Particle migration and alignment in slot coating flows of elongated particle suspensions

We analyze slot coating flows of elongated particle suspensions and investigate particle concentration and average orientation at the coated film. Shear-induced particle migration is described by the Diffusive Flux Model, and particle orientation is given by the principal direction of the particle conformation tensor. The conformation evolution and the constitutive equation for the resulting complex liquid are adapted from classical models that describe the behavior of suspensions of cylinders and fibers and polymeric solutions of almost rigid rod-like molecules. The proposed fully coupled model is applied to slot coating flows, and is solved using the DEVSS-TG/SUPG finite element method. The results show that the wet coated film is highly nonuniform. Particle concentration and orientation vary along the film thickness and are a strong function of the operating parameters of the process, such as the film thickness-to-coating gap ratio and the capillary number of the flow. (c) 2017 American Institute of Chemical Engineers AIChE J, 63: 3187-3198, 2017