不同扇葉形狀之壓電風扇對加熱平板散熱之機制與研究

Cooling the Heated Plate by Piezoelectric Fans with Different Shapes

馬聖倫(Sheng-Lun Ma)

指導教授 ： 楊鏡堂

國立臺灣大學/工學院/機械工程學研究所/碩士(2016年)

https://doi.org/10.6342/NTU201602209

摘要

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。

關鍵字

壓電風扇 ； 扇葉形狀 ； 流場可視化

並列摘要

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.

並列關鍵字

piezoelectric fan ； visualization of velocity ； fan shape

參考文獻

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