Bed Collapse, De-Aeration Rate

The rate of de-aeration of powder under different conditions is an important property in powder handling and processing. The rate of collapse of the powder in a fluidized bed is one way of measuring the rate of de-aeration but it is specific to the operating conditions the rate depends on, for example, whether or not the plenum chamber (space under the distributor) is vented simultaneously with the stopping of the aeration gas flow. 

Since relatively high velocities are to be used, the lower resistance distributor is needed for the test. 

A typical collapse curve for a group A powder is shown in Fig. 

Cohesive powders in group C display a different collapse rate as shown in Fig. 39. The bed does not bubble even at a gas velocity 

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