Fine Particles Spouted Bed Fluid Dynamics Characteristics Of The Numerical Analysis

The investigation of fine particle gas-spouting phenomenon has not yet been experimentally studied until now. It is hence the propose of present contribution to obtain hydrodynamics behavior of fine particle spouting in a cylindrical-conical spouted bed in connection with Eularian-Eularian two fluid modeling approach. The interaction between phases is described with the drag force, while the solid pressure and viscosity related terms in the momentum conservation equation for solid phase is closed by the well-known kinetic theory of granular flow. For such dense gas-solid flow in the spouted bed, the frictional stress is considered as well. Based on the above mentioned mathematical models set up, the influences of the parameters relating to model closure, the grid scale and time step on the simulation results have been discussed, as well as effects of the parameters relating to spouted bed structure on fine particle spouting behavior through the numerical simulation method. The numerical results about fine particle spouting hydrodynamics, such as flow regime transition, concentration field, velocity field, pressure field, et al, were compared with both experimental and simulative results reported in literatures.It is found that the Schiller & Naumann drag model results in more stable flow region for fine particle spouting than that of Wen & Yu model, Gidaspow model and Syamlal-O'Brien model, which probably results from the geometry of the spouted bed. The numerical analysis of particle velocity and voidage shows that the introduction of the Jackson& Jackson or Schaeffer frictional stress into CFD simulation results in the increase of particle velocity and voidage in the spout, which means the hydrodynamics of fine particles gas-spouting can be significantly influenced by the frictional stress, however the influence can only be observed in annulus for coarse particles. The influences of the particles restitution coefficient and the maximum packing limit on fine particle spouting are both significant, being identical with the case of coarse particle spouting. Pretest of the restitution coefficient and the maximum packing limit must be therefore conducted when no experimental datum are available.The results reveal that the geometry of the spouted bed plays a profound role on fine particle spouting. To obtain stable spouting, the optimal coupling of particle size, orifice diameter and bed diameter has to fulfill certain criteria, and the criteria for fine particle system is mostly more strictly than that for coarse particle system. However it is found that the stable spouting, for fine particle gas-spouting, is not always achievable even if the criteria were satisfied. In addition, it is recognized that fine particle is easier to achieve stable performance in a spouted bed equipped with a pipe, even if those criteria were not quite met.Conclusion could be safely drawn from the results that the grid scale and time step both influence the simulation results significantly. Mesh with the vertical grid number of three hundred is competent for traditional requirements, up to a vertical grid of four hundred eighty the simulation results is completely free from mesh size. Moreover, the time step chosen as 0.0001s is proven to be reasonable.