Browsing by Author "Shyu, Jin-Cherng"

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A Comparative Study of Nozzle/Diffuser Micropumps with Novel Valves
(2012-02-01)
Yang, Kai-Shing
;
Chao, Tzu-Feng
;
Chen, Ing Youn
;
Wang, Chi-Chuan
;
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.
Investigation of bubble effect in microfluidic fuel cells by a simplified microfluidic reactor
(2010-09-01)
Shyu, Jin-Cherng
;
Wei, Chung-Sheng
;
Lee, Ching-Jiun
;
Wang, Chi-Chuan
;
機械工程學系
This study experimentally examines the influence of two-phase flow on the fluid flow in membraneless microfluidic fuel cells. The gas production rate from such fuel cell is firstly estimated via corresponding electrochemical equations and stoichiometry from the published measured current-voltage curves in the literature to identify the existence of gas bubble. It is observed that O(2) bubble is likely to be generated in Hasegawa's experiment when the current density exceeds 30 mA cm(-2) and 3 mA cm(-2) for volumetric flow rates of 100 mu L min(-1) and 10 mu L min(-1), respectively. Besides, CO(2) bubble is also likely to be presented in the Jayashree's experiment at a current density above 110 mA cm(-2) at their operating volumetric liquid flow rate, 0.3 mL min(-1). Secondly, a 1000-mu m-width and 50-mu m-depth platinum-deposited microfluidic reactor is fabricated and tested to estimate the gas bubble effect on the mixing in the similar microchannel at different volumetric flow rates. Analysis of the mixing along with the flow visualization confirm that the membraneless fuel cell should be free from any bubble, since the mixing index of the two inlet streams with bubble generation is almost five times higher than that without any bubble at the downstream. (C) 2010 Elsevier Ltd. All rights reserved.
Novel no-moving-part valves for microfluidic devices
(2010-10-01)
Yang, Kai-Shing
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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.
Orientation effect on heat transfer of a shrouded LED backlight panel with a plate-fin array
(2013-03-01)
Shyu, Jin-Cherng
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Hsu, Keng-Wei
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Yang, Kai-Shing
;
Wang, Chi-Chuan
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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.
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
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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.
Thermal characterization of shrouded plate fin array on an LED backlight panel
(2011-10-01)
Shyu, Jin-Cherng
;
Hsu, Keng-Wei
;
Yang, Kai-Shing
;
Wang, Chi-Chuan
;
機械工程學系
This study experimentally investigates a 348 mm x 558 mm LED backlight panel consisting of 270 1-W LEDs and a plate-fin heat sink in an acrylic housing. Effects of shroud clearance, obstructions at entrance or exit on the overall performance are also examined. The results show that the heat transfer coefficient is very slightly reduced with the rise of shroud clearance from 0 mm to 5 mm, followed by a notable rise but it peaks at a shroud clearance between 10 and 20 mm. A further increase of shroud clearance leads a marginal decrease of heat transfer coefficient. It is found that the maximum temperatures within the LED panel are not necessarily located at the center region due to the edge effect. On the other hand, the temperature variation along the longitudinal direction indicates a local minimum Nusselt number occurring near the exit of LED panel. This unique phenomenon is associated with the development of velocity and temperature field, and is consistent with previous numerical examinations. On the other hand, the obstruction placed at the exit are often severe than at the entrance. (C) 2011 Elsevier Ltd. All rights reserved.