Analysis of extrudate swell from an annular die
The annular die extrusion with the jet swell problem belonging to it is treated numerically using a control volume finite difference scheme which was developed previously for the treatment of the capillary and slit jet swell problem by other authors referred to in the quoted literature. In consequence of the annularity of the die there exist different inner and outer boundary shapes of the jet and therefore the problem is not a pure symmetrical one. Hence it results a remarkable amount of equations to be solved. The governing equations such as momentum and continuity equations and the boundary conditions such as the no-slip condition at the walls of the die and the no-shear stress condition at the free surfaces, for instance, at first are set up using physical coordinates and then are transformed into expressions more suitable for the numerical computation process. The governing parameters of the problem are derived. Newtonian and non- Newtonian fluids, especially so-called power-law fluids with respect to the viscosity distribution are considered. From the numerical and the physical points of view the following items are discussed thoroughly: Grid and control volumes, conservation equation for the control volume, effect of mesh refinement, the stick-slip problem for an annular die, jet swell in the absence of gravity and surface tension, effect of gravity, acting in the longitudinal direction, effect of surface tension, effect of power-law index, effect of die gap, including the limiting cases of capillary and slit die.
scientific article; zbMATH DE number 92733