Journal of Non-Newtonian Fluid Mechanics, Vol.157, No.1-2, 26-33, 2009
Steady flow simulations of compressible PTFE paste extrusion under severe wall slip
In a recent article [P.D. Patil, J.J. Feng, S.C. 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, xi, 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 xi-parameter in the flow field as well as contours of the flow type parameter. psi, used in the model. They offer a better understanding of the flow behaviour of PTFE in now through extrusion dies. (C) 2008 Elsevier B.V. All rights reserved.
Keywords:Polytetrafluoroethylene;Axisymmetric contraction;Paste extrusion;Slip law;Compressibility;Structural parameter;Flow type parameter