Computational study of transport processes in a single-screw extruder for non-newtonian chemically reactive materials

Abstract

A numerical study of the transport phenomena arising in a single-screw extruder channel is carried out. A non-Newtonian fluid is considered, using a power law model for the variable viscosity. Chemical reaction kinetics are also included. Finite difference computations are carried out to solve the governing set of partial differential equations for the velocity, temperature and species concentration fields, over a wide range of governing parameters for the case of a tapered screw channel. The numerical treatment for this combined heat and mass transfer problem is outlined. A marching procedure in the down-channel direction is adopted and the validity of the scheme for practical problems discussed. For large viscous dissipation, the material heats up considerably due to the prevailing shear field, affecting the viscosity significantly, and results in large changes in the pressure development at the end of the channel. The rate of reaction controls the mass diffusion rate which in turn affects viscosity and the flow significantly. The dimensionless throughput,q v , is one of the most important parameters in the numerical solution. The dimensionless pressure variation is very sensitive toq v , and orders of magnitude changes are possible for small variations inq v . Schemes for dealing with other important effects such as back flow, heat transfer by conduction in the barrel, and the effect of the die are also outlined.