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🏛️國立陽明交通大學機構典藏

Access type: Metadata onlyAuthor: search.filters.author.Chen, Ing Youn

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    Influence of electrode configuration on the heat transfer performance of a LED heat source
    (2014-10-01)
    Chen, Ing Youn
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    Chen, Chien-Jen
    ;
    Wang, Chi-Chuan
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    機械工程學系
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    Department of Mechanical Engineering
    In this study, the effects of electrode configuration on the cooling of LED are presented. A total of six needle type electrodes, including sharp, 0.08, 0.12, 0.37, 0.49 R and flat tip, are used to generate ionic wind for cooling of the LED. The effects of electrode configuration, vertical separation height, and tilt angle on the cooling performance of a LED are reported in this study. It is found that the thermal resistance is reduced with the supplied voltage and a maximum 50% reduction is achieved before the spark-over voltage. For the same supplied voltage, the thermal resistance with a larger vertical separation is also higher. However, the operational range is also longer. The effect of tilt angle on the cooling performance of LED depends on the supplied voltage. With a supplied voltage being less than 6.5 kV, it is found that the thermal resistance is increased when the tilt angle is reduced with a tip radius of 0.12 R. However, the trend is reversed when the supplied voltage is higher than 6.5 kV where the thermal resistance of a smaller tilt angle is lower than that of a larger tilt angle. For the same mesh ground, the effect of electrode configurations cast little influence on the final thermal resistance. All the electrodes show an approximately 50% reduction of thermal resistance in association with its original thermal resistance. However, the corresponding threshold voltage and operational voltage differs significantly. The threshold voltage is lowest for the sharp needle and is increased with the rise of tip radius. On the other hand, the corresponding operational range becomes narrower when the tip radius is increased. Yet the spark-over voltage is also insensitive to change of electrode configuration. (C) 2014 Elsevier Ltd. All rights reserved.
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    Two-phase pressure drops and flow pattern observations in 90 degrees bends subject to upward, downward and horizontal arrangements
    (2015-11-01)
    Hsu, Li-Chieh
    ;
    Chen, Ing Youn
    ;
    Chyu, Chien-Min
    ;
    Wang, Chi-Chuan
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    機械工程學系
    In this study, single-phase/two-phase frictional characteristics and flow patterns of 900 bends are experimentally investigated. The two bends have inner diameters (D) of 5.5 and 9.5 mm with tube curvature ratio (2R/D) of 5.4 and 4.2, respectively. The bends are installed either an upward, horizontal or downward arrangement. For results concerned with single-phase flow, the bend friction factor (f(B)) is always greater than that of the straight tubes at the same liquid Reynolds number. On the other hand, the f(B) values for D = 9.5 mm with smaller curvature ratio are greater than those of D = 5.5 mm. The resultant two-phase frictional pressure drops of 90 bend are well predicted by the Sanchez Silva et al. [14]\'s correlation. For the two-phase frictional pressure gradient, the upward arrangement is greater than that of the horizontal arrangement due to swirled motion and liquid flow reversal. The flow reversals are observed for upward flow arrangement at specific flow pattern and pressure gradient. However, no swirled motion and liquid flow reversal is seen in the downward arrangement. As mass flux and quality increase, the differences of pressure drop among the three arrangements are getting smaller due to the appreciable offset by the rising flow inertia. Meanwhile, the liquid flow reversal is more evidently observed in the large diameter bend. Flow pattern map showing the region of liquid flow reversal is shown on the diagram of the superficial gas velocity (U-GS) versus superficial liquid velocity (U-LS). The region for liquid flow reversal for D = 9.5 mm is much greater than that of D = 5.5 mm. For D = 5 mm, there is no liquid flow reversal when U-GS is above 2 m/s. On the other hand, the threshold value is raised to 4 m/s for the 9.5 mm internal diameter tube. (C) 2015 Elsevier Inc. All rights reserved.