- 學位論文
靜電致振與電暈風複合式強化散熱之數值模擬
Numerical Simulation of Heat Transfer Enhancement by Combining Corona Wind and Electrostatic Vibration
摘要
本研究應用高階通量限制函數對純電暈風與複合式電暈風之物理場之耦合計算優化，達到提升計算精確性與穩定性，使模擬結果與實驗結果更為匹配。在以有限容積法為基礎的數值計算方法模擬梯度變化極大的情況時(例如階梯函數)，傳統的離散方法常會產生數值擴散或數值震盪等問題，前者會使計算精度降低，後者會使計算不穩定甚至導致發散，本文所使用之高階通量函數具有偵測局部梯度變化，並依據偵測結果調整離散方法，使計算結果不致於產生過大的數值擴散與震盪，此方法能有效克服計算電暈風現象所遇到的難處：在放電電極尖端附近區域的電荷密度分布與速度分布會因電暈現象產生極大的梯度變化。 本研究針對電暈風現象測試數種不同之高階通量限制函數，分析各種限制函數對於計算電暈風現象的穩定性與準確性，並透過與實驗數據比對趨勢，選擇Van-Leer法作為分析所使用之高階通量限制函數。 模擬結果與實驗結果相比，因為二維假設導致模擬結果之衝擊現象可能較實驗強，進而使熱傳係數在所有條件下均高於實驗量測結果；在模擬結果中發現，電暈風熱傳增強之機制是受衝擊冷卻現象所主導，純電暈風能在加熱板中心形成較強的衝擊流現象，而複合式電暈風的振動雖然會使會使主要衝擊區域增加，但最大局部熱傳係數會下降約30%。基於以上結果，純電暈風具有較好的整體散熱效果，而複合式電暈風具有較均勻的散熱效果。
並列摘要
In this study, a higher-order flux limitation function was used to optimize the coupling calculations under the physical field of pure corona wind and composite corona wind, so as to improve the accuracy and stability of the calculation and make the simulation results more closely match the experimental results. When the numerical calculation method based on the finite volume method is used to simulate a situation where the gradient changes greatly (such as a step function), the traditional discrete method often produces problems such as numerical diffusion or numerical oscillation. The former will reduce the calculation accuracy, and the latter will make the calculation unstable or even cause divergence. . The high-order flux function used in this article can detect local gradient changes and adjust the discrete method based on the detection results so that the calculation results do not cause excessive numerical diffusion and oscillation. This method can effectively overcome the difficulties encountered in the calculation of the corona wind phenomenon：There is a great gradient change of the charge density distribution and velocity distribution in the area near the tip of the discharge electrode due to the corona phenomenon. This study tested several different high-order flux limitation functions for the corona wind phenomenon, analyzed and compared the stability and accuracy of various limitation functions when calculating the corona wind phenomenon, and compared them with experimental data to select appropriate limits. Function to analyze the phenomenon of pure corona wind and composite corona wind, and compares the trend with experimental data to select the Van-Leer method used in the analysis. After comparing the simulation results with the experimental results, it was found that the two-dimensional hypothesis would cause the impact phenomenon in the simulation results to be stronger than the experimental results, thereby making the heat transfer coefficient higher than the experimental measurement results under all conditions. It is shown that the mechanism of enhanced heat transfer from corona wind is dominated by the impact cooling phenomenon. Pure corona wind energy forms a strong impinging flow phenomenon in the center of the heating plate. Although the vibration of the composite corona wind will increase the main impact area, the maximum local heat transfer coefficient will decrease by about 30%. Based on the above results, pure corona wind has a better overall heat dissipation effect, while composite corona wind has a more uniform heat dissipation effect.