A study of various factors affecting Newtonian extrudate swell

Abstract

Finite-element simulations have been undertaken for the benchmark problem of extrudate swell present in extrusion. Both cases of planar and axisymmetric domains were considered under laminar, isothermal, steady-state conditions for Newtonian fluids. The effects of inertia, gravity, compressibility, pressure-dependence of the viscosity, slip at the wall, and surface tension are all considered individually in parametric studies covering a wide range of the relevant parameters. The present results extend previous ones regarding the shape of the extrudate and in particular the swelling ratio. In addition, the excess pressure losses in the system (exit correction) were computed. The effect of the domain length is also studied and is found to be of importance in all cases, except for slip and surface tension effects. The effect of the extrudate length is particularly important for inertia and gravity flows. Inertia reduces the swelling down to the asymptotic theoretical values at infinite Reynolds numbers. Gravity acting in the direction of flow also reduces exponentially the swelling. When the flow is creeping and gravity is zero, surface tension, slip at the wall, and pressure-dependence of viscosity, all decrease the swelling monotonically, while compressibility increases it after a small initial reduction. The exit correction decreases monotonically with inertia, gravity, and slip, increases monotonically with compressibility and pressure-dependence of the viscosity, and is not affected by surface tension. © 2011 Elsevier Ltd.