Riser hydrodynamics: Simulation using kinetic theory

Computational fluid dynamics (CFD) for fluidization is reaching maturity (Roco, 1998). It has become common practice to compare time-averaged solid velocities and concentrations to measurements of fluxes and densities. The dynamic behavior of the riser, however, has not been previously compared to experiments. This article shows that the dynamics of solids flow in the riser is in the form of clusters, but the time-averaged particle concentrations and fluxes give us the core-annular flow regime in agreement with measurements. The computed clusters, which are essentially compressible gravity waves, produce major frequencies of density oscillations in agreement with measurements. The model and the CFD code compute granular temperature distributions, agreeing qualitatively with data. For volume fraction around 3–4%, which is the average particle concentration in the riser, the computed viscosity agrees with our experimental measurements.