For the horizontal screw conveyor (Fig. 3(a)) the particles form a
heap against the leading face of the screw. After reaching the top of
the screw most of the particles tumble down the surface of the heap
and a few particles fall behind the screw shaft as pictured. There is a
slightly higher concentration of smaller (lighter grey) particles in
contact with the leading face of the screw and a higher concentration
of larger (darker grey) particles in the outer parts of the heap. This
indicates that the particles have become mildly size segregated due to
shear generated by the face of the screw. The extent of the size
segregation reported by Owen et al., [5] for a larger (125 mm) screw
conveyor rotating at 60 rpm with particle sizes ranging from 2 mm to
5 mm, was more pronounced than it is for this screw conveyor.