Circulating Fluidized-Bed (CFB) Risers with Geldart Group B Particles Have Found Significant Application in Combustion Reactions. the Present Work Attempts to Study the Solids Flow Dynamics in a CFB Riser that is Operated with Group B Particles, using Computational Fluid Dynamics (CFD) Techniques. the Key Feature in the Present Study is that the Various Closure Schemes in the CFD Model Have Been Evaluated Against Data from Non-Invasive Experimental Techniques: Computer Automated Radioactive Particle Tracking (CARPT) for Solids Velocity Field and Computed Tomography (CT) for Solids Holdup. Since Solids Flow in a Riser is Multiscale in Character, in Addition to the Measured Averaged Solids Velocity Profiles and Solids' Fraction Profiles in the Experimental Section, Mean Granular Temperature Profiles Have Also Been Compared. Two Flow Regimes (Viz., Fast Fluidization and Dilute Phase Transport) Have Been Considered in This Study. © 2007 American Chemical Society.