臺灣博碩士論文加值系統

目前電子元件朝向微小化的發展，大部分電子產品都是應用外加軸流式風扇作動並以空氣強制性能對流方式來散熱，但對可攜式電子產品因其內部空間受限，因此散熱效能急待解決。壓電風扇本身是體積小、重量輕化、低噪音、結構簡單及消耗功率低等特點，適合於可攜式電子組件並解決其有限空間裡的散熱問題。
開放空間條件下，藉由壓電風扇輸入不同的頻率及電壓參數時，壓電風扇葉片產生的振幅大小之關係以及功率消耗等特性，並輔以雷射質點影像測速量測技術，分析壓電風扇於各不同驅動參數下運作的真實三維動態流場。透過數值計算模擬壓電風扇於不同電壓下運作之特性，探討其流線流速分佈情形近似實驗。
實驗結果顯示，壓電風扇的最佳驅動頻率為60Hz具有最大振幅，壓電風扇在快速的週期性振動時，葉尖前端有漸變分離式渦流的現象及往前推進，葉片產生大量的擾動氣流，以強制對流的方式達到散熱之目的。
有限空間條件下，利用漸變分離式渦流的現象以實驗設計法，探討壓電風扇設計置於矩形管，利用壓電效應驅使葉片擺動造成矩形管內產生強制對流。實驗設計法規劃為兩個階段，第一階段以全因子實驗，採用操作矩形管寬度、壓電風扇侵入深度等2個輸入因子進行評估；針對壓電風扇侵入深度為(1/3)L0、(2/3)L0、L0、(4/3)L0及(5/3)L0及五種不同矩形管寬度(4/3)D、(5/3)D、(6/3)D、(7/3)D及(10/3)D，探討壓電風扇於不同的侵入深度及不同的矩形管寬度下，其速度向量、流線及速度分佈等流場現象。
田口分析結果顯示，壓電風扇於矩形管寬度為(4/3)D、(5/3)D及(6/3)D時，當壓電風扇侵入深度越大，壓電風扇的振幅及風速有逐漸減少的現象。當壓電風扇於矩形管寬度為(7/3)D及(10/3)D時，振幅不受矩形管寬度的影響，且壓電風扇於矩形管寬度為(7/3)D，得到全場流域中最大風速平均值為1.7m/s。最後利用田口法實驗陣列去分析各變動量產生反應速度最佳化，當控制因子效應A4B2，其反應速率最大化為1.75 m/s. 壓電風扇於矩形管寬度為(7/3)D且侵入深度(2/3)L_0為最佳實驗設計。
利用在散熱鰭片上壓電風扇的擺放位置，尤以正前方與正上方產生漸變分離式渦流降低散熱鰭片之熱邊界層厚度，當壓電風扇以擠壓與拉伸產生強制對流，若以紊流式渦漩結構破壞熱邊界層有效達到散熱效果。實驗結果顯示，雙壓電風扇涵蓋鰭片面積比單壓電風扇大，可有效的將空氣導入鰭片內部散熱；當雙壓電風扇同向水平擺動，散熱效益隨壓電風扇置於板鰭式散熱器中央位置而提升。不同擺動方式時，以雙壓電風扇垂直擺動之散熱增益優於水平擺動。本研究改變不同參數的實驗中，以雙壓電風扇同向垂直擺動，置於板鰭式散熱器中間位置之熱阻值為3.5℃/W最低，相對具有較高的散熱效益。

Nowadays micro-electromechanical systems (MEMS) have made possible in manufacturing small, slim and lightweight electronic devices. One of the major challenges in these miniaturized devices is their cooling convective system. Technically, the conventional cooling components, such as a rotary fan module are not able to be installed owing to the limited available space. To counter such an issue, a piezoelectric fan (hereafter named as piezofan) is introduced. Piezofan is broadly implemented owing to its unique features, i.e., small-sized, light-weight, low noise and low power consumption. Many types of research pertaining to piezofan have been investigated, but the effect of piezofan in confined space is relatively new. As such, this study aims to investigate the effect of piezofan pertaining to different confined space. First, it investigates the fluid mechanics of a piezoelectric fan operating in its vibration frequency mode. The experimental results show that the optimal driving frequency for the piezoelectric fan is 60 Hz. At this frequency, the thin blade of the piezoelectric fan reaches its maximum vibration amplitude. The flow field visualization in the experiments obtained a comparative investigation of numerical flow simulations. The result shows that the amplitude of the fan blade directly affects flow velocity. The vortex structures exhibit irregular motion once they separate from the blade tip.
The confined spaces are modeled based on different dimensions of rectangular tube (i.e., (4/3)D, (5/3D), (6/3)D, (7/3)D and (10/3)D) which are made from transparent acrylic material. Subsequently, the effects of piezofan pertaining to the depth of confined space (i.e., (1/3) L_0, (2/3) L_0, L_0, (4/3) L_0 and (5/3) L_0) are also investigated. Through this study, velocity vectors, streamlines and performance pertaining to piezofan are observed. The experiment results show that the performance of piezofan is significantly affected by different confined spaces. It is observed that when piezofan is placed in (4/3) D, (5/3) D and (6/3) D, the amplitude of the piezofan and the velocity vector are significantly reduced. However, the amplitude of piezofan is not affected,
when it is placed in (7/3) D and (10/3) D. Also it is observed that at the spaces, the velocity vector is relative high, i.e., 1.7m/s. The three regions explained the operating condition of piezofan in different confined spaces and it contributed to an important technical guide on the implementation of piezofan in confined space and also the design of the cooling system. The Taguchi method is based upon the technique of matrix experiments. The Factor Response Analysis of average velocity is maximized to 1.75 m/s when the Orthogonal Array of experiment data is A4B2. The optimum level and factor were designed when Case A4B2 indicates the inspected confined space is W=(7/3)D with the piezofan is placed inside the confined space with total length H=(2/3)L_0.
Therefore, the thermal resistance is directly proportional to the distance between the blade tip and heat sinks. As previously stated, the piezoelectric fan is driven and decreases the thermal resistance with decreasing distance between the blade tip and plate-fin heat sinks. Besides, thermal performance is the best with the tip of the fan blade at the center of the heat sink. The piezoelectric fan may lead to pushing the air into the heat sinks effectively for cooling. The result of the investigation will focus on decreasing thermal resistance of the heat sinks by operating twin piezoelectric fans. The piezoelectric fans are driven in vertical and horizontal configurations at the side of the heat sinks to investigate thermal performance by infrared thermography. When the piezoelectric fans are at the center of plate-heat sinks, their vibration amplitude covers most of the heat sinks by the period oscillating fan.When the piezoelectric fans are vertical and located at the center of the heat sink. The thermal performance of the heat sink is best respectively 3.5℃/W.

摘要 i
ABSTRACT iii
致謝 v
符號說明 xiv
第一章 緒論 1
1.1研究背景 1
1.2文獻回顧 2
1.2.1質點影像測速系統量測 3
1.2.2壓電風扇流場量測與應用 4
1.2.3壓電風扇漸變分離式渦流探討 5
1.3 研究動機與目的 6
第二章 理論模式建立與分析 13
2.1壓電材料特性 13
2.1.1壓電效應 13
2.1.2壓電材料種類 14
2.1.3機電偶合因子 15
2.1.4機械品質因子 15
2.1.5頻率常數 16
2.1.6功率消耗 16
2.1.7居禮溫度 17
2.2質點影像測速系統之原理 18
2.2.1影像分析之計算 19
2.2.2四分之一法則 21
2.2.3動力速度範圍 21
2.2.4動力空間範圍 22
2.3紅外線量測理論模式建立與分析 22
2.3.1紅外線輻射原理 22
2.3.2電磁波光譜 23
2.3.3黑體放射 23
2.3.4紅外線量測相關參數 25
2.4散熱器之熱傳相關理論 26
2.4.1熱傳導 26
2.4.2熱對流 27
2.4.3熱阻 27
2.4.4薄膜溫度 28
2.4.5葛拉秀夫數 28
2.4.6壓電風扇雷諾數 29
2.4.7強制對流 29
第三章 數值分析 34
3.1計算流體力學的理論模式 34
3.1.1 計算流體力學的介紹 34
3.1.2離散化的目的 34
3.1.3計算流體力學的離散化方法 35
3.2 計算流體力學的基本數值模型 36
3.2.1動態網格 36
3.2.3 幾何模型及邊界條件 39
3.2.4 三維壓電風扇模擬驗證 41
3.3 壓電風扇對後方流場型態的影響 42
第四章 實驗設備與量測 51
4.1實驗設備 51
4.1.1質點影像測速系統 51
4.1.2高速攝影機 52
4.1.3雷射光源 52
4.1.4同步器 53
4.1.5質點影像測速分析軟體 53
4.1.6數據資料分析與圖形化 54
4.1.7煙霧產生器 54
4.1.8壓電風扇 54
4.1.9交流電源供應器 54
4.2實驗方法 56
4.2.1測試件模型 56
4.2.2實驗儀器校正 56
4.2.3實驗步驟 57
4.3 熱傳實驗設備及方法 58
4.3.1紅外線熱像儀設定方式 59
4.3.2測試件模型 60
4.3.3實驗步驟 60
4.3.4量測誤差之不準度 61
4.4 實驗設計法 62
4.4.1實驗設計法原理 62
4.4.2田口設計理論模式 62
4.4.3風扇至於矩形管之實驗因子 64
第五章 結果與討論 79
5.1 輸入電壓及共振頻率與壓電風扇振幅位移關係 79
5.2 壓電風扇後方流場的可視化分析 79
5.3壓電風扇振動後之流場軸向合成力 82
5.4壓電風扇於矩形管內作動之流場分析 82
5.4.1不同壓電風扇侵入深度對流場之影響 83
5.4.2不同矩形管寬度對流場之影響 84
5.5雙壓電風扇相對作動形式對散熱鰭片熱阻之影響 102
5.5.1雙壓電風扇同向作動對散熱鰭片熱阻之影響 102
5.5.3雙壓電風扇水平擺放方式及相對距離之熱阻影響 104
第六章 結論及未來工作 111
參考文獻 112
個人簡歷 120
參考著作目錄 121

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