Author(s)

Y Jaluria

Abstract

Numerical modeling of transport in very viscous flows in complex domains, with large variations in material properties, is of particular relevance to the thermal processing of materials such as polymers, ceramics, glass, and composite materials. The basic approach to simulate these flows involves simplifying the domain and approximating the non linear coupling of the governing equations due to property variation. The main complexities that arise and the methods to treat the mare considered in this paper.Two important materials processing applications are chosen as examples to illustrate the methodology and the physical nature of the problems. These are the manufacture of optical fibers and polymer extrusion. A numerical study of the optical fiber drawing and coating processes, for relatively large draw speeds, is discussed. Large property changes occur with temperature and the geometry is complicated due to large diameter changes. A coordinate transformation is used to simplify the computational domain. The free surface, which defines the neck-down profile, is determined by using a balance of forces. The transport in the glass is calculated to obtain the temperature, velocity and defect distributions. Similarly, properties of typical polymers are strong functions of the temperature and of the shear rate, since most polymers are non-Newtonian, and the extrusion domain has to be simplified to model the transport processes. Some of the simplifications employed for the rotating environment of a single or twin-screw extruder are discussed.

Keywords