Feed Behavior with Shear Thinning

In all respects, the smaller pitch is the better choice. If with values that are otherwise the same, the picture is a throughput of 500 1/h is conveyed different (Example 2). 

For a pitch of 40 mm, the throughput per revolution is now much higher than at the optimum energy level, resulting in an unfavorable operating point. In this case, a pitch of 60 mm would be the better choice. This example clearly shows that no screw element is best in all situations. Rather, the choice of suitable screw element depends significantly on the dimensionless throughput. 

6 Pressure and Energy behavior with Shear Thinning 

If the material to be processed is subject to shear thinning, the linear relationships for the pressure and energy behavior illustrated above no longer apply. With shear thinning, there is a non-linear relationship between the shear rate and shear stress that is reflected in the flow curve (see Chapter 3). As a rule, the zero viscosity and one or two rheological time constants are enough to describe the flow curve with sufficient accuracy. The Carreau equation is often used it contains a dimensionless flow exponent in addition to the zero viscosity and a rheological time constant. 

The dimensionless flow exponent m and the rheological time constant are additional influencing variables that turn the one-dimensional problem for Newtonian fluids into a three-dimensional problem. The rheological time constant , when multiplied by the revolution speed n, forms an independent dimensionless group (Deborah number). 

---