Instability of the Flow in a Closed Cylindrical Cavity and in a Short-Dwell Cavity, 1999 Coating Conference Proceedings

S. Mourad

S. Skali-Lami

LEMTA

C. Trehoult

Centre Technique du Papier

The short-dwell coating process was largely studied some years ago. These studies were carried out to understand streak phenomenon that appears on the deposited film. The link between these imperfections and hydrodynamic instability have already been demonstrated. On the other hand the link between hydrodynamic instability, the dimension of the cavity and the rheological properties of the coating colors are not yet established.

In the objective of a best knowledge the effects of the size of cavity and the non-Newtonian behavior of coating color on these instabilities were investigated. Simulations have been carried out in 3D, As opposed to those previously carried out in 2D they give more detail on steps of the destabilization of the flow. The influence of non-Newtonian color behavior on this instability has also been analyzed. A critical generalized Reynolds number is defined.