Riser hydrodynamics: Simulation using kinetic theory

Computational fluid dynamics (CFD) for fluidization is reaching maturity (R oco, 1998). It has become common practice to compare time-averaged solid ve locities and concentrations to measurements of fluxes and densities. The dy namic behavior of the riser, however, has not been previously compared to e xperiments. This article shows that the dynamics of solids flow in the rise r is in the form of clusters, but the time-averaged particle concentrations and fluxes give us the core-annular flow regime in agreement with measurem ents. The computed clusters, which are essentially compressible gravity wav es, produce major frequencies of density oscillations in agreement with mea surements. The model and the CFD code compute granular temperature distribu tions, agreeing qualitatively with data. For volume fraction around 3-4%, w hich is the average particle concentration in the riser, the computed visco sity agrees with our experimental measurements.