微多孔塗層兩相蒸發冷卻器研究

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题名:	微多孔塗層兩相蒸發冷卻器研究
作者:	陳勁廷;Chen, Jin-Ting
贡献者:	機械工程學系
关键词:	微多孔表面;兩相冷卻;直線流道;Micro porous coating;Two Phase cooling;Straight fin channel
日期:	2018-08-14
上传时间:	2018-08-31 15:04:33 (UTC+8)
出版者:	國立中央大學
摘要:	由於電子設備的快速發展，高熱通量的散熱變得更加重要。在過去的幾十年裡，已經使用諸如空氣冷卻和液體冷卻系統等成熟技術，獲得了出色的熱管理解決方案。但是，由於熱傳係數低，它們不再是可行的解決辦法。兩相冷卻系統為更高的熱傳提供了一種可能的解決方案。若欲傳遞相同熱傳量，由於液體之潛熱遠高於顯熱，兩相冷卻所需要的流量和泵動力比單相冷卻低得多，能夠降低所需要的泵動力。一般對於池沸騰熱傳之增強，多於蒸發表面製作結構表面或多孔表面，以增加其活化孔穴數量。多孔表面則是由不同或單一尺寸之金屬顆粒，以燒結或電鍍等方式製作而成，粒子堆疊會產生孔穴以及互相連接的通道。傳統的多孔材料塗層較厚，導致加熱表面與蒸發表面之間的熱阻較大，因此多孔表面的傳熱性能下降。微孔表面可以改善這個問題，因為微孔表面全部位於過熱區域，所以更容易產生氣泡，而多孔層較薄，熱阻也較小。在本研究中，我們設計了不同直線流道大小的蒸發熱交換器，並使用平均顆粒尺寸為 20 µm 的鋁粉塗佈於蒸發冷卻器上，來比較有塗層和非塗層熱交換器的熱傳性能。實驗結果顯示微多孔表面，鰭片間距 2mm，在高熱通量時熱傳增強效果較好，與平滑表面相比，提升 17%~62%，且微多孔表面的粒子堆積會形成互相連結的通道，可幫助液體補充至加熱表面，與平滑表面相比，微多孔表面的燒乾情形會延後發生。微多孔表面，鰭片間距 1mm 因為鰭片間距較小，汽泡生成後，容易與周圍的汽泡結合。所以其熱傳增強效果比鰭片間距 2mm 時低。;Due to the rapid development of electronic equipment, dissipating heat from high heat flux sources becomes more important. For the past few decades, excellent thermal management solutions have been attained using well-established technologies such as air cooling and liquid cooling system. However, they are no longer viable solutions due to low heat transfer coefficient. Therefore, there is an increasing need for compact and high heat-flux thermal management system. Two phase cooling system offers a potential solution for higher heat transfer. Considering the same heat transfer coefficient, two-phase flow required much lower flow rate and pumping power compare to single-phase flow, as result of higher heat transfer coefficient of two phase flow. Surface structure or porous surface due to increasing the cavity and nucleation site, can enhance the pool boiling heat transfer coefficient. Porous surface is made of different or single-size metal particles, and the stack of particles will produce cavities and interconnected channels. Cavities increase the nucleation sites which generate more bubbles, while the interconnected flow paths provide fluid flow and bubble escape path. The traditional porous material coating is thick, which cause a large thermal resistance between the heating surface and the evaporation surface, therefore heat transfer performance of the porous surface decreases. Micro-porous surface can improve this problem, because micro-porous surface is all in the superheat region, it is easier to produce bubbles while the porous layer is thin, thermal resistance is also small. In this study, we designed different size of straight fin type heat exchanger and use Aluminum powder with average particle size of 20 µm, micro porous used to coating those heat exchanger to compare the heat transfer performance of coating and non-coating heat exchanger. The experimental results show that the microporous surface has a fin spacing of 2 mm. The heat transfer enhancement effect is better at high heat flux, which is 17%~62% higher than that of the smooth surface, and the particle accumulation on the microporous surface forms a channel that is mutually entangled. It helps to replenish the liquid to the heated surface, and the dry out of the microporous surface is delayed compared to the smooth surface. Microporous surface with fin spacing 1mm, because the fin spacing is small, after the bubble is generated, it is easy to combine with the surrounding bubbles. Therefore, the heat transfer enhancement effect is lower than when the fin pitch is 2 mm.
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