Influence of the surface roughness on the collision behavior of fine particles in ambient fluids

Particle-wall collisions appear in many different processes of particle technology. During a collision, different micro processes, such as friction, plastic deformation and adhesion can take place in the contact and lead to an energy dissipation. The surrounding fluid between particle and wall can also decrease the impact velocity due to viscous forces. This study focuses on the influence of the surface roughness on particle-wall collisions in ambient air and water. The single particle impact tests were performed with spherical zirconium oxide particles on a polished and an untreated titanium surfaces to investigate the energy dissipation during collision in a wide range of Stokes numbers (20–8900) depending on the surface roughness. A 3D high-speed camera system was used to obtain the particle impact and rebound behavior. The particle and wall roughness were measured with confocal microscopy and scanning probe microscopy, from which an equivalent roughness parameter was derived. The experiments showed that with an increase of the roughness, the coefficient of restitution decreases in air, while increasing during collisions in water. An elastohydrodynamic model of particle collision on the wall covered by a liquid layer was used to predict the coefficient of restitution for the contact in ambient fluids while considering measured roughness parameters.