請用此 Handle URI 來引用此文件:
http://tdr.lib.ntu.edu.tw/jspui/handle/123456789/28341
標題: | 奈米粒子薄膜疊層組裝於池沸騰熱傳增強研究 Enhanced Pool Boiling Heat Transfer Using Layer-by-layer Assembly of Nanoparticulate Thin Film |
作者: | Dong-Fu Chen 陳東孚 |
指導教授: | 陳瑤明 |
關鍵字: | 疊層組裝,親疏水表面,池沸騰,熱傳增強表面, Heat transfer enhancement,Pool boiling,Thin-film coating, |
出版年 : | 2011 |
學位: | 碩士 |
摘要: | 各種表面改質技術已運用於醫學、生活與機械等領域。其中,在熱傳的研究上,應用其方法改變接觸角大小,探討對熱傳之影響為值得研究之方向。本研究旨在以二氧化矽奈米粒子之疊層組裝於銅塊表面上進行親、疏水性之改質,以池沸騰系統探討親、疏水特性對熱傳之影響。
以水與99.5% 酒精作為改質效果評估之工質,由測量結果發現,經改質之銅塊,可使表面更親水,水的接觸角由未改質的87°變為43°,也可更疏水(134°)。酒精於未改質表面上接觸角為14°,與在親水性表面上相比(<10°)差異不大,但於疏水表面則有明顯變化(45°);且相較於未改質表面,親水表面有助酒精的擴散及蒸發速度,而疏水表面則是聚為一個不會擴散之液滴。 水與酒精的熱傳研究結果都顯示親水改質主要的提升反應在臨界熱通量上,而疏水改質則會提升熱傳係數。特別注意的是水於低熱通量(約50 kW/m2)時,即會發生表面乾涸之現象,不利於熱傳。而酒精的實驗中,可發現,親水與未改質表面由於角度變化不大,因此熱傳結果也相似。對高濕潤性工質而言,改質應以疏水表面為主,以提升熱傳性能。 The purpose of this research is to enhance the boiling heat transfer capacity in a pool boiling system by changing surface wettability using layer-by-layer (LbL) assembly method, which was applied to a copper surface. To observe the effect of the wettability, the present study measured the contact angle of water and 99.5% ethanol on the plain surface. After coating process, the contact angle of water varied from 43° to 134°. The contact angle of ethanol is 14° on the uncoated surface and 45° on the hydrophobic, respectively. On the hydrophilic surface, however, the contact angle is below 10°. In contrast with the uncoated surface, the ethanol spread and then evaporated fast on the hydrophilic surface. However, it became a liquid droplet on the hydrophobic surface. In the pool boiling experiments using water and ethanol, for the hydrophilic surface, it was found that the critical heat flux would be enhanced, and the heat transfer coefficient would be promoted on the hydrophobic surface. Moreover, hydrophobic surfaces became vapor-blanketed at 50 kW/m2 using water as working fluid. It indicated that the hydrophobic surface would decrease the heat transfer coefficient at low heat flux. The heat transfer characteristics during the boiling process of ethanol on the uncoated surface and on the hydrophilic surface were similar. For a high wettable liquid, hydrophilic surface would not affect the boiling heat transfer. The results in the present work suggested that using hydrophobic surface for a heat transfer enhancement. |
URI: | http://tdr.lib.ntu.edu.tw/jspui/handle/123456789/28341 |
全文授權: | 有償授權 |
顯示於系所單位: | 機械工程學系 |
文件中的檔案:
檔案 | 大小 | 格式 | |
---|---|---|---|
ntu-100-1.pdf 目前未授權公開取用 | 2.83 MB | Adobe PDF |
系統中的文件,除了特別指名其著作權條款之外,均受到著作權保護,並且保留所有的權利。