Quantifying Fluidizing Characteristics of Powders

The three-digit designation affords a convenient descriptive classification of powders in terms of their bed collapsing behavior, but some additional criterion is desirable to show the entire spectrum of continuous transition of fluidized states from particulate to aggregative. 

Examination of the multitude of bed collapsing curves obtained experimentally led to the recognition of the significance of a number of variables, viz., the difference between the height of the dense phase and the bed height at the critical point (Ze — Zc), which defines the extent of particulate contraction after bubbles have escaped the rate of hindered sedimentation u2 and certain physical properties of the solids and the fluid involved. These factors are organized into a dimensionless number 

If the particles are small, and their terminal velocity can be expressed by Stokes Law, u, = dp(ps — pf)g/p, then the dimensionless number is simplified to 

This dimensionless number, designated as the dimensionless subsidence time of a powder, portrays its dynamic behavior in relation to the overall bed collapsing process, inclusive of the significant variables Zx and tc. 

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