圓柱形腔體內部散熱鰭片與機械震盪結合之自然對流研究

Abstract

自1970年代石油危機開始，世界各國慢慢注意到發展再生能源的必要性，以減緩對石油等傳統能源的依賴，如太陽能、風力、地熱以及波浪能等等。這些大自然的能源可謂取之不盡，用之不竭。

近年來台灣在這方面發展也逐漸步上軌道，本文的實驗原型是來自工業技術研究院20 kW等級之波浪發電機組，因波浪發電機組內含大量電子零件，而機組本身是完全封閉之腔體，散熱就變成一大課題。

本研究的目的在以實驗的方法探討類似波浪發電機組內部的圓柱形中空腔體，模擬波浪發電機組內部發熱源，並以步進馬達以及震盪機構模擬波浪發電機組在海面上載浮載沉的運轉條件，探討腔體震盪對自然對流熱傳的影響，研究不同的腔體高度(H=2.5cm,5cm)、震盪頻率(f=1Hz,2Hz)、Rayleigh number(Ra=5×〖10〗^4~6×〖10〗^5)以及散熱鰭片對自然對流的影響。經由實驗得到的結果可看出，因震盪而增加熱傳的效果(E_v (Nu)，為1.0~1.1)明顯比因加入散熱鰭片而增加的熱傳(E_f (Nu)，為1.1~1.4)還少，因此可判斷在此震盪條件下，腔體內部的自然對流受到震盪因素影響的程度是不明顯的。

Since the energy crisis in 1970s, the attention in developing renewable energy such as solar energy, wind energy, geothermal energy and wave energy has increased worldwide in order to reduce the dependence on traditional energy. In the recent years, the development of the renewable energy industry in Taiwan has matured gradually. The prototype of the experiment in this study is a 20 kW class wave energy converter (WEC) from Industrial Technology Research Institute (ITRI). Because of large amount of electronic equipment in WEC chamber, the heat dissipation becomes an issue due to the sealed chamber. This study aims to investigate the natural convection associated with mechanical vibrations and pin fins in a cylindrical cavity with the heated surface facing upward. The mechanical vibration is produced by a stepper motor and an oscillation mechanism to simulate the operating condition of the WECs in the sea. The experimental parameters include different cavity height (H=2.5cm, 5cm), vibrational frequency (f=1Hz, 2Hz), and Rayleigh number (Ra=5×〖10〗^4~6×〖10〗^5). According to the results of the present study, the heat transfer enhancement as a result of mechanical vibrations (E_v (Nu), 1.0~1.1) is less than that of finned cases (E_f (Nu), 1.1~1.4).