COMPUTATIONAL STUDY OF TRANSPORT PROCESSES IN A SINGLE-SCREW EXTRUDERFOR NON-NEWTONIAN CHEMICALLY REACTIVE MATERIALS

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 carrie d out to solve the governing set of partial differential equations for the velocity, temperature and species concentration fields, over a wi de range of governing parameters for the case of a tapered screw chann el. The numerical treatment for this combined heat and mass transfer p roblem is outlined. A marching procedure in the down-channel direction is adopted and the validity of the scheme for practical problems disc ussed. For large viscous dissipation, the material heats up considerab ly due to the prevailing shear field, affecting the viscosity signific antly, 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 d imensionless throughput, q(nu), is one of the most important parameter s in the numerical solution. The dimensionless pressure variation is v ery sensitive to q(nu), and orders of magnitude changes are possible f or small variations in q(nu). 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.