The effect of non-Newtonian behavior on contact formation in an external gear pump

In an extrusion process, an external gear pump can be used to control the flow rate of the system. When extruding polymers, the viscosity is quite high, resulting in negligible inertia and thus laminar flow. The external gear pump contains two gears, one driven by a motor and one driven by means of contact with the other gear. In our previous work, the flow of a viscous fluid through an external gear pump was studied using the finite element method. Local mesh refinement was applied based on the respective distance between boundaries. Furthermore, the rotation of both gears was imposed. In this work, the rotation of one gear is imposed, whereas the other gear is freely rotating. However, the minimum distance between the gears is limited to a minimum value. When this value is reached, contact is assumed and also the rotation of second gear is imposed. A reversion of the torque on this gear results in a release of contact. In this manner, a quasi driver/driven situation is created in the numerical simulations. It is observed that contact is released periodically, and thus cannot be assumed present continuously, as is often prescribed. Non-Newtonian material properties, such as shear thinning and the pressure dependence of the density or the viscosity, alter how long contact is released during a tooth rotation.