Development and Persistence of 'Static' or 'Dead' Zones in Flows

Abstract

Certain ceramic products are formed through extrusion processes, where a slurry is forced through small openings to form such products as filters. At the top is a large tank. The slurry is forced through the tank into an extrusion chamber, and then out through slots to form the finished product.

[The slurry may be thought of as a mixture of clay (or other polymers), water, and other binders. There are many ways to model this mixture, some of which will be discussed in this report. For instance, the slurry can be modeled as a non-Newtonian fluid, a two-phase flow with liquid and solids, or a viscoelastic fluid. One can also model the mixture as an elongated particle suspension in water, where changes in the orientation of the particles could affect the flow.]

After the extrusion process is complete, one finds that ‘dead zones’ of dry paste accumulate in two areas. Most prominently, they occur at the lower corners of the tank. They also occur on the floor of the extrusion chamber near the slots, both near and away from the walls. Since we will consider wall effects in the tank, for the extrusion chamber we consider only flow cells sufficiently far away from the walls. Then we may exploit the periodic nature of the device and consider only a single flow cell.

The aim of this project is to determine the formation mechanisms of these dead zones, and see how they affect the overall flow.