| 摘要: | 近年來由於電子產業發展的進步，電子元件體積與重量的減少使得單位面積之熱量增加，因此，發展出有效之散熱裝置是目前最重要的目標。本數值研究利用電液動(electrohydrodynamic, EHD)產生的電暈風增強流道中之熱對流能力，以提升熱傳效果。本文藉由數值模擬及與實驗數據作比對，以驗證本文的數值模式，也釐清EHD技術的物理機制與散熱效果。 首先以針式-平板式與線式-網格式兩種幾何外型之電極，針對電壓與電流、流體流速、熱對流係數作驗證，證明模式建立之正確性。接著以線式-平板式EHD電極，在不同之供應電壓(3~6 kV)、放電電極至收集電極之間距(0.00175、0.00275 m)與入口端為圓柱狀(例1)與一般平板狀(例2)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。數值模擬顯示最佳熱傳增強效率其熱對流通量，約為無EHD效應的一般流場的1.6倍。數值模擬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。例1的電極安置之散熱效能會較例2的電極安置高約14.2 %，但前者的電極消耗功率高於後者約18 mW。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。依據本文研究，EHD技術確實能對管流的熱傳效果有顯著的改善。 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. First, 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 (3~6 kV), different electrode separations (0.00175 and 0.00275 m) and different collecting electrode geometries on heat transfer were discussed, including cylindrical (case 1) and normal plate (case 2) 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 (Nusselt no.) and heat transfer enhancement. The electrode separation is inversely proportional to the flow velocity, convective coefficient, Nu (Nusselt number) and heat transfer enhancement. The heat transfer efficiency in case 1 were 14.2 % better than that of case 2, however, the former consumes 18 mW higher than the latter. The space of electrode is inversely proportional to the flow velocity, heat convection coefficeint, Nu and heat transfer enhancement. Base on present study, EHD technology indeed provide a significant cooling effect on the channel flow. |
