兩相同心圓管流常作為了解一些實際流動程序的簡單模型。這些程序包含了原油運送、二次採油以及呼吸道阻塞。而界面活性劑的存在對於同心圓管流界面動態的影響扮演關鍵的角色。

　　本篇研究的重點在以實驗的方法探討界面活性劑對於兩相同心圓管流之界面動態的影響，並比較系統在有壓力和無壓力驅動的條件下界面動態之差別。系統主要由附著在毛細管壁上的矽油以及流經毛細管中央的水所組成。界面會因毛細不穩定效應的影響而成長，且矽油會將水阻隔，形成液體栓塞。我們測量在不同界面活性劑濃度下液體栓塞所需時間以及界面最初成長速率。實驗結果顯示相對於沒有界面活性劑存在的系統，界面活性劑的存在會增加液體栓塞所需時間以及減少界面最初成長速率。界面活性劑的影響不單只有降低界面張力，同時也有馬倫哥尼效應的產生。對於特定一個濃度的情形之下，在有壓力驅動的同心圓管流與比沒有壓力驅動的情況比較時，其液體栓塞所需時間較短，顯示施加流動有助於界面的成長。最後使用尺度分析的方法來判別我們系統裡的主導機制，同時解釋實驗的結果。

　A two-fluid core-annular flow (CAF) is of interest in variety of contexts for modeling processes such as those occurring in enhanced oil recovery and pulmonary airway closure. The presence of surface-active agents or surfactants often plays a critical role in affecting the dynamics of these processes.

　The aim of this study is to experimentally examine how surfactant affects the interfacial dynamics of a pressure-driven CAF. The system is established in a capillary that consists of the water core surrounded by the oil annulus. The interface amplifies due to the capillary instability and could snap the core off, leading to liquid blockages. Snap-off times and initial growth rates are measured for different concentrations of surfactant. Experimental results show that the surfactant increases the snap-off times and slows down the initial growth rates compared with the surfactant-free case. These surfactant effects are not due to lowering interfacial tensions, but rather to interfacial-tension-gradient forces, i.e., Marangoni effects. For a given surfactant concentration, a pressure-driven CAF has a shorter snap-off time than no-imposed-flow, suggesting that an imposition of flow is prone to promoting the growth of the interface. Scaling analysis is used to identify the dominant mechanisms as well as to explain our experimental results.

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