Propagation velocities of pressure disturbances were detd. conveniently in a bubble-free fluidized bed by impulsive step compression of the bed free surface. The pseudo-homogeneous model provided a first approxn. approach to the evaluation of propagation velocities of pressure disturbances in bubble-free fluidized beds of solids of different properties. Close to the bed min. bubbling velocity, group A and B solids conformed to the model predictions with regard to the effect of particle d. on the propagation velocity. On the contrary, close to the bed min. fluidization velocities, considerable discrepancies were obsd. between calcd. and measured velocities. The largest discrepancies were shown by group D and B-D solids, which had min. fluidization and min. bubbling velocities almost coincident with each other. This suggested that particle size and d. affected the propagation velocity of pressure disturbances indirectly, via variations of bed voidage and of the width of the voidage interval between min. fluidization and min. bubbling velocity.
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