NUMERICAL ISSUES ON THE CFD PREDICTION OF BIDISPERSE GAS-SOLID FLUIDIZED BEDS

The aim of this work is to investigate a bidisperse gas-solid fluidized bed by a Computational Fluid Dynamics (CFD) approach based on the multi-fluid model and to identify the influence of numerical issues on the accuracy of the bed segregation predictions. The selected simulation approach is based on Eulerian unsteady equations of motion for each phase coupled with the granular kinetic theory. The effect of grid size and time step on axial segregation of two different binary solid mixtures is investigated. The analysis of the simulation results, which implement previous findings with new data, confirms that firm conclusions on the capacity of the CFD model to predict the segregation dynamics in fluidized beds can be drawn only after careful verification of numerical uncertainties at the operating conditions under investigation. The results clearly show that an important contribution to the mismatch of computed and experimental axial segregation is due to numerical errors, which in turn strongly depend on the particular operating condition under consideration. The relationship between the average absolute error and a global parameter, which takes into account both the operating conditions and the spatial and temporal resolutions, is shown.