Computational fluid dynamics of circulating fluidized bed downer: Study of modeling parameters and system hydrodynamic characteristics

In this study, the effects of various modeling parameters were explored and summarized in the circulating fluidized bed downer. They are specularity coefficient, restitution coefficient between solid particle and wall, restitution coefficient between solid particles, interphase exchange or drag coefficient model, inlet granular temperature and inlet configuration.The downer of circulating fluidized bed was then successfully simulated using computational fluid dynamics model with the Eulerian approach, the kinetic theory of granular flow and the best fitted modeling parameters. The computations gave a close comparison of the solid volume fraction, solid mass flux and system gauge pressure with three different experimental conditions. Finally, the obtained computational fluid dynamics model was applied to calculate the system hydrodynamic characteristics and the system turbulent properties, which are the solid volume fraction, the axial solid velocity, the radial solid velocity, the power spectrum, the normal Reynolds stresses, the turbulent kinetic energy, the granular temperature and the energy spectrum. These calculated results can be used as an explanation for the in-depth system flow structure in the downer system.

► Effects of modeling parameters were summarized in circulating fluidized bed downer.
► Drag, inlet granular temperature and inlet arrangement have large effect on downer.
► Downer was successfully simulated using computational fluid dynamics (CFD) model.
► Model was applied to compute hydrodynamic characteristics and turbulent properties.
► Result can be used as explanation for the in-depth system flow structure in downer.