不同歐式數和黏度比下液柱斷裂現象之研究

Abstract

柱斷裂是整個工業和自然界中普遍存在的過程，在工業應用上需要生產大量相同尺寸的液滴，同時也要避免產生較小的衛星液滴或其他殘餘流體，所以微流體技術的應用引起了極大的關注，特別是在控制生成均勻大小的液滴並將其構建成模塊方面。為了改進這些技術，關鍵在於了解液柱斷裂的物理機制，而機制主要分成慣性政權、黏性政權和慣性-黏性政權。由於實驗設備的限制，對於光學尺度下的解析度而言微米等級已經是極限，故無法更好解析更細薄時的情況，因此使用開源的模擬軟體 ( GERRIS ) 來研究液柱收縮之機制是非常具有潛力的，探討不同Oh數下的液柱斷裂現象，並調整外內黏性比例來探討黏滯性差異所造成的影響。結果表明，微黏性流動：只有當外部黏度大於內部黏度時才會影響斷裂過程。一般情況下，斷裂過程不受外部黏性的顯著影響。低黏性流動：當外部黏度達到一定程度（m = 0.4）時，即開始影響液柱自相似收縮。黏性比大於1時，外部黏性影響加劇，導致新的相似性。中黏性流動：外部黏度稍大即影響收縮過程。黏性比等於1時，抑制擾動進入穩定階段。黏性比大於1時，斷裂過程完全由外部黏性控制，出現新的相似性。高黏性流動：外部黏性稍大即影響收縮過程。黏性比等於1時，觀察到趨勢但理論無法證明。黏性比大於1時，外部黏性過強導致液柱無法斷裂，表面演化不同於其他黏性流動。 環境對液柱斷裂所造成的影響，隨著內部黏性提升，影響也越明顯，且影響的液柱半徑尺度也越來越大。由這些研究成果對於連續噴墨的印刷技術、三維3D列印機或藥物打印等相關領域，在工業應用上有莫大的幫助。

The breaking of liquid columns is a common process in both industry and nature. In industrial applications, it is important to produce droplets of the same size while avoiding the creation of smaller satellite droplets or other residual fluids. Therefore, the application of microfluidics has garnered significant attention, especially in the control and construction of uniformly sized droplets. To improve these techniques, it is crucial to understand the physical mechanisms of liquid column breakup, which can be divided into inertial, viscous, and inertia-viscous regimes. Due to limitations in experimental equipment, the resolution at the optical scale has reached the micron level, making it difficult to analyze thinner situations. Thus, using open-source simulation software (GERRIS) to study the mechanism of liquid column contraction has great potential. The study investigates the breakup phenomenon of liquid columns at different Oh numbers and adjusts the internal and external viscosity ratios to explore the impact of viscosity differences. The results indicate: Micro-viscous flow: Only when the external viscosity is greater than the internal viscosity does it affect the breakup process. Generally, the breakup process is not significantly affected by external viscosity. Low-viscosity flow: When the external viscosity reaches a certain level (m = 0.4), it begins to affect the self-similar contraction of the liquid column. When the viscosity ratio is greater than 1, the influence of external viscosity increases, resulting in new similarities. Medium-viscosity flow: A slight increase in external viscosity affects the contraction process. When the viscosity ratio is equal to 1, it suppresses disturbances and enters a stable phase. When the viscosity ratio is greater than 1, the breakup process is completely controlled by external viscosity, resulting in new similarities. High-viscosity flow: A slight increase in external viscosity affects the contraction process. When the viscosity ratio is equal to 1, a trend is observed, but theory cannot prove it. When the viscosity ratio is greater than 1, the external viscosity is too strong, preventing the liquid column from breaking. The surface evolution is different from other viscosity flows. The impact of the environment on the breakup of liquid columns becomes more pronounced as the internal viscosity increases, and the affected radius scale of the liquid column also increases. These research findings are highly beneficial for industrial applications in fields such as continuous inkjet printing, 3D printing, and drug printing.