On the effect of cluster resolution in riser flows on momentum and reaction kinetic interaction

Fine grid simulations of reactive gas–solid flows in a riser were carried out using an Eulerian multi-fluid kinetic theory of granular flow (KTGF) approach. A translationally periodic section of the riser was used to replicate experimental data collected in the fully developed region of a tall riser. The spatial and temporal resolution was varied in designed experiments to find an appropriate compromise between overall numerical accuracy and computational time. Results revealed that, when first order implicit timestepping is used, no timestep independence could be reached with timestep sizes that are practically feasible. Timestep independence could only be achieved by using second order implicit timestepping. Grid independence was studied in terms of cell width and cell aspect ratio. Solution independence could be reached at a cell width in the range of 10 particle diameters, but no complete grid aspect ratio independence could be achieved. Results suggested that grids with an aspect ratio smaller than one might be necessary to attain grid independent solutions. When sufficiently fine grids are used, however, the effect of a change in aspect ratio is sufficiently small to attain accurate solutions with an aspect ratio of two or lower. Certain important conversion measures were identified for scaling between simulation results collected in a 3D cylindrical domain and those predicted by a 2D planar simulation. System behavior predicted using these scaling rules agreed well with experimental results.