Fluidization in a riser: Granular temperature and stresses

Detailed experimental velocity, particle concentration and stresses for flow of particles in a vertical pipe, riser are needed for verification of various CFD models for multiphase flow. This is the principle-unsolved task of the Fluid Dynamics Multiphase Flow Consortium, organized by Dow Chemical Company. This study provides such information for flow of 530 mum glass beads in the fully developed flow region of a 7 m symmetric riser with a splash plate. Instantaneous particle velocity distributions were obtained using a particle velocity imaging technique and a probe inserted into the riser, while the particle concentrations were measured with a gamma-ray densitometer.;Time averaged particle velocity distributions can be well represented by a parabolic velocity distribution, with the mean velocity obtained from flux divided by the measured bulk density. The radial granular temperature profiles agree with an analytical expression similar to the thermal temperature distribution in Poiseuille flow with viscous heat generation. In this approximate analysis the particles are assumed to be completely elastic. A ratio of shear stresses to normal stresses gives the restitution coefficients in the range of 0.975 to 0.999. In the core the Reynolds stresses are much smaller than the velocity averaged particle stresses, while near the wall the time averaged Reynolds stresses are large.;A numerical solution to the complete kinetic theory model shows that the flow is in the developed core-annular regime and the approximations made in the analytical solution are valid.