NONISOTHERMAL MODEL OF SINGLE-SCREW EXTRUSION OF GENERALIZED NEWTONIAN FLUIDS

A nonisothermal model of the single - extrusion Processing of generali zed Newtonian fluids is presented. Various temperature dependent forms of a generalized Newtonian fluid constitutive equation representing t he Herschel-Bulkley fluid and its simplifications, including Bingham p lastic, power law of Ostwald-de Waele, and Newtonian fluids, are appli cable. The model includes the generally ignored transverse convection terms of the equation of energy. The importance of keeping the transve rse convection terms in the analysis is demonstrated by applying the m odel and comparing findings to experimental results involving the tran sverse flow temperature distributions in single screw extruders, avail able in the literature. The numerical instabilities, arising principal ly from the convection terms, generally encountered in high-Peclet-num ber extrusion flows, could be eliminated by the use of the streamline upwind / Petrov-Galerkin formulation. The model is sufficiently genera l to accommodate Navier's wall slip at the wall boundary condition com monly encountered during the processing of gels and concentrated suspe nsions.