Permeability and Deaeration

Another useful classification technique that makes use of two different bench-type experiments (i.e., permeability and deaeration) has been presented by Mainwaring and Reed (1987). The above three classifications are described in the following sections. 

Permeability and Deaeration Various states of fluidization and pneumatic conveying exist for bulk solid. Fluidization and aeration behavior may be characterized by a fluidization test rig, as illustrated in Fig. 21-25. A loosely poured powder is supported by a porous or perforated distributor plate. The quahty and uniformity of this plate are critical to the design. Various methods of filling have been explored to include vibration and vacuum fiUing of related permeameters... 

FIG. 21-31 Classificatto conveying based on combined permeability and deaeration factors, based on Jones and Miller. [Sanchez etal. Powder... 

Permeability (or fluidization) and deaeration characteristics of the material (Mainwaring and Reed, 1987 Jones and Mills, 1989), which depend strongly on the above parameters... 

Also, it seems that most of these properties are interdependent. For example, deaeration and permeability (Mainwaring and Reed, 1987) and perhaps the bulk density ratio (Jones and Mills, 1989) seem to provide an adequate mechanism to detect changes in material performance due to different particle size distribution, density and/or shape. However, possibly the greatest disadvantage or limitation of these empirical techniques is the need to standardize the experimental apparatus and techniques. For exam-... 

Higher flow rates than the calculated critical flow rate may occur, but can result in non-steady or erratic feed and the resulting adverse effects. Permeability values can also be used to calculate the time required for fine powders to settle or deaerate in equipment. 

FIG. 21-30 Classification of pneumatic conveying based on [a] permeability factor and (fc) deaeration factor. [From Mainwaring and Reed, Bulk Solids Handling, 7, 415 (1987) with permission.]... 

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