Flow patterns in high-velocity fluidized beds and pneumatic conveying

Four flow patterns are identified for gas-solids vertical upward flows. Hom ogeneous dilute phase flow is characterized by the absence of both radial a nd axial solids segregation. Heterogeneous dilute phase flow (also called c ore-annulus flow) is characterized by the absence of axial solids segregati on, with solids carried upward in the core and travelling downward near the outer wall due to the formation of particle streamers. Collapsed flow with a lower dense region and an upper dilute region is also referred to as the fast fluidization regime. In this case, the flow structure in the upper di lute region is similar to that in heterogeneous dilute phase flow, while th e lower dense region resembles that in a turbulent fluidized bed. Dense pha se flow can be reached when the riser is completely occupied by a relativel y dense suspension with little axial density variation and no net solids do wnflow near the riser wall. The transition from fast fluidization to dense phase flow is still not clearly defined.