Rotational behavior of dry spheres obliquely impacting on liquid layers

• The configuration of the liquid bridge is largely affected by the liquid viscosity.
• ω increases with the tangential velocity.
• ω decreases with the increasing of layer thickness and liquid viscosity.
• Ω decreases first and then increases with the increasing tangential StN.
• The computed β and μf for the wet impact are different from the dry case.

Sphere collision with the presence of liquid is common in industrial fluidization-based processes. A detailed understanding on its mechanics is helpful for optimizing these processes. There have been some studies regarding energy dissipation in terms of restitution coefficients. However, studies on rotational characteristics of spheres after impact are scarce. In this work, experiments are conducted to trace Al2O3 spheres obliquely impacting on a surface covered by liquid layers. Strong rotation can be observed when the sphere rebounds after the impact. The effects of tangential velocity, liquid viscosity and layer thickness on the angular velocity of spheres (ω) were investigated. It is found that ω decreases with increasing liquid layer thickness and viscosity, while increases with the tangential velocity. Furthermore, the quantitative relation of angular velocity to these impact parameters was analyzed by using a modified Stokes number (StN). Finally, two characteristic parameters, rotational restitution coefficient (β) and friction coefficient (μf), were calculated to distinguish rolling and sliding regions during contact.

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