Simulation using Computational Fluid Dynamics (CFD, FLUENT 6.0.20) and experiments were conducted on a scaled-down cold flow model of a gas-solid fluidized bed reactor used for the production of polyethylene. Using a Eulerian-Eulerian multiphase model based on the two-phase model of Anderson and Jackson (Ind. Eng. Chem. Fundam. 1967, 6, 527-538) and Jackson (Chem. Eng. Sci. 1997, 52, 2457-2469; The Dynamics of Fluidized Bed Particles; Cambridge University Press: New York, 2000) simulations were conducted to determine the effect of several parameters; time step, differencing scheme, frictional stress, and closing equations on the bubble properties (predominantly bubble diameter). Once the model flexibility was accessed, the next step was to compare these result with those from experiments conducted using X-ray fluoroscopy. X-ray fluoroscopy was used to create a statistically significant data set. Preliminary experiments comparing the bubble diameter and axial bubble velocity were conducted using glass beads. The results demonstrated that, for glass beads, the average bubble diameters were comparable for CFD and experiments.