Investigation of mixing/segregation of mixture particles in gas–solid fluidized beds

A multi-fluid computational fluid dynamics (CFD) model based on kinetic theory of granular flow and Eulerian–Eulerian approach for binary mixture of particles was presented. The multi-fluid model with gas phase and two particle phases of either different particle sizes or densities is used to simulate flows in bubbling gas–solid fluidized beds. The flow behavior of particle mixing or separation in bubbling fluidized beds was numerically predicted. Details of particle collision information were obtained through tracing particle motions based on Eulerian–Lagrangian approach coupled with the discrete hard-sphere model. The distributions of volume fraction, velocity and granular temperature of particles of two different sizes or densities were obtained. The discrete hard-sphere modeling results quantified the granular temperatures, particle fluctuating velocities, particle phase stresses, as well as the particle shear viscosities. The simulations using both the multi-fluid model and the discrete hard-sphere model clearly indicate particle separation phenomenon in the fluidized beds, where relatively larger or heavier particles are observed near the bed bottom than at the bed top region while relatively smaller or lighter particles were found at bed top than at the bed bottom. Better particle mixing can be obtained by increasing the fluidizing velocity.