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Now showing 1 - 8 of 8

Non-Uniform Three-Dimensional Pulsating Heat Pipe for Anti-Gravity High-Flux Applications
(2020-06-01)
Tseng, Chih-Yung
;
Yang, Kai-Shing
;
Wang, Chi-Chuan
;
交大名義發表
;
National Chiao Tung University
This study proposes a novel high-flux pulsating heat pipe that can lift the major constraint of the conventional pulsating heat pipe (PHP) which is unable to function properly upon anti-gravity operations. The proposed PHP introduces additional unbalance force via uneven tube diameter/geometry in the adiabatic sections to tailor the problem in anti-gravity operation. The design contains a three-dimensional configuration circuitry with compact arrangement tubes on the evaporator and condenser. Through this design, the non-uniform three-dimensional pulsating heat pipe (3D-PHP) manipulates the uneven inner diameters of the adiabatic sections to form uneven vapor/liquid distributions in the adiabatic sections to yield a unitary flow pattern that is able to withstand a much higher input power. The present PHP uses methanol as working fluid, with 38% volumetric filling ratio, and has a high-flux of 22.9 W/cm(2)and a low the thermal resistance ratio (Ranti-gravity/Rgravity-assisted) of 1.05 when the input power is 800 W. Both the heat flux and thermal resistance ratio for the proposed design are far better than the existing literature.
Enhanced dehumidification via hybrid hydrophilic/hydrophobic morphology having wedge gradient and drainage channels
(2019-11-01)
Yang, Kai-Shing
;
Huang, Yu-Yang
;
Liu, Yao-Hsien
;
Wu, Shih-Kuo
;
Wang, Chi-Chuan
Heat transfer performance under dehumidifying conditions for hydrophilic, and hybrid surfaces (hydrophilic/hydrophobic) within ambient are reported. The hybrid surface features star-shape morphology that contains hydrophilic interior inside star-shape while maintains a hydrophobic nature in the exterior of the star-shape. The star-shape offers comparatively good collecting capability of water condensate for its wedge gradient can effectively manipulate the surface energy. The mobility of the condensate within the star-shape interior is improved, leading to enhanced condensation heat transfer performance of 3.7 similar to 11.4% when compared to the hydrophilic surface. However, the contact angle hysteresis of the star-shape surface also retains the condensate inside the star-shape interior to some extent. To tackle this problem, a drainage channel alongside the gravity direction is added to the star-shape surface (star_I), and it offers a much better condensate removal, thereby improving the dehumidifying heat transfer performance up to 15.3 similar to 30.4%.
Luminescence material characterizations on laser-phosphor lighting techniques
(2019-03-04)
Yeh, Chih-Ting
;
Chou, Yen-, I
;
Yang, Kai-Shing
;
Wu, Shih-Kuo
;
Wang, Chi-Chuang
This study examines three different types of laser carriers, including the phosphors in silicone (PiS), the phosphor in glass (PiG), and alumina-based ceramic binders (CP), for laser-phosphor lighting characterizations via a laser projector light source module. The thermal influence of heat spreading on these phosphor materials and their luminescence performance is also investigated. The conversion efficiency of PiS, PiG and CP was found to be 29.7%, 34.6% and 31.8%, with their corresponding maximum laser power operations of 3.9 W, 7.9 W, and 17.2 W, respectively. This work further correlates the maximum laser operation power with the thermal conductivity of luminescence material. From the optical engine perspective, it was found that CP exhibits the superior thermal conductivity of 17.0 W/m.K for slight hot-spot IR observation and higher laser power operation. This work finally delivers a CP device for 50.2W maximum laser operation with the operating temperature below 100 degrees C. The simulation is also carried out in order to examine spreading resistance's influence, when subject to convective boundary condition. CP's response sensitivity to heat transfer coefficient was found to be rather small. (C) 2019 Optical Society of America under the terms of the OSA Open Access Publishing Agreement
Investigation of the evacuation pressure on the performance of pulsating heat pipe
(2017-07-01)
Sun, Chien-Hung
;
Tseng, Chih-Yung
;
Yang, Kai-Shing
;
Wu, Shih-Kuo
;
Wang, Chi-Chuan
This study examines the influence of evacuation pressure on the startup and overall performance of pulsating heat pipes (PHP). The outer diameter of the copper tube is 3 mm and 2 mm (double tube design) having a wall thickness of 0.3 mm and 0.2 mm, respectively. The working fluids in this study include water and HFE-7000 with filling ratios around 50%, and the evacuation pressure ranging from 0.01 Torr to atmosphere pressure. For an evacuation pressure of 0.01 Torr at a supplied power of 80 W, the thermal resistance of the PHP filling with water is 0.928 K/W while it is 1.161 K/W for HFE-7000. However, the trend is reversed and the thermal resistance for HFE-7000 is lower than water when the evacuation pressure is increased over 100 Torr. The corresponding effective thermal conductivity of waterfilling PHP reaches 51,448 W/m K in comparison with 12,692 W/m K for HFE-7000. However, the effective thermal conductivity for waterfilling PHP drops appreciably with rising evacuation pressure, and the PHP is not functional at the atmosphere pressure. Conversely, although the effective thermal conductivity for HFE-7000 PHP still drops with the rise of evacuation pressure, the HFE-7000 PHP is still in operation even without any evacuation. The gigantic difference in the startup and performance of PHP is related to the solubility of noncondensable gas amid water and HFE-7000.
A novel oxidized composite braided wires wick structure applicable for ultra-thin flattened heat pipes
(2017-11-01)
Yang, Kai-Shing
;
Tu, Cheng-Wei
;
Zhang, Wen-Hua
;
Yeh, Chih-Ting
;
Wang, Chi-Chuan
This present study proposed a novel low-cost and high performance braided wire wick structure having superhydrophilic treatment applicable for ultra-thin heat pipe. The test wick structures include mono and composite wick structure. The composite braided wire adopts two different diameter wire design, using a large diameter (0.1 mm) in the core while the exterior of the core is covered by smaller diameter copper wire (0.05 mm). The mono design contains only one uniform wire diameter (0.1 mm) in core region. Test results indicate that via oxidizing the surface of the braided wires can largely enhance the surface roughness and result in a much higher capillary force as comparing to the un-oxidized one. In addition, both mono (m-FHP) and composite braided wire (c-FHP) with oxidization could possess a maximum heat transfer capability over 15 W under horizontal operation, and test results showed that the heat transfer capability of composite design outperforms mono one by more than 32.5% in all orientations. It is also found that the filling loading ratio plays essential role on the overall performance of FHP. Either a low filling loading ratio or a high filling loading ratio may yield a lower maximum heat transfer capability and a higher thermal resistance. An optimum filling loading ratio of 125% yields the lowest thermal resistance around 0.12 K/W with the best heat transfer capability of 20W.
Experimental investigation of moist air condensation on hydrophilic, hydrophobic, superhydrophilic, and hybrid hydrophobic-hydrophilic surfaces
(2017-12-01)
Yang, Kai-Shing
;
Lin, Kai-Hsiang
;
Tu, Cheng-Wei
;
He, Yu-Zhen
;
Wang, Chi-Chuan
This study experimentally investigates the condensation performance amid hydrophobic, hydrophilic, superhydrophilic and hydrophobic-hydrophilic hybrid patterned surfaces with air velocity ranging from 0.5 m/s to 4.0 m/s and relative humidity of 85%, 60% and 40%. The hybrid novel surface employs inverted V shape channels design with alternate hydrophilic and hydrophobic channel to direct condensate, and the accumulated condensate is gathered at vertical hydrophilic channel for further effective condensate removal. It is found that the heat transfer coefficient for hydrophobic surface is higher than that of hydrophilic surface irrespective of the operational velocity and relative humidity. Dropwise condensation prevails for the hydrophobic surface and a twig-like structure of condensate is seen for the hydrophilic surface, and this phenomenon becomes more pronounced when the relative humidity is increased. The superhydrophilic surface shows the worst heat transfer performance due to filmwise condensation. The hybrid surface shows superior heat transfer performance over other surfaces. The heat transfer coefficient obtained is around 3-9% higher than that of hydrophobic surface and is about 6-16% higher than hydrophilic one. The proposed novel design offers a shorter cyclic condensate removal time and better condensate drainage. It is found that the maximum diameter.for the hybrid surface is about 80-90% smaller than the hydrophobic surface and the droplet size before falling off is relatively independent of operational velocity. (C) 2017 Elsevier Ltd. All rights reserved.
An experimental and analytical investigation of the photo-thermal-electro characteristics of a high power InGaN LED module
(2016-04-05)
Yang, Kai-Shing
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Ding, Wei-Ting
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Yeh, Chih-Ting
;
Lee, Ming-Tsang
;
Wang, Chi-Chuan
The photo-thermal-electro characteristics of a high power InGaN LED module were studied both experimentally and theoretically. Three types of heat sink substrate composed of two layers of materials were used to investigate the coupled relationships between chip temperature, thermal resistance, input electric power and light emission efficiency. The results showed that the thermal spreading resistance accounts for a significant fraction of the total substrate thermal resistance. The measured thermal resistance of the LED module increased with rising electric power input. Luminescent efficacy measurements revealed that this increase of thermal resistance was the result of increased heat dissipation from the chip due to less efficient conversion of electric power to light output. Furthermore, experimental results showed that the radiant efficiency of the LED decreases with increasing input electric power. The coupled effects of chip temperature, input power and thermal resistance of the substrate are responsible for this efficiency droop. A revised model for estimating the luminous efficacy that takes both thermal and electrical effects into consideration is proposed. It is shown that the efficiency droop of the LED module for all three types of substrates can be clearly demonstrated by using the proposed analysis. (C) 2015 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
;
Yang, Kai-Shing
;
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.

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