本研究利用微機電製程中的黃光微影技術配合十二烷硫醇表面改質技術，製作出表面自由能梯度的表面。不同表面自由能梯度表面的冷凝板，配合本研究所設計的冷凝實驗系統，探討各種冷凝板之熱傳效率。本研究目的為利用表面自由能梯度具有驅動液滴的機制，以達到提升冷凝熱傳的效率。並以理論推導出液滴在垂直表面上移動前的最大尺寸。
本研究使用矽晶片(wafer)作為冷凝板之基材，在矽晶片表面上製作出不同的黃金梯度表面，經過十二烷硫醇改質後，便能產生各種不同表面自由能梯度的冷凝板。上述之梯度冷凝板及親、疏水均質的冷凝板經過本研究所設計之冷凝系統量測其熱通量後，發現梯度表面中具有比較好熱傳效率的冷凝板，會比全親水表面冷凝板的熱傳效果約高出10％，表示本研究所設計之梯度表面對於冷凝熱傳量的確有提升的效果。在均質冷凝板的部份，疏水表面會比親水表面有較好的熱傳效果，且冷凝腔體中的壓力不會影響此結果。液滴移動前最大尺寸的理論推導結果，與本實驗所觀察到的結果相近，也顯示出表面張力能有效影響液滴移動的範圍。藉由此研究的結果，相信對於未來冷凝熱傳的領域能有所幫助。

This research studies the improvement of condensation heat transfer efficiency on a free energy gradient condensation surface. Different from previous studies, the condensation surface is fabricated by using photolithography technique, as well as 1-Dodecaneethoil self-assembly monolayer (SAM) surface modification technique. To test gradient condensation surface, a vertical condensation system is designed in this study. Different gradient condensation surfaces, as well hydrophilic and hydrophobic surfaces, are investigated their condensation heat transfer efficiency by directly measuring the heat flux in the system. Experimental results find that the gradient condensation surface with contact angle gradient dθ/dx=? degree/mm has the best performance above all the surfaces. Its heat transfer efficiency can be 10% higher than the pure silicon hydrophilic surface. The mechanism for the optimal contact angle gradient is also studied by both theoretical and experimental methods. A theoretical analysis is performed to estimate the minimum droplet size that can move on a vertical gradient surface. It finds a good agreement between the theoretical prediction and the experimental results. This verifies the theoretical model can well explain the physics behind the current research. Based on the theoretical model, a length scale L, defined as where r,  and g represent the liquid surface tension coefficient, liquid density and gravity, is found. When the gradient surface length scale C is much higher than the length scale L, the system can be considered as an only gravity driven system. Droplet size that will move on the vertical surface is controlled by the balance between the gravity force and contact angle hysteresis force. When the length scale C of the gradient surface is smaller than the length scale L, the surface tension gradient driven force start to show effects. It is found that C=1mm gradient surface can cause smaller droplets to moveand it is believed this is the major mechanism responsible for the better heat transfer effiency.

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