Flow simulation with a non-Newtonian fluid

Our customer, a development engineer in a supplier company, had the task of optimizing part of a plastic extruder. It was important to him to achieve a consistent mixture of the components and a homogeneous distribution of temperature over a short distance.

Since COMSOL Multiphysics is very well suited to this task, the model was implemented using this program. An important property of plastic flows is that they do not obey Newtonian laws, i.e. the viscosity depends on the flow speed. Here in this example, the classical Carreau model has been implemented.

One of the biggest challenges was to find good estimate values for the parameters. Whereas for a large project this would typically require comprehensive measurements, the budget for this pragmatically-oriented project did not stretch this far.

Our solution was to define a physically plausible range for all areas. This resulted in a large but finite number of calculations.

We could automatically calculate this in COMSOL;  resulting in a physically plausible solution range for the target variables.

We could use this to prove that, despite the large degree of uncertainty in individual parameters, the practically-relevant target values lay within a relatively narrow window. This enabled our customer to finished designing his component with confidence, providing Production with a functioning part, on time.