A numerical study of fluidization characteristics in transition from aggregative to particulate flow

A comparative study on the fluidization characteristics from aggregative to particulate fluidization with increasing fluid density and viscosity is carried out using the two-fluid models (TFM), to study the vast transitional states in between. Two representative transitional fluidization states are observed as the fluidized state changes progressively from aggregative to particulate fluidization. As the discrimination number (D_n) adopted to delineate the transition decreases, the increasing number of local vortexes promotes more internal particle circulation, and a reduction in the bubble phase and the dense phase fractions but an increase in solids holdup in the intermediate phase. As a result, the intermediate phase become more interconnected and solids movement are enhanced. The interaction between the solids and the fluid phases is also increased and the intensity of particle-particle interaction is decreased with decreasing D_n. Fluid density has more significant effect on the above changes than fluid viscosity.