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A Novel Thermal Module with 3-D Configuration Pulsating Heat Pipe for High-Flux Applications
(2018-12-01)
Tseng, Chih-Yung
;
Wu, Ho-Meng
;
Wong, Shwin-Chung
;
Yang, Kai-Shing
;
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.
Investigation of Separated Two-Phase Thermosiphon Loop for Relieving the Air-Conditioning Loading in Datacenter
(2019-01-01)
Daraghmeh, Hafiz M.
;
Sulaiman, Mohammed W.
;
Yang, Kai-Shing
;
Wang, Chi-Chuan
;
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.
Novel no-moving-part valves for microfluidic devices
(2010-10-01)
Yang, Kai-Shing
;
Chen, Ing-Youn
;
Wang, Chi-Chuan
;
Shyu, Jin-Cherng
;
機械工程學系
This study characterizes and analyzes the performances of micro diffusers/nozzles with five types of enhancement structures and one of conventional micro nozzle/diffuser valve. The pressure drops across the designed micro nozzles/diffusers are found to be increased considerably when the obstacle and fin structure are added. Further, the micro nozzle/diffuser having added circular area reveals the lowest pressure drop, owing to the hydraulic diameter is increased by circular area and lower interface friction. The maximum improvement of the loss coefficient ratio is about 16% for an added 3-fin structure operated at a Reynolds number around 70. Upon this situation, the static rectification efficiency improves 4.43 times than the conventional nozzle/diffuser. Experimental results indicate the performance peaks at a Reynolds number around 70, and an appreciable decline is encountered when the Reynolds number is reduced. It is due to the efficiency ratio of conventional micro nozzle/diffuser significant increases with the Reynolds number.
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
;
Chen, Ing Youn
;
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.
Performance and two-phase flow pattern for micro flat heat pipes
(2014-10-01)
Yang, Kai-Shing
;
Lin, Chen-Chuan
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Shyu, Jin-Cherng
;
Tseng, Chih-Yung
;
Wang, Chi-Chuan
In this study, thermal performance and flow visualization of a double layer flat micro vapor chamber are reported. Two micro vapor chambers having pin fin and pin fin array support structure are fabricated and tested. The micro vapor chambers are composed of silicon and glass wafers having an overall size of 35 x 40 x 1.525 mm. Test results show that both the pin fin and pin fin array vapor chambers show an appreciably lower thermal resistance as compared to the solid silicon counterpart, the thermal resistance of the pin fin vapor chamber is about 52-60% of the solid silicon whereas the corresponding thermal resistance of pin fin array is only 17-20% of the solid silicon. The thermal resistance of the pin fin vapor chamber is moderately increased subject to the increase of supplied power whereas opposite trend is encountered for the pin fin array. The phenomenon is associated with the influence of dry-out phenomenon. It is found that the pin fin array vapor chamber is still in function even for an upside-down arrangement. The thermal resistance, however, is reduced with the rise of tilt angle, and the vertical arrangement gives the lowest thermal resistance. However, the thermal resistance is considerably increased if the heat source is placed upwards, and the corresponding thermal resistance for an upside-down heat source can be threefold higher than that of the vertical arrangement. (C) 2014 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
;
Yang, Kai-Shing
;
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.
An experimental study on the heat dissipation of LED lighting module using metal/carbon foam
(2013-11-01)
Yang, Kai-Shing
;
Chung, Chi-Hung
;
Lee, Ming-Tsang
;
Chiang, Song-Bor
;
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.
Effect of cannelure fin configuration on compact aircooling heat sink
(2011-07-01)
Wang, Chi-Chuan
;
Yang, Kai-Shing
;
Liu, Yang-Ping
;
Chen, Ing Youn
;
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.
Orientation effect on heat transfer of a shrouded LED backlight panel with a plate-fin array
(2013-03-01)
Shyu, Jin-Cherng
;
Hsu, Keng-Wei
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Yang, Kai-Shing
;
Wang, Chi-Chuan
;
機械工程學系
This study reports thermal performance of a shrouded 348 mmx 558 mm aluminum plate-fin heat sink subject to various input powers and orientations. Effects of clearance (C) and the orientation on the heat transfer of the heat sink were investigated. Results show that the clearance effect is detectable only in a "window region" between 5 mm and 10 mm where an appreciable rise of heat transfer coefficient is encountered. As the tilted angle (theta) of the LED panel is increased, the heat transfer coefficient is reduced and the clearance effect on heat transfer becomes more pronounced. The heat transfer coefficients are similar between two cases in which the tilted angles of the LED panel are supplementary irrespective of clearance and input power. Except the cases of a horizontal heat sink, heat transfer coefficient of the shrouded heat sink having a fin array facing downward is usually slightly higher than that having supplementary tilted angle. (C) 2012 Elsevier Ltd. All rights reserved.
Enhanced cooling for LED lighting using ionic wind
(2013-01-15)
Chen, Ing Youn
;
Guo, Mei-Zuo
;
Yang, Kai-Shing
;
Wang, Chi-Chuan
;
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.

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