Linking particle properties to dense suspension extrusion flow characteristics using discrete element simulations

The role of inter-particle friction on rheology and texture of wet granular flows

In order to get insight into the rheology and texture of rough unsaturated granular flows, we study the effects of the inter-particle friction coefficient on the macroscopic attributes and the texture variables of steady-state shearing flow of wet granular materials by relying on three-dimensional (3D) particle dynamics simulations. The macroscopic attributes are characterized by the macroscopic friction coefficient, macroscopic cohesion, and the packing fraction. The microstructural variables are characterized by the fabric and force anisotropies, the coordination number, and the stress transmission ratio. We show that the macroscopic observables behave as a function of the inertial number as a dry case for different values of the inter-particle friction coefficient. In particular, the macroscopic friction coefficient increases and the packing fraction decreases rapidly for small values of the friction coefficient, then they almost reach plateaus for higher values of the friction coefficient. Interestingly, all the macroscopic observables nicely behave as a function of the small values of the friction coefficient. Similarly, we also observe these characteristics for the fabric and force anisotropies and the coordination number as well as the stress transmission ratio which reflects the intermediate relationship between the microstructure and the mechanical behavior of such flows.

Viscosity Estimation of a Suspension with Rigid Spheres in Circular Microchannels Using Particle Tracking Velocimetry

Suspension flows are ubiquitous in industry and nature. Therefore, it is important to understand the rheological properties of a suspension. The key to understanding the mechanism of suspension rheology is considering changes in its microstructure. It is difficult to evaluate the influence of change in the microstructure on the rheological properties affected by the macroscopic flow field for non-colloidal particles. In this study, we propose a new method to evaluate the changes in both the microstructure and rheological properties of a suspension using particle tracking velocimetry (PTV) and a power-law fluid model. Dilute suspension (0.38%) flows with fluorescent particles in a microchannel with a circular cross section were measured under low Reynolds number conditions (Re ≈ 10^-4). Furthermore, the distribution of suspended particles in the radial direction was obtained from the measured images. Based on the power-law index and dependence of relative viscosity on the shear rate, we observed that the non-Newtonian properties of the suspension showed shear-thinning. This method will be useful in revealing the relationship between microstructural changes in a suspension and its rheology.

Liquid Migration in Shear Thickening Suspensions Flowing through Constrictions

Dense suspensions often become more dilute as they move downstream through a constriction. We find that as a shear-thickening suspension is extruded through a narrow die and undergoes such liquid migration, the extrudate maintains a steady concentration ϕ_{out}^{LM}, independent of time or initial concentration. At low volumetric flow rate Q, ϕ_{out}^{LM} is a universal function of Q/r_{d}^{3}, a characteristic shear rate in the die of radius r_{d}, and coincides with the critical input concentration for the onset of LM, ϕ_{in}^{crit}. We predict this function by coupling the Wyart-Cates model for shear thickening and the "suspension balance model" for solvent permeation through particles.