臺灣博碩士論文加值系統

本研究以壓電風扇之散熱為主軸，使用PIV高速粒子影像測速法分析不同扇葉的流場，探討其散熱之熱阻值與流場之間的關係。前人研究主要著重在各種參數的散熱效益，尤其是壓電風扇的擺放位置與鳍片設計等，較少探討壓電風扇的流場量測與散熱原因，本研究將深入探討不同扇葉的散熱機制，藉由實驗來解釋其散熱機制如何運作。
為了探討不同扇葉的基本特性，本研究將實驗分為常溫與加熱情況，在常溫下先觀察各種扇葉的流場結構與速度分布，再放入加熱流場中對加熱板進行散熱，並利用加熱板內三個不同位置的熱電偶計算表面溫度與熱通量，進而得到其熱阻值，同時觀察流場變化，分析不同扇葉之熱阻值不同的原因。
本研究對於不同扇葉的散熱特性如下：(1) 扇葉前緣寬度越小會產生較大的共振頻率，頻率越高散熱效果越好。(2) 在共振頻率相同的情況下，倒梯形扇葉因為其扇葉漸縮的特性，能夠在上游造成集中的衝流帶入加熱板中，使得熱阻值最低；而梯形扇葉則因衝流範圍太大，在加熱板上方的空氣會造成短時間滯留導致散熱效果較差。 (3) 壓電片受到溫度的影響很大，本研究使用的壓電片在約60 ℃開始振幅大幅降低，並顫動產生大量的振動熱使溫度持續升高至燒壞，若要使用壓電風扇散熱，建議挑選居禮溫度較高的壓電片，以避免類似情況發生。
本研究歸納之壓電風扇扇葉的流場特性，可使用在電子元件的散熱上，從幾何空間中挑選較佳的扇葉形狀來幫助散熱，使得電子元件工作溫度降低讓其長久使用的改善。

Effect of the piezoelectric fan with different shapes on cooling the heated plate has been investigated experimentally. Previous studies focused mainly on the cooling effectiveness under various parameters, especially the piezoelectric fan of its location and the heat sink of its fin design, but less exploring their transient flow structure and mechanism. Herein, we observe the air flow near the heated plate and illustrate the mechanism with velocity and vorticity distribution of hot flow.
Three blade shapes of piezoelectric fans– trapezoid, rectangle, and invert trapezoid were analyzed at the similar frequency. Trapezoidal shapes have wide root and short leading edge of the blade, and invert-trapezoidal shapes are opposite. The piezoelectric fan was vibrating up and down at 15 mm above the ground parallels the heated plate. To explore the relationship between the thermal resistance and the flow structure, we measured velocity, vorticity and thermal resistance via high-speed particle image velocimetry (PIV) and thermocouples embedded in the heated device.
The results reveal that the thermal resistance in invert-trapezoidal shape is 5-9 % less than in other shapes at the similar frequency. Because invert-trapezoidal shape generates more concentrated downward oscillating airflow, the flow is separated into left and right airflows and takes the heat away from the plate after arriving the heated plate. This forced convection enhance the heat dissipation and decreases thermal resistance between the hot plate and the surroundings. However, downward airflow generated by the trapezoidal shape is so wide that it cannot be spilt easily onto the heated plate.
Our research for the flow characteristics of the piezoelectric of different fan shapes can be applied to the cooling electronic devices. By selecting an invert-trapezoid fan shape, more heat can be dissipated from electronic devices. Therefore, the enhancement of heat transfer which sheds light on the concept of optimal design for cooling devices effectively extends the lifespan of electronics and improves their performance.

目錄
口試委員審定書 i
誌謝 ii
摘要 iii
Abstract iv
目錄 vi
圖表目錄 x
符號說明 xiv
第一章 前言 1
1-1 研究背景 1
1-2 研究動機 1
第二章 文獻回顧 3
2-1 文獻回顧架構 3
2-2 壓電風扇結構 4
2-2.1 壓電材料 4
2-2.2 壓電風扇基本結構 4
2-3 壓電風扇基本原理與流場特性 5
2-3.1 壓電效應 5
2-3.2 壓電參數 7
2-3.3 流場特性 9
2-4 壓電風扇參數 10
2-4.1 自然共振頻率與扇葉形狀 10
2-4.2 風扇位置與擺動方向 11
2-4.3 黏著材料 13
2-4.4 攻角 15
2-4.5 風扇離地高度 16
2-4.6 風扇相位 16
2-4.7 扇葉形狀 18
2-4.8 散熱鰭片 19
2-5 自然對流 20
2-6 模擬與應用 21
第三章 研究方法 23
3-1 研究架構 23
3-2 物理模型 23
3-3 無因次分析 24
3-3.1 扇葉形狀設計 28
3-3.2 扇葉材質 30
3-3.3 壓電片材質 32
3-3.4 擺放方式 33
3-4 高速粒子影像測速法 (PIV) 與分析 34
3-4.1 高速攝影機與鏡頭 36
3-4.2 光學鏡組 38
3-4.3 雷射系統 38
3-4.4 觀測箱 40
3-4.5 分析方法 41
3-5 紅外線測溫法 42
3-5.1 紅外線熱像測溫法與分析 44
3-5.2 加熱裝置與溫度監控儀 46
3-5.3 分析方法 48
第四章 實驗結果與討論 50
4-1 不同扇葉形狀之自然頻率與消耗功率探討 50
4-1.1 扇葉前緣寬度與自然頻率 50
4-1.2 扇葉面積與自然頻率 52
4-1.3 扇葉面積與消耗功率 52
4-2 不同扇葉之常溫流場 53
4-2.1 不同面積之平均常溫流場比較 53
4-2.2 不同形狀之平均常溫流場比較 55
4-3 溫度對壓電風扇的影響 58
4-4 相同面積、不同形狀扇葉之散熱分析 60
4-4.1 常溫與加熱流場比較 60
4-4.2 加熱流場之散熱效益分析 62
4-5 相同前緣寬度與頻率、不同形狀扇葉之散熱分析 66
4-5.1 流場與熱場之實驗結果 66
4-5.2 不同扇葉之中心流場切面(觀察截面4)比較 69
4-5.3 不同扇葉之加熱橫切面流場(觀察截面3)比較 75
4-5.4 不同扇葉之扇葉橫切面流場(觀察截面1)比較 79
4-5.5 壓電風扇扇葉形狀對散熱的影響 83
第五章 結論與未來展望 84
5-1 結論 84
5-2 未來展望 85
5-3 碩士論文進度甘梯圖 86
參考文獻 87

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