Modeling and Simulation of a Biopolymer Processing in a Single Screw Extruder - Selected Topics of Computational and Experimental Fluid Mechanics - page 445

Fig. 3 Velocity profile
created by combining drag
flows and pressure flows with
a positive pressure gradient
Fig. 4 Velocity profile
generated by the
combination of drag and
pressure flows with positive
pressure gradient for
different values of power law
index “n”
with slope equal to the viscosity is obtained, as expected. In Fig. 3 the combination
of the drag flow and the pressure flow generated by a positive gradient pressure for
a Newtonian fluid is shown.
Figure 4 shows the effect of the power law index “n” in the velocity profile gen-
erated by the combination of drag and pressure flows, as expected for shear thinning
fluid with reducing “n” the viscosity decreases, thus having a lower resistance to
flow modifying the velocity profile.
The temperature profile for different screw speeds is shown in Fig. 5 . The model
considers the viscous dissipation term. This implies that increasing the velocity there
also increases the fluid temperature as shown in this figure. This is very important
when setting the operating conditions because at high screw speeds the screw can be
degraded thermally and mechanically affecting the final product.