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1 2010

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Numerical simulation of blade-over-roll coating forming flows

Mitsoulis E., Athanasopoulos G.

Computer Methods in Materials Science

2010

Vol. 10, No. 4

214-224

Numerical simulations have been carried out via the finite element method (FEM) for the forming flow of coating using a system of blade and roli. The flow domain encompasses both the coating fluid reservoir and the doctor-blade region with free surface and is fully two-dimensional. The materials of this study are Newtonian and shear-thinning polymer solutions used previously in an experimental and theoretical investigation. The pseudoplasticity of the polymeric liquids is modelled by the Carreau model, which fits well experimental data for the shear viscosities. For different roll speeds, the entire flow domain is analyzed, and the extent and shape of recirculating zones are found. Large vortices appear in the reservoir, and their intensity is computed under different operating conditions and blade geometries. The computed free surface profiles and coating thicknesses arę in close agreement with the experimental ones. Shear thinning increases the coating thickness for a given geometry, as was also found experimentally, when compared with the Newtonian values. This increase is valid up to power-law index n great than 0.3, while extreme shear-thinning (power-law index n less than 0.3) reduces the coating thickness. This new finding is in agreement with previous findings in other geometries for highly shear-thinning fluids. The vortex decreases in size and intensity monotonically and linearly with n, in the range 1 greater-than or equal to n greater than 0. The simulations also provide a wealth of information regarding stresses and pressures and show that some geometries are better than others in coating operations. The flow geometry provides an interesting case for simulation and design, due to a combination of fluid mechanics and shear-thinning phenomena that take place in this flow field.