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    Influence of electrode configuration on the heat transfer performance of a LED heat source
    (2014-10-01)
    Chen, Ing Youn
    ;
    Chen, Chien-Jen
    ;
    Wang, Chi-Chuan
    ;
    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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    Effect of oscillatory EHD on the heat transfer performance of a flat plate
    (2013-06-01)
    Sheu, Wen-Junn
    ;
    Hsiao, Jen-Jei
    ;
    Wang, Chi-Chuan
    ;
    機械工程學系
    ;
    Department of Mechanical Engineering
    The present study investigates the effect of oscillatory EHD on the heat transfer performance of a flat plate. A needle type electrode with positive polarity is used to generate ionic wind with applied voltage ranging from 4 to 9.5 kV. The wave forms of the input voltage are either steady or stepped and the frequency ranges from 0.5 to 2 Hz with the separation distance between the electrode and the test plate being 5 and 15 mm, respectively. It is found that at the same applied voltage, the heat transfer performance subject to the oscillatory EHD is always inferior to that of the steady EHD for all frequencies. A parabolic dependence of the ionic current with the supplied voltage is seen under steady EHD operation. However, the ionic current vs. supplied voltage shows a rather linear dependence pertaining to the oscillatory EHD. For a smaller separation distance of 5 mm, the heat transfer performance for f = 0.5 Hz is slightly higher than that of f = 2 Hz. However, the trend is reversed when the separation distance is increased to 15 mm. (C) 2013 Elsevier Ltd. All rights reserved.
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    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.