奈米碳管印製於紅銅圓柱表面之冷凝熱傳研究

Abstract

本研究探討在密閉腔體下的冷凝熱傳現象。以外直徑25mm的紅銅館為熱傳導物質，利用較為簡單的印製方式在紅銅柱表面印上奈米碳管墨，以不同印製面積比當作變因，也就是比較純紅銅、全冷凝表面印製、30%、50%、70%，進行實驗觀測該印製的奈米碳管對於冷凝現象的影像。 經量測顯示奈米碳管印製面積的接觸角為76∘，而未改質表面之接觸角為107∘，然而實驗結果觀測到，在低過冷度段，也就是0~7.5∘，印製面積30%和50%均有呈現熱傳增強的現象，經影像觀測發現在此過冷度區間不分親水性面積有助於冷凝液的移動和成核。而過冷度大於7.5∘，也就是近濕潤轉變後，印製面積30%、50%、70%的熱傳效果有降低的趨勢。由此研究可得知，此方法印製的奈米碳管表面會呈現親水性，但部分印製的冷凝表面再低過冷度區間有熱傳增強的效果。

This research focused on condensation heat transfer of copper cylinder inside a closed chamber. The dimension of cylinder is 25mm in diameter and 50mm in length. Besides, the modification method is printing carbon nanotube (CNT) onto the copper surface with different printing area ratio: 0%, 30%, 50%, 70%, and 100% as one of controlling factors. The other one is the subcooling degree, which is the temperature difference between condensation wall and steam. After measurement, the wettability of CNT printed area is hydrophilic, while the one of plain surface is hydrophobic. However, the experimental results showed that within lower interval of subcooling degrees, which is 0 to 7.5∘, the heat transfer coefficient and heat flux of the 30% and the 50% types are higher than the plain one. Accompanying the experimental images, hydrophilic surface has benefit to droplet movement and nucleation. On the other hands, the 30%, the 50%, and the 70% types worsen the heat transfer as the subcooling degree is >7.5∘ because the wetting transition induced the flooding upon the surface. From this research, even with hydrophilic patterns, the heat transfer performance could be enhanced during some subcooling degrees.