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In the present paper, the viscoelastic flow through an asymmetric planar contraction geometry inside slot die was studied experimentally. The velocity field in the geometry was measured by particle image velocimetry (PIV), and the statistical characteristics of the entrance flow were evaluated. It was found that the entrance flow attached to the side wall on the contraction and the flow around the lip wall became unstable, which were due to the viscoelastic effect of the fluid. This resulted into the vortex formation on the corner of the contraction at large Weissenberg number Wi > 30 in the Reynolds number Re < 7. It is concluded that the entrance flow can be categorized into Newtonian-like flow region, transitional region, and the vortex formation region in the geometry.

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In this work, entrance flows of viscoelastic fluids from a cavity to a slot in a slot die coating were investigated experimentally and numerically. Aqueous solutions of polyethylene glycol (PEG) and polyethylene oxide (PEO) mixtures, having viscoelasticity and Newtonian viscosity, were tested in order to clarify the effects of viscoelastic characteristics to the excess pressure drops at the entrance. The measured excess pressure drop changes corresponded to the flow pattern changes from a Newtonian-like flow pattern to vortex generation and growth patterns in an asymmetric entrance flow with a submillimeter slot. Numerical predictions of the transitions in the flow patterns and the pressure drops were also made utilizing exponential Phan-Thien-Tanner (EPTT) model with a finite element method. The predictions qualitatively indicated the increase in excess pressure drop and the vortex generation and growth.

In this study, the fast numerical computation method by using simplified momentum equations, which exactly clarified the flow state inside a slot die, was developed, in order to obtain higher coating quality. The computation results elucidated the dependence of the uniformity of coating thickness on non-Newtonian characteristics. In addition, it was found that the computational procedure enables us to seek the optimum internal figures of a slot die immediately. The method was extended to a variety of rheological models, such as Power-Law, Ellis and Hershel-Bulkley model. As a result, the computation technique industrially contributed to the development of precise coating productions, such as optical elements, semiconductor and LCD display components.