表面親疏水性與毛細效應對液滴噴射過程中微流體力學行為影響之研究

Abstract

本研究計畫擬於兩年期間，針對液滴形成和噴射過程中微流體與固體之交互作用及物理現 象，運用實驗方法與理論模擬分析，進行詳細的微流體力學行為分析。為能明確分析各項物理參數 之影響，計畫中我們擬簡化液滴生成與噴射機構，採用一噴孔片透過壓電材料的形變振動，將液體 噴射而出的設計。在第一年計畫中，我們將利用數值模擬與實驗觀察來探討不同表面親疏水性、噴 口幾何尺寸以及噴孔渠道曲率對液滴噴射行為的影響。在第二年計畫中，擬透過數值模擬與實驗觀 察，探討在不同噴孔片振動位移波型、振幅及振動頻率下，噴孔表面親疏水性對連續液滴噴射行為 的影響。數值模擬部分擬採用商業化計算流體力學軟體CFD-ACE+來進行；透過邊界條件給予液固接 觸角以模擬不同親疏水性，再利用流體體積-片段線性界面重建法來做液氣界面的時變追蹤，並以連 續表面力法來考慮表面張力的效應。在實驗的部分，擬採用微電鑄技術來製作噴孔片，並在其上施 以塗層改變其表面親疏水性。透過高速攝影機來進行現象之可視化，分析不同表面親疏水性對液滴 噴射速度、液滴斷裂時間與液滴體積之影響。

This project purposes to study within a period of two years the physical phenomenon and fluid dynamics of microfluid in the droplet ejection process. Both experimental measurement and theoretical simulation would be utilized to analyze the interaction between the fluid and solid surface as well as its effect on both droplet formation and ejection process. In order to examine in detail the effects of various physical parameters on the fluid dynamics of microfluid and droplet formation, we would utilize a nozzle plate which is vibrated by a piezoelectric actuator rather than the use of printhead with complex geometry. During the phase of first year, both numerical analysis and experimental observations will be performed to examine the influence of wetting conditions on the ejection process and droplet formation. In addition, the effect of nozzle dimensions at various weting conditions on droplet ejection process will also be investigated. During the second-year project, we would examine the effect of weting conditions on continuous ejection process of drops by the nozzle plate while varying the amplitude of vibration wave form shape with time domain. Furthermore, the influence of weting conditions on droplet ejection process will also be analyzed at various frequencies of vibration of the nozzle plate. The numerical simulation tool used in this study is the CFD-ACE+ commercial software produced by CFD Research Corporation. A VOF-PLIC interface tracking method is adapted to represent the fluid domain and to track the evolution of its free boundaries while CSF mode is choosed to model interfacial physics. The nozzle plate is fabricated using electroforming process and coated to vary wetting conditions at the air-water-solid interfaces. In this study, the high speed CCD camera connected to a video recorder will be utilized to visualize the droplet ejection process and further to analyze the droplet velocity, breakup time, and droplet volume at various weting conditions.