Flow Inside the Extruder

More complicated models have been published in the open literature [47], while the first fidly 3D computational effort of the whole extmder was made in 1984 [48] based on the assumption of a very viscous fluid even for the soUds-convqring zone. Since then, more computational effort has been expended on the subject. For example, the work of Moysey and Thompson [49] uses the discrete element method to study interactions of polymer pellets as they flow in the solids-conveying zone. These authors have shown interesting patterns in the extmder, which can be used for analysis and design, albeit on a much more demanding basis due to the fidl 3D nature of the geometry. 

In all these cases of simulation inside extruders, the major focus has been the development of efficient geometry modules to describe in a quick and user-friendly way the complicated geometrical characteristics of screws and extruder charmels. The question of adequately describing the rheology of the polymer melt is usually resolved with good viscosity data as a function of shear rate and temperature (Eq. (4.19)). The Carreau model (Eq. (4.6)) for the former and the exponential model (Eq. (4.9)) or Arrhenius model (Eq. (4.10)) for thelatter are sufficientin these computations, where viscoelasticity does not seem to be of importance or has not been attempted in any meaningful way. The predominance of shear flow inside the extruder seems to be the justification for that. 

---

The heat transfer and flow inside the extruder are calculated by solving the classical continuum mechanics equations (mass, momentum and energy balances), according to the local geometry and boundary conditions. 

---