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A mathematical model for the dip coating process has been developed for cylindrical geometries with non-Newtonian fluids. This investigation explores the effects of the substrate radius and hydrodynamic behavior of the non-Newtonian viscous fluid on the resulting thin film on the substrate. The coating fluid studied, Dymax 1186-MT, is a resin for fiber optics and used as a matrix to suspend 1 vol. % titanium dioxide particles. The coating substrate is a 100 μm diameter fiber optic diffuser. Ellis viscosity model is applied as a non-Newtonian viscous model for coating thickness prediction, including the influence of viscosity in low shear rates that occurs near the surface of the withdrawal film. In addition, the results of the Newtonian and power law models are compared with the Ellis model outcomes. The rheological properties and surface tension of fluids were analyzed and applied in the models and a good agreement between experimental and analytical solutions was obtained for Ellis model.

This study deals with the numerical simulation of free-surface concentrated suspensions using the finite volume method. The numerical procedure, based on the particle diffusion-flux model, is implemented in a computational fluid dynamic platform for estimating the particle volume fraction in three-dimensional flows with arbitrary geometry and boundary conditions. The Volume of Fluid (VOF) method has been applied to track the flow interface between liquid and gas, with the solid particles dispersed in the liquid phase, in the free coating process. A finite length cylinder is dip coated, where the substrate is pulled out of a concentrated suspension bath. In the current work, the initial solid particle volume fraction range is 0.1-0.4 and the withdrawal velocity varies in the range of 0.05-0.15 m/s. Comparisons are made between numerical simulation predictions and experimental results for coating layer thickness, with close agreement achieved.

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