臺灣博碩士論文加值系統

隨著科技的進步，高功率LED使用的範圍越來越廣，在不同工作環境下所會遇到的散熱問題也更需要去各別討論。汽車LED頭燈使用的LED主要以高功率為主，且因使用環境為封閉空間且位於汽車引擎旁，故對於高功率LED來說散熱模組更是不可或缺。由於LED散熱模組在封閉環境下工作會產生溫度分層之散熱問題，而一般LED散熱模組設計之方向並無法改善封閉空間之散熱問題，故研究利用煙囪來改善此散熱問題。
本研究設計下煙囪與LED散熱模組進行結合，利用下煙囪之幾何來改善封閉空間之散熱問題，並以擋板設計、增加下煙囪出口寬度來提升下煙囪之效果，但由模擬分析的結果知道下煙囪之幾何設計並不能產生明顯之煙囪效應，故再由煙囪效應文獻得知利用延伸下煙囪出口高度可產生煙囪效應，使得引進更多的空氣進入煙囪裡達到提升散熱效果的目的，讓LED散熱模組在與煙囪結合後能夠使LED溫度下降近4.6℃。最後將煙囪散熱模組運用於H牌汽車近光燈上，利用模擬分析來與原近光燈散熱模組做比較，可以發現煙囪散熱模組確實改善了原近光燈的散熱模組不能解決的溫度分層問題，並且LED溫度還比原散熱模組的LED溫度低3.8~4.6℃，且煙囪散熱模組之散熱鰭片的散熱面積比原近光燈的散熱模組還少20％，故本研究所建立的LED煙囪散熱模組設計，於封閉環境下能有更好的散熱效果及實用性。

LED vehicle headlamps consist largely of several high-power LEDs with the thermal module inside an enclosed space, and locate near the car engine which represents a high-temperature environment. Certainly, the enclosed space and engine compartment make the thermal management of LED headlamp becoming an indispensable and challenging task. Obviously, the temperature stratification inside this bounded region is an unfavorable phenomenon for the natural-convection thermal module and becomes the topic of this thesis. This study utilizes the chimney effect to achieve a more uniform temperature distribution and thus enhance the heat dissipation ability. First of all, an enclosed volume with a similar size like vehicle headlamp is selected for executing the parametric study on the chimney geometry. Several important results are obtained and verified via both numerical and experimental means on the chimney design. Among these alternatives, enlarging the chimney exit area, extending the length of chimney, and adding guide plate between sink and chimney are the most effective strategies to eliminate the undesirable temperature stratification and induce more airflow to the fin passages. Also, a significant 4.6℃ decrease on LED junction temperature is found on the best design of chimney-enhanced heat sink.
Thereafter, these approved guidelines are applied to design the chimney-enhanced thermal module for a commercial LED headlamp. Besides, the numerical flow visualization is performed and observed carefully to check its influence on the thermal dissipating ability. As a result, the temperature-stratification phenomenon is largely improved and a range of 3.8~4.6℃ reduction on LED temperatures are identified for this innovative chimney thermal module, which has only 80% cooling area compared with the original thermal design. In conclusions, this work not only successfully demonstrates the cooling enhancement of chimney design, bust also provides a systematic scheme and guidelines to design an appropriate chimney-enhanced thermal module for the enclosed-space applications.

摘要….. I
Abstract.. III
致謝……. V
目錄….. VI
圖索引… XI
表索引.. XVII
符號索引 XIX
第一章 緒論 1
1.1 前言 1
1.2 LED散熱元件介紹與討論 4
1.2.1 主動式散熱元件 7
1.2.2 被動式散熱元件 10
1.3 文獻回顧 14
1.3.1 自然對流熱傳之散熱鰭片應用 15
1.3.2 煙囪效應 17
1.4 研究動機與方法 20
第二章 物理模式與理論分析 27
2.1 熱傳遞原理與熱阻定義 27
2.1.1 熱傳遞原理 27
2.1.2 熱阻定義 30
2.1.3 LED之熱阻結構 31
2.2 自然對流下之散熱鰭片設計 33
2.2.1 流體流動型態的判定 34
2.2.2 鰭片之最佳間距 36
第三章 數值方法與實驗設備 44
3.1 統御方程式 44
3.2 數值計算理論 49
3.2.1 離散化方式 49
3.2.2 壓力與速度耦合的處裡 53
3.2.3 數值求解流程 55
3.3 數值邊界條件設定 56
3.4 實驗設備 59
3.4.1 恆溫環境量測與資料擷取系統 65
3.4.2 溫度感測器與校正 70
第四章 封閉空間內煙囪散熱模組設計 74
4.1 LED發熱瓦數驗證方法 74
4.1.1 實驗方式與數值模擬方法 75
4.1.2 LED發熱瓦數驗證 79
4.2 封閉空間對LED散熱模組性能的影響 85
4.2.1 封閉外殼大小與網格獨立分析 85
4.2.2 有/無封閉空間之散熱模組性能分析 89
4.3 具下煙囪設計之散熱模組 94
4.3.1 封閉空間LED散熱模組支架設計 94
4.3.2 下煙囪設計 95
4.4 下煙囪設計之參數分析 111
4.4.1 於下煙囪裡不同擺放方向之散熱鰭片 111
4.4.2 下煙囪入口位置與外殼底部距離討論 119
4.5 擋板或減少流場阻礙之設計 123
4.5.1 擋板設計 123
4.5.2 減少下煙囪流場阻礙 130
4.6 延伸下煙囪設計 142
第五章 具煙囪設計之散熱模組於LED汽車頭燈之實驗與應用 151
5.1 具煙囪設計之散熱模組參數實驗 151
5.1.1 實驗設備建立 152
5.1.2 實驗結果 162
5.2 原始LED車頭燈之散熱模組分析 166
5.2.1 車頭燈CAD建立 167
5.2.2 近光燈原散熱模組之LED轉熱比驗證 177
5.2.3 近光燈原散熱模組之模擬分析 182
5.3 具煙囪設計之散熱模組於LED汽車頭燈之應用 185
5.3.1 近光燈煙囪散熱模組設計 185
5.3.2 近光燈煙囪散熱模組之模擬分析 187
第六章 結論與建議 199
6.1 結論 199
6.2 建議 205
參考文獻 208

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