ENTRY AND EXIT FLOWS OF BINGHAM FLUIDS

Entry and exit flows through extrusion dies are studied numerically for Bingham fluids exhibiting a yield stress. A constitutive equation proposed by Papanastasiou is used, which applies everywhere in the flow field in both yielded and practically unyielded regions. The emphasis is on determining the extent and shape of unyielded/yielded regions along with the extrudate swell (contraction) for planar and axisymmetric dies. The results for pressure are used to determine the excess pressure losses that give rise to entrance, exit, and the total end (or Bagley) correction.