang, Kai-Shing
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Chien, Kuo-Hsiang
;
Wu, Shih-Kuo
;
Wang, Chi-Chuan
Traditional pulsating heat pipe with fewer turns is functional only when the heat source is placed at the bottom while the heat sink is on top. This study proposes a novel design having alternative double-pipe tube diameter with some extra open connections of these double-pipes. By introducing extra un-balanced pressure force, capillary force and gravity force, the PHP can be easily starting up even for an opposite heat source/sink arrangement while the conventional single tube design fails to start up with this opposite arrangement. The thermal resistance of double pipe PHP can be lowered to 0.0729 W/K with an effective thermal conductivity of 12,603 W/m.K when the heat source is placed on top. Yet the thermal resistance for the proposed double pipe design is only half of the single tube design. (C) 2016 Elsevier Ltd. All rights reserved.
An experimental investigation of air cooling thermal module using various enhancements at low Reynolds number region
(2010-12-01)
Yang, Kai-Shing
;
Li, Shu-Lin
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Chen, Ing Youn
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Chien, Kuo-Hsiang
;
Hu, Robert
This study examines the airside performance of heat sinks having fin patterns of plate fin (Type I), interrupted fill geometry (Type II), dense vortex generator (Type III), and loose vortex generator (Type IV). Test results indicate that the heat transfer performance is strongly related to the arrangement of enhancements. The interrupted and dense vortex generator configurations normally contribute more pressure drop penalty than improvements of heat transfer. This is especially pronounced when operated at a lower frontal velocity. Actually the plain fin geometry outperforms most of the enhanced fin patterns such as of Type II and Type Ill at the fully developed region. This is because a close spacing prevents 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 is more beneficial than that of plain fin geometry. In association with the VG-1 criteria (same pumping power and same heat transfer capacity), the results show that effective reduction of surface area can be achieved when the frontal velocities are at 3-5 m s(-1) and the fin patterns are triangular, triangular attack, or two-groups dimple. The result from the present experiment suggests that the asymmetric combination such as using loose vortex generator (Type IV) can be quite effective. The triangular attack vortex generator is regarded as the optimum enhancement design for it could reduce 12-15% surface area at a frontal velocity around 3-5 m s(-1). The asymmetric design is still applicable even when the fin pitch is reduced to 1 mm. (C) 2010 Elsevier Ltd. All rights reserved.
Investigation of the performance of pulsating heat pipe subject to uniform/alternating tube diameters
(2014-04-01)
Tseng, Chih-Yung
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Yang, Kai-Shing
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Chien, Kuo-Hsiang
;
Jeng, Ming-Shan
;
Wang, Chi-Chuan
The present study examines the performance of closed-loop pulsating heat pipes (CLPHPs) with an ID of 2.4 mm. The effect of uniform and alternating tube diameter on the performance is investigated. The working fluids include distilled water, methanol and HFE-7100. Tests are performed with both horizontal and vertical arrangement. For the horizontal arrangement, when compared to uniform design, the alternating channel design can be started at a rather low heat input with a much smaller thermal resistance. Normally the thermal resistance is decreased with the rise of heat input, and reveals a minimum value at a certain heat input followed by shows a marginal rise when the heat input is increased further. Both uniform and alternating design reveals the similar trend. For the vertical arrangement, the thermal resistance is much lower than that in horizontal arrangement. Different from that in horizontal arrangement, the thermal resistance shows a continuous decline against heat input for all the working fluids. For a low input power, CLPHP with HFE-7100 shows the least thermal resistance. By contrast, CLPHP with distilled water shows the smallest thermal resistance when the input power is increased over 60 W. (C) 2014 Elsevier Inc. 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.
Theoretical study of oscillatory phenomena in a horizontal closed-loop pulsating heat pipe with asymmetrical arrayed minichannel
(2012-08-01)
Chiang, Ching-Ming
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Chien, Kuo-Hsiang
;
Chen, Han-Ming
;
Wang, Chi-Chuan
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機械工程學系
"This study develops an analytical model applicable for predicting the oscillatory motion of a pulsating heat pipe (PHP) with asymmetrical arrayed minichannel configuration. The analytic model takes into account the temperature difference between the average evaporating region and the average condensing region as the thermally driven force for the oscillatory motion. It is found that the dominant parameters affecting the PHP include configurations and dimensions of the flow channel, the number of turns, the filled liquid ratio, the frequency ratio, the operating temperature, and the temperature difference between the average evaporating region and the average condensing region are investigated in this study. The calculated results show that the closed-loop pulsating heat pipe with asymmetrical arrayed minichannel under lower number of turns, lower filled liquid ratio, higher operating temperature and higher temperature difference between the average evaporating region and the average condensing region for the frequency ratio of unity could attain a better performance of the oscillatory motions. (C) 2012 Elsevier Ltd. All rights reserved."