奈米結構於微流道表面之池沸騰熱傳影響研究

彭紳泰(Shen-tai Peng)

指導教授 ： 楊建裕

國立中央大學/工學院/機械工程學系/碩士(2014年)

摘要

本研究以甲醇為工作流體在一大氣壓下進行實驗探討奈米結構於微流道表面之池沸騰熱傳影響，實驗結果分為平滑表面、微流道表面、奈米結構於微流道表面之池沸騰熱傳，共三部份做探討。其中微流道表面以及微流道表面有奈米結構之探討參數則分為不同流道寬度(300 µm V.S. 400 µm)及不同鰭片寬度(300 µm V.S. 400 µm)進行探討。
於微流道表面之池沸騰熱傳實驗結果顯示流道寬度越寬，熱傳效果越好，因微流道表面之汽泡生長尺寸與流道寬度成正比。於探討微流道表面不同鰭片寬度於池沸騰熱傳之影響的實驗結果顯示鰭片寬度越寬，熱傳效果越好，因相鄰兩流道間產生的汽泡相聚合形成聯合汽泡的可能性隨鰭片寬度減小而增加，使熱傳能力降低。
微流道表面於低熱通量之熱傳增強主要依靠相較於平滑表面有較大尺寸成核孔洞於相同壁面過熱度下成為活化孔洞使熱傳增加，於高熱通量時則因為平滑表面之成核孔洞皆已活化使微流道表面與平滑表面之熱傳能力相差甚小。
微流道表面有奈米結構之池沸騰熱傳實驗結果顯示因奈米結構能改變工作流體接觸角使其從親水轉變為疏水，使奈米結構於微流道表面之實驗相較於微流道表面能於相同壁面過熱度的情況下，具有更多活化孔洞產生更多汽泡，使研究結果相較於微流道表面無奈米結構之結果的熱傳能力更為提升，並且於探討不同流道與鰭片寬度時之趨勢與微流道表面之趨勢一致(流道與鰭片寬度越寬越好)，但活化孔洞越多則越容易形成聯合汽泡，使乾涸現象相較於微流道表面在較低熱通量時發生。

關鍵字

奈米結構表面 ； 微流道表面 ； 流道寬度 ； 鰭片寬度 ； 池沸騰熱傳

並列摘要

In this research work, saturated pool boiling experiment is carried out to study the effect of Nanostructure on silicon microchannel surface. Methanol is used as working fluid at atmospheric pressure. Mainly three types of surface was prepared, namely, Plain surface, surface with microchannel and nanostructured microchannel surface. The effect of micro channel width (300 µm & 400 µm) and fin width (300 µm & 400 µm) are studied on both surface.
The experimental results shows at lower heat flux, wider micro channel performs better in terms of enhancing heat transfer coefficient. Because the bubble diameter is bigger in wider channel. In the case of fin width, thicker fin performs better at lower heat flux because the probability of bubble coalesce between neighbor channels is less and as a result of that bubble departure frequency is higher.
With respect to plain surface, microchannel surface has larger size cavities, so at given low heat flux, it has more active nucleation sites. Where as in higher heat flux there is not much heat transfer enhancement on microchannel surface, since nucleation sites on flate surface are active.
Nanostructured micro channel surface has higher contact angle. As a result of that at a given heat flux, the number of nucleation sites is more. So the pool boiling heat transfer enhancement is better compare to microchannel without nanostructure surface. Similar enhancement trend has been observed while in comparing the effect of fin width and microchannel width. The CHF of nanostructured surface is lower because hither nucleation site density result in more bubble coalesce and dry out.
Key word: Nanostructure surface, microchannel surface, fin width, channel width, pool boiling heat transfer.

參考文獻

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