Visualization and modeling of flow inside gravure cells and grooves.

摘要

Gravure coating and printing are processes that can produce thin films and tiny patterns on solid substrates in a continuous manner by using a cylinder patterned with grooves or cells. This thesis investigates the flow inside individual gravure groove and cell by exploiting flow visualization, lubrication-approximation-based analysis and theoretical modeling by Galerkin/finite-element solution of an elastohydrodynamic equation system.; For flow visualization, the emptying process is initiated by moving over a scaled-up groove or cell a rotating roller or a glass top with a curved surface. For the scaled-up groove, a region of recirculating flow is observed to attach to the moving glass top. For the scaled-up cell, an air bubble may appear inside the cell when the minimum gap between the glass top and the cell is zero, and a liquid bridge is observed when this gap is positive. The amount of liquid remaining in the cell, Vr, is measured for different liquids, surface speeds, surface deformabilities and gap distances for both the glass top and the rotating roller. For each liquid, Vr increases as the speed of the glass top or roller increases. The data are correlated by multiplying Vr by a liquid-dependent shift factor, which leads to a power-law relationship between the shifted Vr and the capillary number.; A lubrication-approximation-based model is developed to study the elastohydrodynamic interactions between flow over a rigid cavity and a flexible wall. The pressure profiles are dramatically altered by the deformation of the wall. The cavity shape is found to have a significant influence on both the pressure profiles and the wall deformation.; A two-dimensional model is developed to verify the applicability of the lubrication model. The results indicate that the lubrication model can predict pressure profiles qualitatively, and positions of the flexible wall and flowrate quantitatively. This model is also used to study the flow between a rigid wall and a cavity with a flexible bottom, which is subject to an outside pressure. As the outside pressure changes, the position of the stagnation streamline, which prohibits liquid to transport from the recirculation regions to the surrounding flow, may be changed.