Transient coating of the inner wall of a straight tube with a viscoelastic material

We examine the pressure-driven coating of a straight tube with a viscoelastic liquid using an advanced and stable finite element algorithm, which is based on an elliptic grid generator along with local refinement and reconstruction of the mesh wherever this is needed. In particular, we investigate the case where a finite amount of viscoelastic material is allowed to deform inside a very long tube. A complete parametric analysis is performed in order to examine the effects of the elastic and inertia forces, and the various rheological parameters including the solvent to polymer viscosity ratio. Results using the exponential PTT constitutive model show that the thickness of the remaining film increases as the solvent viscosity decreases, because of the development of sharp boundary layers in the normal components of the viscoelastic stress tensor along the bubble front. In all cases the streamlines follow a 'fountain flow' pattern when the origin of the coordinate system is located at the liquid tip, due to the small effect of capillary forces. The other two constitutive models that have been examined are the FENE-CR and the Giesekus model.