Numerical flow simulation for Bingham plastics in a single-screw extruder
The paper contains numerical results for an incompressible Bingham plastic flow in a single-screw extruder under isothermal and fully developed flow conditions. Results are valid only for sufficiently low Reynolds numbers. The singularity of the constitutive relation for Bingham plastics has been circumvented by approximating this relation by a sequence of smooth equations for a family of generalized Newtonian liquids. The validation of the regularization procedure has been made for a related flow problem where an analytical solution is available. A mixed finite element method has been used to transform the governing equations to a set of nonlinear algebraic equations. These have been solved by Newton method to examine the dependence of volumetric flow rate and axial pressure drop on the screw speed and on the rheological parameters. Computations predict the size and the location of the regions in the extruder channel where the Bingham material behaves like a solid and does not take part in the axial transport. The calculations also reveal that at a large Bingham number the channel depth should be relatively small, otherwise an inactive zone near the screw shall be formed where the present Bingham material does not take part in the transport process. The results of the paper would, therefore, be useful for the design of extrusion processes that prevent inactive zones of the Bingham material.
scientific article; zbMATH DE number 1080977