4. Turbulent fluidization, transported beds, circulating beds

If the fluidization speed is increased beyond the usual values for bubbling fluidization, at some point the bubbles lose their regular shape and form vertical jets of varying size in the fluidized bed. This turbulence in the fluidized bed is such that not only do bubble formation and coalescence become random, but it also becomes difficult to distinguish the bed surface. Under these conditions, the concepts and theories developed for bubbling fluidized beds are no longer valid, and cannot correctly describe the behavior of the bed, particularly with regard to bubble/suspension material transfer.

A great deal of research has been devoted to defining the limiting velocity of bubbling fluidization, known as the transition velocity. However, no particular theory has emerged from this work. In fact, the transition from bubbling to turbulent fluidization is gradual and...