There are noticeable differences of local voidage
profiles for different specularity coefficients, especially near the
wall. The solid-phase wall boundary condition determines the
movement of particles along the wall, thus significantly affecting
the voidage profiles near the wall. Also, the effect of specularity
coefficient on voidage profile is significantly different at the three
cross sections. For the cross section at 4.5 m, all radial voidage profiles
are similar since their average voidages are close as shown
in Fig. 3. The particles concentrations for the lower and upper riser