Theoretical Analysis of Low-Capillary Number Dip-Coating Processes

• Main Authors: Chih-Jen Hsueh, 薛智仁
• Other Authors: 賴君亮
• Format: Others
• Language: en_US
• Published: 2007
• Online Access: http://ndltd.ncl.edu.tw/handle/35729289907429359341

碩士 === 臺灣大學 === 機械工程學研究所 === 96 === The present study is aimed at investigating theoretically the dip-coating processes. Based on the appropriate scaling analysis, three flow regimes are defined; they are the low-capillary number flows, the viscocapillary flows, and the high-capillary number flows. The whole flow domain is further decomposed into three regions with specific flow characteristics; they are Region I, the constant-thickness region, Region II, the nearly one-dimensional dynamic region, and Region III, the static region. Numerical calculations using the fifth-order Runge-Kutta- Fehlberg method are needed for the dynamic region, which is then matched smoothly to Region I and III to give the solution for the whole flow domain. The results indicate that the liquid film is reduced when the gravity effect becomes important or the value of To increases. Thus, in micro-gravity environment, a larger distance is necessary to attain a uniform thickness of coating material on the substrate when the dip-coating process is applied. In addition, with stronger surface tension or a smaller value of Ca the free surface of the liquid film becomes more concave and, consequently, the length of the liquid film before reaching the constant-thickness region, L, increases.