Conference Dates

May 16-21, 2010


The normal impact of spherical particles (elastic glass, elastic-plastic Al2O3) and non-spherical dominantly plastic agglomerates of amorphous maltodextrin on a wall with a liquid layer was studied. The objective was to investigate the effects of thickness (0.1-1 mm) and viscosity of the liquid layer (1-250 mPas) as well as of the impact velocity (1-3.0 m/s) of the granule on the restitution coefficient. The restitution coefficient was measured by using a free-fall apparatus. In the presence of a liquid layer, the higher the viscosity and thickness of the liquid layer the more the energy dissipated during impact and the smaller the critical thickness needed for the sticking of the particle. The measured restitution coefficients were compared with experiments performed without liquid layer. In contrast to the dry restitution coefficient, due to viscous losses at lower impact velocity, higher energy dissipation was obtained. A rational explanation for the effects obtained was given by establishing and numerically solving the force and energy balances for particles impacting on a liquid layer. The model takes into account forces acting on the particle, which includes viscous forces, surface tension and capillary forces, contact forces due to deformation of the wall, drag forces, buoyancy and gravity. A good agreement between simulations and experiments has been achieved. The results are essential for estimating the adhesion probability during agglomeration processes and crusting on equipment surfaces.