This research seeks to develop fundamental knowledge about cohesive particle segregation that will lead to an understanding of the key flow and particle parameters that influence segregation as well as insights into how to predict and control the segregation of cohesive particles. We are using computer simulations, validated by experiments, to develop a physical understanding of the flow and segregation of cohesive particles at the flow level. This IFPRI project leverages US National Science Foundation funds for a similar project. We consider cohesive particle segregation from three viewpoints:
1) Single fine particle interactions: When a small cohesive particle collides with a large one, four scenarios can occur: bouncing-detachment, sticking-attachment, sticking-rolling-attachment, and sticking-rolling-detachment. The specific scenario that occurs depends on the combination of Bond number (Bo), restitution (e), sliding friction (μ), rolling friction (μr) and collision velocity.
2) Percolation of fines: The percolation of fine particles through a static bed of large particles (no shear) demonstrates how different combinations of Bo, e, μ, and μr can result in similar levels of fine particle trapping, indicating an underlying simplicity of cohesive particle segregation.
3) Bounded heap flow: The global effects of particle cohesive properties and shear on segregation are easily measured in terms of the segregation flux in one-sided bounded heap flow. Increasing Bo for all particles decreases segregation, as expected, although cohesion with Bo ≤ 5 has little effect on segregation due to shear. When only small particles are cohesive, increasing cohesion decreases segregation due to small particle clumping which reduces the effective size ratio; when only large particles are cohesive, increasing cohesion increases segregation due to large particle clumping, which increases the effective size ratio. Importantly, the degree of segregation is insensitive to the details of the cohesion model, making computational studies generalizable.
In year two of our effort, simulation studies will continue for the percolation of fines, to understand the influence of cohesion on segregation with and without shear, and for bounded heap flow, to explore the impact of shear on cohesive particle segregation. In addition, we are exploring wax- and polyborosiloxane-coated glass particles as well as partially-wetted particles and hydrogel particles in bounded heap flow experiments to validate simulation results.