Experimental study of oblique impact between dry spheres and liquid layers

Liquid addition is common in industrial fluidization-based processes. A detailed understanding of collision mechanics of particles with liquid layers is helpful to optimize these processes. The normal impact with liquid has been studied extensively; however, the studies on oblique impact with liquid are scarce. In this work, experiments are conducted to trace Al_{2}O_{3} spheres obliquely impacting on a surface covered by liquid layers, in which the free-fall spheres are disturbed initially by a horizontal gas flow. The oblique impact exhibits different rebound behaviors from normal collision due to the occurrence of strong rotation. The normal and tangential restitution coefficients (e_{n} and e_{t}) and liquid bridge rupture time (t_{rup}) are analyzed. With increase in liquid layer thickness and viscosity, e_{n} and e_{t} decline, and t_{rup} increases. With increase in tangential velocity, e_{t} decreases first and then increases, whereas e_{n} remains nearly unchanged, and t_{rup} decreases constantly. A modified Stokes number is proposed to further explore the relation between restitution coefficients and the impact parameters. Finally, an analysis of energy dissipation shows that the contact deformation and liquid phase are the two main sources of total energy dissipation. Unexpectedly, the dissipative energy caused by the liquid phase is independent of tangential velocity.