Hydrodynamics plays a major role in wet grinding processes used to produce nanoparticles, but its influence on the mechanisms of fragmentation is not fully understood. The focus is on hydrodynamics in the gap between two grinding beads. Using particle image velocimetry in a large-scale experiment, the velocity field between the beads has been investigated when the beads get closer (down to one-tenth of their radius). Different configurations have been studied, varying from frontal approach to tangential collision. Finally, a capture probability of suspended particles has been estimated.