陣列式針狀電極應用於EHD熱傳增強技術

EHD Enhanced Heat Transfer with Needle-Arrayed Electrodes

李幸勇(Hsing-Yung Li)

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(2006年)

摘要

本研究的主要目的是為了增強自然對流下的熱傳行為，為了有效降低對流阻抗，實驗方法採用主動式EHD(electrohydrodynamics)技術配合被動式熱沈，產生電暈風並提升熱傳能力。本文分別以消耗電壓與耗能的觀點來探討電極設計性能的好壞，利用外加直流高壓電場，在施加電壓0∼18kV的實驗範圍內，對流係數最高可提升為自然對流時的4.5倍。實驗結果顯示負電暈有著比正電暈更小的門檻電壓，熱傳效果也優於正電暈。以電壓的觀點而言，不同的電極高度將有著不同的最佳電極密度，電極數目太少與散熱器的幾何干擾都會使得實際有效熱交換的面積受到限制；但若以EHD做功效率而言，電極太密或電極距離太近，也分別會因流場的渦流現象以及局部的流場擾動行為，使得熱交換效率不佳，降低熱傳效果。因此在設計電極時，必須在電壓以及消耗功率間尋求平衡點。

關鍵字

電液動力學 ； 電暈氣流 ； 增強對流

並列摘要

Heat transfer enhanced by electrohydrodynamics (EHD) is experimentally investigated in this work. The system of heat sinks with EHD can effectively increase the rate of heat transfer under natural convection due to the corona wind generated by EHD. The design of electrodes in the system of heat sinks with EHD is studied according to the required voltage and power consumption. The maximum heat transfer coefficient with EHD is greater than that without EHD by four and half times within the operating voltage range of 0 ~ 18kV. The results reveal that both the heat transfer rate and threshold voltage for negative corona are better than those for positive one. For a fixed voltage, the optimal density of electrodes depends on the height of electrode position. The area of heat removal for EHD will be limited by a small density of electrodes or the configuration of heat sinks. However, form the viewpoint of power consumption, the great density of electrodes will result in the flow recirculation and the local flow perturbation; thereby reduce the heat transfer rate. Both the voltage and power consumption must be considered in the design of EHD system.

並列關鍵字

electrohydrodynamics ； corona wind ； enhanced convection

參考文獻

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