目前高功率LED在應用上難免會遇到熱的問題，熱效應不僅會影響LED的發光效率及其使用的壽命，還會改變其發射波長。且一般LED在小區域內擁有1W的熱量，對於一般傳導、強制空冷及熱電元件等方法的散熱片而言，熱量並沒有辦法有效的傳出，因此藉由熱管內流體的兩相轉換去達到熱擴散的效果，進而降低LED的junction temperature。但目前市售的圓柱狀熱管對於平面熱源會遇到接觸上的問題，而平板式熱管的優點就是可以降低與熱源的接觸熱阻，使得熱量得到良好的傳遞。且平面式熱管在內部工作流體的使用上，不僅可以增加內部流體的填充量，並應用多條流道增加流體回流量。 本實驗製作出輻射狀及平行流道兩種不同流道形式的熱管，去觀察其產生的熱擴散效果的差異性。熱源置中的輻射狀結構之平版式熱管，利用蒸汽流將熱量從中央擴散至兩側，達到熱擴散的效果。但是實際上熱管並沒有作動的效果，主要是熱管的溫度受控於面積較大的冷卻端溫度，使得熱管內部的工作流體無法到達沸騰的工作溫度。而平行流道的熱管，是由一端加熱汽化後將熱量帶至另一端進行冷卻，進而提升散熱面積。由實驗可知在冷熱端分開的狀況下，皆有沸騰的現象產生，而填充量30％時沸騰後所降低的熱阻值比填充量63％來的高，且較不受限於熱管的擺放角度。The high power LED possesses of high brightness, environmental protection, and energy saving. But owing to the heat effect, this LED would be reduced life time and efficiency, and result in the wavelength shift. The general heat sink cannot diffuse heat effectively for the small size LED. Therefore, using the main characteristic of two-phase changed of heat pipe can achieve the heat diffusion and reduce the junction temperature of LED. The cylinder heat pipe is not convenient for contacting with the flat heat source. Thus flat heat pipe is used to increase contact area and to decrease the contact resistance between heat source and heat pipe. The flat heat pipes not only increase the fill of working fluid, but also use more grooves to transport liquid back to hot point. In this case, we fabricated different shape grooves flat heat pipes, radial grooves heat pipe and parallel grooves heat pipe, to observe the heat transportation of heat pipes. The heat transfer of radial heat pipe starts from the center to edge by vaporizing working fluid to enhance diffusing area. But the radial heat pipe has no significant effect in reducing the temperature of heat source. The main reason is that the temperature of heat pipe is controlled by cold point, thus the working fluid cannot boil. The heat transport of parallel heat pipe starts from edge to edge, so that the diffusion area of parallel heat pipe can be enlarged. In parallel case, the working fluid can boil under different liquid fills and incline angles, thus the thermal resistance is reduced effectively. The reducing thermal resistance of 30% fill is better than 63% fill, and 30% fill is no limited by gravity force.
