Rheological investigations on free-flowing and cohesive powders in different states of Aeration, using a ball measuring system

For many industrial applications, knowing the bulk properties of powders is a crucial factor. Even though, the simulation of idealized, particulate systems has become state of the art, a comprehensive description of industrially utilized powders is still challenging, if not impossible. Conducting measurements is imperative to gain knowledge about the flow behavior of a powder, either for direct application in engineering, or for the validation of simulations.

We investigate an alternative method for measuring the apparent viscosity of granular materials, meeting challenges associated with free-flowing and cohesive powders. The method is based on the measurement of a typical drag force, acting on a sphere when dragged through a powder bed. From the measured torque signal, the apparent viscosity is calculated via Stokes drag law. To connect the measured viscosity with a typical flow metric, a theory providing an averaged shear rate has been developed. Results obtained with the newly developed sphere-based measuring system are compared to data from other well investigated flow setups.

Our results suggest that our method is capable of measuring the apparent viscosity of free-flowing and cohesive powders. Furthermore, we demonstrate that the derived shear rate theory suitably approximates the complex flow field in the measuring setup for a range of applications.