Abstract
Eulerian two fluid approach is generally used to simulate gassolid flows in industrial circulating fluidized beds. Because of limitation of computational resources, simulations of large vessels are usually performed by using too coarse grid. Coarse grid simulations can not resolve fine flow scales which can play an important role in the dynamic behaviour of the beds. In particular, cancelling out the particle segregation effect of small scales leads to an inadequate modelling of the mean interfacial momentum transfer between phases and particulate shear stresses by secondary effect. Then, an appropriate modelling accounting for influences of unresolved structures has to be proposed for coarsegrid simulations. For this purpose, computational grids are refined to get meshindependent result where statistical quantities do not change with further mesh refinement for a 3D periodic circulating fluidized bed. The 3D periodic circulating fluidized is a simple academic configuration where gassolid flow conducted with Atype particles is periodically driven along the opposite direction of the gravity. The particulate momentum and agitation equations are filtered by the volume averaging and the importance of additional terms due to the averaging procedure are investigated by budget analyses using the mesh independent result. Results show that the filtered momentum equation of phases can be computed on coarse grid simulations but subgrid drift velocity due to the subgrid correlation between the local fluid velocity and the local particle volume fraction and particulate subgrid shear stresses must be taken into account. In this study, we propose functional and structural models for subgrid drift velocity, written in terms of the difference between the gas velocitysolid volume fraction correlation and the multiplication of the filtered gas velocity with the filtered solid volume fraction. Particulate subgrid shear stresses are closed by models proposed for single turbulent flows. Models’ predictabilities are investigated by a priori tests and they are validated by coarsegrid simulations of 3D periodic circulating, dense fluidized beds and experimental data of industrial scale circulating fluidized bed in manner of a posteriori tests.
Original language  English 

Qualification  Ph.D. 
Awarding Institution 

Supervisors/Advisors 

Award date  18 Oct 2011 
Publication status  Published  2011 