EHD電極形式對散熱效率之增益分析

Enhancement of the form of electrode of EHD to thermal efficiency analysis.

徐麗惠(Li-Hui Hsu)

指導教授 ： 蔡國隆

國立臺北科技大學/機電學院/車輛工程系所/碩士(2014年)

摘要

近年來由於電子產業發展迅速，電子零件越來越講求輕薄短小使得單位面積之熱量增加，因此如何發展出有效率地散熱裝置成為現今熱傳工程的重要目標。本數值模擬研究利用電液動技術產生的電暈風促使流道產生熱對流效應，藉以提升熱傳效果。本文藉由數值模擬與實驗數據作比對，作模擬模型驗證，亦可釐清EHD技術之物理機制與散熱效果。
首先分別針對針式-平板式與線式-網格式兩種幾何外型之電極，對電壓與電流、流體流速及熱對流係數作驗證。接著再以線式-平板式組合之EHD電極，在不同供應電壓、電極間距與圓柱狀與一般平板狀之收集電極幾何外型，作數值模擬分析，探討其對熱傳效果之影響。數值模擬顯示最佳的熱傳效率其熱對流通量，約為無EHD效應的1.6倍。結果顯示供應電壓與流體流速、熱對流係數、紐塞數與熱傳增加量成正比。而圓柱狀的電極安置之散熱效果較一般平板狀的電極佳，但前者之功率消耗亦高於後者。電極間距會與流體流速、熱對流係數、紐塞數與熱傳增加量成反比。研究結果發現EHD技術確實能對管流中的熱傳效果有顯著的改善。

關鍵字

電液動技術 ； 電暈氣流 ； 增強對流 ； 計算流體力學

並列摘要

This numerical study utilized the electrohydrodynamics (EHD) techniques to generate the corona wind to enhance the heat convection inside the channe, so that the heat transfer . Numerical simulations results were used to compared with experiments to validate present numerical model, also, to clarify the physical mechanism and heat dissipation induced by EHD techniques.
Two kind of electrode geometries setup including the needle-to-plate and the wire-to-grid were implemented. By comparing the applied voltage, corona current, flow velocity and heat transfer coefficient with the experimental data to validate the accuracy of the models. Next, the wire-to-plate geometry was simulated and the effects of different applied voltages, different electrode separations and different collecting electrode geometries on heat transfer were discussed, including cylindrical and normal plate inlet geometry. The results showed that the best convective flux efficiency could reached to 1.6 times of that of the traditional chanel flow without EHD effect. Numerical results show that the applied voltage is directly proportional to the flow velocity, convective coefficient, Nu and heat transfer enhancement. The electrode separation is inversely proportional to the flow velocity, convective coefficient, Nu and heat transfer enhancement. The heat transfer efficiency in cylindrical were better than that of normal plate, however, the former consumes higher than the latter. The space of electrode is inversely proportional to the flow velocity, heat convection coefficient, Nu and heat transfer enhancement. Base on present study, EHD technology indeed provide a significant cooling effect on the channel flow.

並列關鍵字

electrohydrodynamics ； corona wind ； enhancedconvection

參考文獻

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