多重針狀電極在EHD熱傳提升技術之研究

Heat Transfer Enhanced Technology by EHD with Multiple Needle Electrodes

陳柏華

指導教授 ： 許文震

國立清華大學/工學院/動力機械工程學系/碩士(2010年)

摘要

本論文主要探討側向電液動力(EHD)技術增強鰭片的散熱效率，目的在於鰭片的自然對流之外，提升鰭片的散熱性能。此技術為加裝多重針狀電極至鰭片的側面，外加一高壓電場，使電極跟鰭片中間的空氣解離，利用解離產生的離子風，增強鰭片的熱傳效率。在本論文實驗0 ~ 18kV的電壓範圍內，電極數目的多寡會影響其熱傳性能，負電壓下電極與鰭片距離為10mm的時候，最佳為6根電極，能提升原有自然對流的1.78倍熱傳性能。此外施加電壓的極性不同，會讓其電暈放電的機制跟著改變，結果證明負高壓效果優於正高壓。本論文也探討電極擺放高度對熱傳性能的影響，在針狀電極擺在鰭片本身高度一半的位置，在正電壓下熱傳性能提升至自然對流的1.74倍。當環境的濕度改變，空氣中水分子的密度產生變化，此變化會對放電過程造成影響，結果在濕度低的時候，其熱傳性能較好。隨著溼度增加，水分子的增加阻礙離子風產生，進而降低鰭片的熱傳性能。最後本論文以EHD裝置流經的電暈電流、所需消耗的功率及實際鰭片上的接點溫度等參數，來探討EHD技術。

關鍵字

電液動力 ； 熱傳 ； 離子風 ； 針狀電極

並列摘要

In this study, the heat transfer performance of heat sink is enhanced by electrohydrodynamic (EHD) technique imposed on the side edge. The aim of EHD is to increase the heat transfer rate of heat sink under the natural convection. The multiple needle electrodes are installed at the side of heat sink with a high voltage electric field applied between the heat sink and electrodes. During the voltage discharge process, the air in the electric field is ionized and then the heat dissipation will be enhanced by these moving ionized molecules which is called ionic winds. The heat transfer performance can be affected by the numbers of electrodes within the operating voltage range of 0-18 kV. For 10mm of the distance between the electrodes and the sink and negative voltage, 6 needle electrodes achieve the best heat transfer performance. The performance is 1.78 times than that for the sink only under the natural convection. Moreover, the mechanism of corona discharge can be changed due to the difference of voltage polarity. The cases for a negative voltage are better than those for a positive one. The effect of height of electrodes on heat dissipation is also taken into account in this study. When the needle electrodes are placed at the middle of height of heat sinks, the performance is enhanced 1.74 times. With an increase in humidity, the occurrence of ionic wind is retarded by these additional water molecules and thereby the heat dissipation of heat sink is decreased. Finally, the various systematic parameters such as the corona current across the EHD device, the power consumption of EHD and the junction temperature are discussed for the problem of interest.

並列關鍵字

electrohydrodynamics ； heat transfer, ； ionic wind ； needle electrode

參考文獻

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