When the fluid passes through the bed at the rate of gradual improvement to a certain value, the particles become loose, the gap between the particles increases, the bed volume expansion. If the fluid speed is further improved, the bed will not be able to maintain a stationary state. At this point, the particles are suspended in the fluid, showing a fairly irregular movement. With the increase of flow velocity, the particles movement more intense, the bed swelling also increases, but the particles remain in the bed and not the fluid. This state of the bed is similar to the liquid as a fluidized bed. Among them, the type of fluidized bed is: the smallest fluidized bed, bubble fluidized bed, teng fluidized bed.