A computational fluid dynamics model was developed for gas-solid fluidized
beds containing a mixture of two particle species. To calculate stresses of
the solid phase, the kinetic theory of granular flow was extended to consi
der a binary mixture of smooth, nearly elastic, spheres. The developed mode
l was simulated to demonstrate key features of binary mixture fluidization.
Bed expansion with a binary mixture of different size panicles, but with i
dentical densities, was much higher than that of a system consisting of mon
o-sized particles of the same mean size as the bimodal mixture. Minimum flu
idization velocity for the binary particle system was significantly lowered
. The mixing behavior- of the binary mixture of particles, characterized by
the mixing index, increased with increasing superficial gas velocity. For
a binary mixture of particles of larger size with lower density and smaller
site with higher- density larger; lighter particles segregated to the top
of the fluid bed while smaller, heavier particles segregated to the bottom.
With increasing fluidization velocity, this segregation pattern reversed a
nd "inversion occurred. The drag and gravity force difference between small
, heavy particles and large, light particles was dominant at low gas veloci
ties. With an increase in gas velocity, however the gradients in granular t
emperature and pressure became dominant terms in the equations for the rela
tive force and thus velocity between two different particle species.