• 作者： Yang, Chen-Jen; Maa, Jer-Ru; Yang, Yu-Min
• 中文摘要： 液層表面的蒸發會造成表面張力梯度,產生自然對流。此一效應在較薄的液層或急劇蒸發的系統中非常重要。如果液體中含有微量的界面活性劑,則會抑制此一效應,使得蒸發速率顯著地降低。本文由一套可以直接測量蒸發速率的實驗裝置,研究界面活性劑(sodium lauryl sulfate、 stearic acid)的添加與否對水的蒸發速率的影響,並探討表面張力驅動與浮力驅動自然對流在蒸發過程中的相對重要性。實驗結果顯示,在液層高度為1公分時,上述兩種成因的自然對流大約具有相等的影響力。界面活性添加劑的影響則歸因於汽-液界面的彈性本質。
• 英文摘要： Natural convection can be induced by surface tension gradient due to uneven evaporative cooling at the surface of a liquid layer. This effect is important when the liquid layer is thin or the evaporation rate is fast, and it can be inhibited. The evaporation rate is reduced considerably if a small amount of surfactant is added to the liquid. In this work, an evaporation chamber containing superheated water is designed to measure the evaporation rate directly by counting the condensate drops dripping from the conical roof of the chamber. Relative importance of the surface tension-driven and buoyancy-driven natural convection is studied by comparing the evaporation rates before and after the addition of the surfactant. The surfactants used in this work are sodium lauryl sulfate and stearic acid. Experimental results indicate that these two modes of natural convection are about the same magnitude as the liquid depth is reduced to 1cm. The reduction of evaporation rate by the addition of surfactant is ascribed to the elastic behavior of the vapor-liquid interface.
• 中文關鍵字： 蒸發對流; 界面現象; 過熱水; 界面活性劑; 表面張力
• 英文關鍵字： Evaporative Convection; Interfacial Phenomena; Superheated Water; Surfactant; Surface Tension