Investigation of Coating Liquid Layer Behaviour at Curved Solid Edges

In our study we examined the behaviour of thin liquid layers at curved solid edges experimentally and numerically by coating investigations based on the laser-induced fluorescence technique (LIF) and by numerical film simulations based on the Volume-of-Fluid multiphase flow model (VOF), respectively. The main motivation was to find optimal combinations of influencing quantities to reduce the so-called Fat-Edge effect. Therefore, we performed a study of these influencing quantities, in which application parameters like edge curvature radii of the solid substrates and application layer thicknesses as well as determining liquid properties like viscosity and surface tension have been varied. Results are described qualitatively at corresponding Fat-Edge shapes and quantified by suitable Fat-Edge parameters, which had to be identified and selected.We can show that adverse and appropriate influencing parameter combinations exist, which generate conspicuous and less distinctive Fat-Edges, respectively. The experimental findings and proportionalities regarding Fat-Edge shapes and dimensions are found to be physically plausible. Furthermore, an order of significance of the influencing quantities has been established.Eventually, we could derive a dimensionless quantity by dimensional analysis, which describes the Fat-Edge effect. Thus, the Fat-Edge effect may also be described by the application of similarity theory and a corresponding dimensionless number.