Steady flow simulations of compressible PTFE paste extrusion under severe wall slip

In a recent article [P.D. Patil, J.J. Feng, S.G. Hatzikiriakos, Constitutive modelling and flow simulation of polytetrafluoroethylene paste extrusion, J. Non-Newtonian Fluid Mech., 139 (2006) 44–53], a rheological constitutive equation was proposed to model the flow of polytetrafluoroethylene (PTFE) paste. Steady-state flow simulations were carried out, governed by the conservation equations of mass and momentum under isothermal, incompressible conditions, and taking into account a linear slip law at the wall due to the presence of lubricant in the paste. The constitutive model was a combination of shear-thinning and shear-thickening viscosity terms, depending on a structural parameter, ξ, which obeyed a convective-transport equation.The present work re-examines the flow problem, taking into account the significant compressibility of the paste and implementing the slip law based on the consistent normal-to-the-surface unit vector. New results are shown as contours of the ξ-parameter in the flow field as well as contours of the flow type parameter, ψ, used in the model. They offer a better understanding of the flow behaviour of PTFE in flow through extrusion dies.