A comprehensive frictional-kinetic model for gas-particle flows: Analysis of fluidized and moving bed regimes

摘要

A comprehensive frictional-kinetic model for collisional and frictional gas-particle flows is presented. The model treats gas and particles as a continuum. The kinetic-collisional stresses are closed using kinetic theory of granular flows (KTGF). The frictional stresses are based on inertial number dependent rheology and dilation laws. From these laws the frictional normal and shear stresses are derived. These individual contributions to the solids stress tensor are treated additively, which requires a modification of the radial distribution function in the frictional regime. The presented model is validated for both, i.e. frictional and collisional dominated, flow regimes: (1) the collisional-frictional gas-particle flow in multiple-spout fluidized beds is studied and (2) the friction dominated discharge of particles from a rectangular bin is considered. In case of the multiple-spout fluidized beds the numerical simulations show excellent agreement with the experimental data of van Buijtenen et al. (2011). The numerical results demonstrate that the presented model is a substantial improvement compared to the coupled CFD-DEM simulations of van Buijtenen et al. (2011) and to the Princeton model (Srivastava and Sundaresan, 2003). In case of the discharge of particles the model predicts height-independent mass flow rates and stagnant shoulders in the corners of the bin. For the computed discharge rates excellent correlation with measurements (relative error e< 2.5%) for three different particle diameters is obtained. In contrast, the Princeton model yields relative errors up to e= 41.5%. Finally, the computed solids velocities near the exit orifice show good agreement with experimental particle tracking (PT) results as well.