Packings aerodynamics

FIG. 14-119 Aerodynamic cut diameter for a tyj)ical packed-bed entrainment separator as a function of pacldng size, bed depth, and three gas velocities curve 1-1.5 m/s, curve 2-3.0 m/s, and curve. 3-4.5 m/s. To convert meters to feet, multiply by. 3.281 to convert centimeters to inches, multiply by 0..394. [Calveti, J. Air Pollut. Control Assoc., 24, 929 (1974).]... 

Woods DA. 1986. Final product dust activity median aerodynamic diameters in the product packing areas of two Australian uranium mills. Health Phys 51 352-356. 

An aerodynamic interaction between the gas and the solids, mainly controlled by the dynamic viscosity of the gas and the elasticity of the packed solids. 

EFFECTIVE (OR AERODYNAMIC) PARTICLE DENSITY is when the measured volume includes both the closed and the open pores. This volume is within an aerodynamic envelope as seen by the gas flowing past the particle the value of density measured is therefore a weighted average of the solid and immobilised gas (or liquid) densities present within the envelope volume. The effective density is clearly of primary importance in applications involving flow round particles like in fluidization, sedimentation or flow through packed beds. 

The use of the effective (aerodynamic) particle density is largely restricted to fluidization and pneumatic conveying applications at the moment. It is, however, potentially useful in other areas like particle size measurement by sedimentation or elutriation, or flow through packed beds where it has not yet been fully accepted. 

The aerodynamic aspect of vapour flow in packed columns has been dealt with by Barth [220], who demonstrated that packing having sharp angles gives rise to two or three times the pressure drop caused by rounded bodies. 

The old filter makers methods of packing in more media with the hope that the increased area would reduce the media velocity has distinct limitations since the extra area is not effectively used by the poor aerodynamics created. Instead a careful aerodynamic design ensured a more even distribution throughout the filter. 

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