Browsing by Author "Yang, Kai-Shing"

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A Comparative Study of Nozzle/Diffuser Micropumps with Novel Valves
(2012-02-01)
Yang, Kai-Shing
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Chao, Tzu-Feng
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Chen, Ing Youn
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Wang, Chi-Chuan
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Shyu, Jin-Cherng
This study conducts an experimental study concerning the improvement of nozzle/diffuser micropump design using some novel no-moving-part valves. A total of three micropumps, including two enhancement structures having two-fin or obstacle structure and one conventional micro nozzle/diffuser design, are made and tested in this study. It is found that dramatic increase of the pressure drops across the designed micro nozzles/diffusers are seen when the obstacle or fin structure is added. The resultant maximum flow rates are 47.07 mm(3)/s and 53.39 mm(3)/s, respectively, for the conventional micro nozzle/diffuser and the added two-fin structure in micro nozzle/diffuser operated at a frequency of 400 Hz. Yet the mass flow rate for two-fin design surpasses that of conventional one when the frequency is below 425 Hz but the trend is reversed with a further increase of frequency. This is because the maximum efficiency ratio improvement for added two-fin is appreciably higher than the other design at a lower operating frequency. In the meantime, despite the efficiency ratio of the obstacle structure also reveals a similar trend as that of two-fin design, its significant pressure drop (flow resistance) had offset its superiority at low operating frequency, thereby leading to a lesser flow rate throughout the test range.
A Novel Condensate-Free Refrigerated Cold Plate for Electronic Cooling
(2010-01-01)
Wu, Yu-Lieh
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Yang, Kai-Shing
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Chen, Min-Yi
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Wang, Chi-Chuan
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機械工程學系
A novel cooling design featuring a two-stage expansion process is proposed in this study. Without any help from insulation, the design can minimize or even entirely eliminate condensate formation outside the cold-plate surface even for a very low evaporation temperature. The design incorporates a double-pipe inlet/outlet and a two-container cold plate, and its performance is compared to a conventional cold plate. For the conventional cold plate, the outlet pressure/temperature hold quite steadily at a light heat load, and the outlet pressure/temperature shows a substantial rise when the refrigerant is completely evaporated. The outlet pressure/temperature of the condensate-free cold plate shows an opposite trend at a heavy heat loading. The benefit of this characteristic is that the wall surface temperature and the outlet temperature of the cold plate can be maintained comparatively more steady than the conventional cold plate.
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
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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
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Wu, Shih-Kuo
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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.
A novel oxidized composite braided wires wick structure applicable for ultra-thin flattened heat pipes
(2017-11-01)
Yang, Kai-Shing
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Tu, Cheng-Wei
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Zhang, Wen-Hua
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Yeh, Chih-Ting
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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.
A Novel Thermal Module with 3-D Configuration Pulsating Heat Pipe for High-Flux Applications
(2018-12-01)
Tseng, Chih-Yung
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Wu, Ho-Meng
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Wong, Shwin-Chung
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Yang, Kai-Shing
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Wang, Chi-Chuan
A pulsating heat pipe (PHP) contains a wickless design with aligned serpentine tube configuration whose simple structure offers a comparatively easy manufacturing capability. The bends with large curvature are often used for serpentine PHPs. This eventually results in a decline in effective contact surface area between evaporator/condenser and PHP circuitry, thereby impairing the benefit of the wickless design of a PHP. A novel thermal module featuring a 3-D configuration pulsating heat pipe, an evaporator, and a fin-and-tube condenser is proposed to tackle the high-flux application. Methanol is used as the working fluid with a filling ratio of around 60%. Test results indicate the thermal resistance of the proposed module varies from 0.148 K/W to 0.0595 K/W when the supplied power changes from 100 to 1000 W. The proposed thermal module can handle a supplied power up to 1 kW and the corresponding power or heat flux is much higher than any existing literatures.
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
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Lee, Ming-Tsang
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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.
An experimental investigation of air cooling thermal module using various enhancements at low Reynolds number region
(2010-12-01)
Yang, Kai-Shing
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Li, Shu-Lin
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Chen, Ing Youn
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Chien, Kuo-Hsiang
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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.
An experimental study on the heat dissipation of LED lighting module using metal/carbon foam
(2013-11-01)
Yang, Kai-Shing
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Chung, Chi-Hung
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Lee, Ming-Tsang
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Chiang, Song-Bor
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Wong, Cheng-Chou
In this study, thermal performance of the cooling modules applicable for Par 38 light bulb is investigated. A total of six heat sink modules, including the basic reference design, metal foam, and carbon foam are tested and compared. Tests are performed and analyzed using the transient test method based on JESD51-1 standard. It is found that the thermal resistance from junction to die attach is quite small. By contrast, the thermal resistance of the heat sink dominates the total resistance, and it comprises 55% of the total resistance for the standard heat sink module. With some slight opening on the base plate, the thermal resistance can be improved by approximately 12%. The thermal resistance for the carbon foam having an embedded metal plate shows the least thermal resistance of 1.14 K/W, followed by the carbon foam, and then the metal foam. The lower thermal resistance of carbon foam in association with copper metal foam is due to its higher emissivity. In addition to better heat transfer performance as compared to the standard plate heat sink, the utilization of carbon foam and metal foam can also significantly reduce the weight of the heat sink. In this study, the weight of the heat sink can be reduced as much as 33%. (C) 2013 Elsevier Ltd. All rights reserved.
An investigation of a top-mounted domestic refrigerator
(2010-07-01)
Yang, Kai-Shing
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Chang, Wen-Ruey
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Chen, Ing-Young
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Wang, Chi-Chuan
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機械工程學系
A detailed numerical simulation of the performance of household refrigerator having a top-mount configuration is made in this study, and an experiment is carried out with a real refrigerator for verification. The results indicate the temperature distributions from the numerical simulation are qualitatively in line with the experimental measurements. Cyclic temperature variations occur amid freezer, refrigerating, and vegetable compartments due to on/off control strategy. However, it is found that the temperature variation for freezer and refrigerating compartment are in phase with each other while the temperature variation in vegetable compartment is roughly out-of-phase with the other two compartments. The simulations show that the design of air duct and its locations may impose a detrimental role on the temperature uniformity within the refrigerator, yet the airflow is strongly influenced by gravity. It is also found that the refrigerating compartment possesses the worst temperature non-uniformity. For improving the temperature non-uniformity, a modified design incorporating the air duct design with appropriate locations of the inlet openings in the freezer and refrigerating compartment is proposed. Though these modifications the maximum temperature difference and the root mean-square of temperature variation in refrigerating compartment, had been reduced from 7.17 degrees C to 3.57 degrees C and from 3.17 degrees C to 1.55 degrees C respectively. (C) 2010 Elsevier Ltd. All rights reserved.
Characteristics of flow distribution in compact parallel flow heat exchangers, part I: Typical inlet header
(2011-11-01)
Wang, Chi-Chuan
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Yang, Kai-Shing
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Tsai, Jhong-Syuan
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Chen, Ing Youn
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機械工程學系
This study experimentally and numerically investigates the single-phase flow into parallel flow heat exchangers with inlet and outlet rectangular headers having square cross section and 9 circular tubes. The effects of inlet flow condition, tube diameter, header size, area ratio, flow directions (Z and U-type), as well as the gravity are investigated. The experimental results indicate that flow distribution for U-type flow is more uniform than Z-type flow. Depending on the inlet volumetric flow rate, the flow ratio at the first several tubes can be lower than 50% of the last tube for Z-type arrangement, and this phenomenon becomes more and more pronounced with the rising velocity at the intake conduit. The mal-distribution can be eased via reducing the branching tube size or increasing the entrance settling distance at the intake conduit. It is found that the influence of gravity on mal-distribution is negligible and the mal-distribution is associated with the jet flow pattern. (C) 2011 Elsevier Ltd. All rights reserved.
Characteristics of flow distribution in compact parallel flow heat exchangers, part II: Modified inlet header
(2011-11-01)
Wang, Chi-Chuan
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Yang, Kai-Shing
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Tsai, Jhong-Syuan
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Chen, Ing Youn
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機械工程學系
This study presents the experimental results of liquid flow distribution in compact parallel flow heat exchanger through a rectangular and 5 modified inlet headers (i.e., 1 trapezoidal, one multi-step, 2 baffle plates and 1 baffle tubes header). The basic header has a rectangular shape with 9 x 9 mm cross section and 90 mm long header length having a 4 mm inlet tube for flow into the header and distributed to nine 3 mm parallel tubes with 400 mm length. A jet stream induced at the header inlet associated with vortexes affecting the flow distribution to the front tubes. The flow distribution in the header highly depends on the header shape and the total flow rate. Normally the first several tubes have the lowest flow ratios for the conventional headers and the flow distribution is significantly improved by lifting the jet stream using the modified header with baffle tube, followed by the baffle plate and multi-step header. The baffle tube yields the best flow distribution for it removed the vortex flow, and it is applicable for all the flow rates. (C) 2011 Elsevier Ltd. All rights reserved.
Effect of cannelure fin configuration on compact aircooling heat sink
(2011-07-01)
Wang, Chi-Chuan
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Yang, Kai-Shing
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Liu, Yang-Ping
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Chen, Ing Youn
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機械工程學系
The present study proposed a novel cannelure fin structure applicable to compact air-cooled heat sink under cross flow condition. A total of eight heat sinks were made and tested, including plain fin, oblique dimple type (I), oblique dimple type (II), straight cannelure, full oblique cannelure, half oblique cannelure with dimple/cavity type, half oblique cannelure with dimple/cavity type (II), and full oblique cannelure with dimple/cavity. Test results indicate that the proposed full cannelure fin along with the dimple/cavity structure can attain approximately 25% increase of heat transfer performance, and accompanies a friction reduction of about 20%. Moreover, converse to those interrupted fin or triangular vortex generator, it is found that the proposed fin structure still offers significant augmentation in fully developed region. The observed IR image of the temperature measurement of the test fin configurations also confirms the measurements. (C) 2011 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.
Enhanced cooling for LED lighting using ionic wind
(2013-01-15)
Chen, Ing Youn
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Guo, Mei-Zuo
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Yang, Kai-Shing
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Wang, Chi-Chuan
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機械工程學系
This study employs ionic wind to augment heat transfer of a LED mounted on a substrate. The size of the LED chip is 0.9 mm x 0.9 mm with a nominal power of 1 W. A needle type electrode is used to generate ionic wind with the applied voltage ranging from 4 to 11 kV. The effects of aligned angle, electrode polarity, separation distance, and ground configuration on the thermal resistance of the LED substrate are examined in this study. For the same applied voltage, it appears that the thermal resistance for the negative polarity is lower than that for the positive one and the negative electrode also has a wilder operation range. The thermal resistance can be reduced as much as 50% in the test range. The thermal resistance is slightly reduced when the aligned angle is increased from 0 degrees to 20 degrees, but a further increase of aligned angle casts no further reduction on the thermal resistance. It is found that the influence of vertical separation distance between the needle and ground electrode is moderately higher than that of horizontal separation distance. Test results also indicate that the mesh ground electrode shows moderately lower thermal resistance than those of point or line electrode. (C) 2012 Elsevier Ltd. All rights reserved.
Enhanced dehumidification via hybrid hydrophilic/hydrophobic morphology having wedge gradient and drainage channels
(2019-11-01)
Yang, Kai-Shing
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Huang, Yu-Yang
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Liu, Yao-Hsien
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Wu, Shih-Kuo
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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%.
Experimental investigation of moist air condensation on hydrophilic, hydrophobic, superhydrophilic, and hybrid hydrophobic-hydrophilic surfaces
(2017-12-01)
Yang, Kai-Shing
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Lin, Kai-Hsiang
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Tu, Cheng-Wei
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He, Yu-Zhen
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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.
Heat Transfer and Flow Pattern Characteristics for HFE-7100 Within Microchannel Heat Sinks
(2011)
Yang, Kai-Shing
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Jeng, Yeau-Ren
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Huang, Chun-Min
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Wang, Chi-Chuan
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機械工程學系
This study investigates the heat transfer characteristics and flow pattern for the dielectric fluid HFE-7100 within multiport microchannel heat sinks with hydraulic diameters of 480 m and 790 m. The test results indicate that the heat transfer coefficient for the smaller channel is generally higher than that of the larger channel. It is found that the heat transfer coefficients are roughly independent of heat flux and vapor quality for a modest mass flux ranging from 200 to 400 kg m-2 s-1 at a channel size of 480 m and there is a noticeable increase of heat transfer coefficient with heat flux for hydraulic diameters of 790 m. The difference arises from flow pattern. However, for a smaller mass flux of 100 kg m-2 s-1, the presence of flow reversal at an elevated heat flux for hydraulic diameters of 480 m led to an appreciable drop of heat transfer coefficient. For a larger channel size of 790 m, though the flow reversal is not observed at a larger heat flux, some local early partial dryout still occurs to offset the heat flux contribution and results in an unconceivable influence of heat flux. The measured heat transfer coefficients for hydraulic diameters of 790 m are well predicted by the Cooper correlation. However, the Cooper correlation considerably underpredicts the test data by 35-85% for hydraulic diameters of 480 m. The influence of mass flux on the heat transfer coefficient is quite small for both channels.
Influence of Inlet Configurations on the Refrigerant Distribution of a Dual Cold-Plate System
(2010)
Yang, Kai-Shing
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Yu, Kun-Huang
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Chen, Ing-Youn
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Wang, Chi-Chuan
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電子工程學系及電子研究所
This study examines the refrigerant distribution of a dual cold-plate system subject to the influence of heating load and inlet configurations. Three inlet configurations, namely, uniformly divided, side-entrance, and inlet inclination, are examined. For an unequal heating load for both uniformly divided and side-entrance configurations, it is found that the distribution of mass flow rate subject to the influence of heating load is strongly related to the outlet states of the two cold plates. For the condition where one of the cold plates is in a superheated state while the other is in a saturated state, the mass flow rate pertaining to a fixed heating load is lower than that of a smaller heating load, and the difference increases significantly when the heating load gets smaller. For the condition where both outlet states of cold plate are at superheated states, the mass flow rate for the fixed heating load is about the same for the uniformly divided configuration and is marginally higher than that of the smaller heating load at the side-entrance configuration. The inlet inclination has a moderate influence on the flow distribution; the difference in mass flow rate is as large as 15% when the inclination angle is 10 degrees.
Investigation of Separated Two-Phase Thermosiphon Loop for Relieving the Air-Conditioning Loading in Datacenter
(2019-01-01)
Daraghmeh, Hafiz M.
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Sulaiman, Mohammed W.
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Yang, Kai-Shing
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Wang, Chi-Chuan
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機械工程學系
This study investigates the feasibility of using R-134a filled separated two-phase thermosiphon loop (STPTL) as a free cooling technique in datacenters. Two data center racks one of them is attached with fin and tube thermosiphon were cooled by CRAC unit (computer room air conditioning unit) individually. Thermosiphon can help to partially eliminate the compressor loading of the CRAC; thus, energy saving potential of thermosiphon loop was investigated. The condenser is a water-cooled design and perfluoroalkoxy pipes were used as adiabatic riser/downcomer for easier installation and mobile capability. Tests were conducted with filling ratio ranging from 0 to 90%. The test results indicate that the energy saving increases with the rise of filling ratio and an optimum energy savings of 38.7% can be achieved at filling ratios of 70%, a further increase of filling ratio leads to a reduction in energy saving. At a low filling ratio like 10%, the evaporator starves for refrigerant and a very uneven air temperature distribution occurring at the exit of data rack. The uneven temperature distribution is relieved considerably when the evaporator is fully flooded. It is also found that the energy saving is in line with the rise of system pressure. Overfilling of the evaporator may lead to a decline of system pressure. A lower thermal resistance occurs at high filling ratios and higher ambient temperature.