Target collection efficiency

The target collection efficiency depends on a dimensionless number, called the separation number (NJ. This separation number further depends on the separation mechanism, and the following methods are used to calculate this number. 

Dp = droplet diameter, m V = superficial gas velocity, m/sec Pg = gas viscosity, cP Dj, = target diameter, m 

For smaller particles, the momentum is not sufficient to break through the gas streamlines instead, they are carried aroxmd the object by the gas stream. In such cases, the separation number is expressed as 

Process engineering and design using Visual Basic N, = DJiWD,) (3.19) 

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P, target collection efficiency by inertial impact dimensionless... 

FIG. 14-120 Collection efficiency of wire-mesli separator 6-in thickness, 98.6 percent free space, 0.006-in-diameter wire used for experiment points. Curves calculated for target area equal to 2 and 3 times the solids volume of packing. To convert inches to millimeters, multiply hy 25.4. 

Determining the collection efficiency of the filter T from the target efficiency of the individual fibers... 

The collection efficiency of the filter may be calculated from the fiber target efficiency and other physical characteristics of the filter (Chen, op. cit.) ... 

The physical state of a pollutant is obviously important a particulate collector cannot remove vapor. Pollutant concentration and carrier gas quantity are necessary to estimate collector size and required efficiency and knowledge of a pollutant s chemistry may suggest alternative approaches to treatment. Emission standards may set collection efficiency, but specific regulations do not exist for many trace emissions. In such cases emission targets must be set by dose—exposure time relationships obtained from effects on vegetation, animals, and humans. With such information, a list of possible treatment methods can be made (see Table 1). 

This collection mode entails the use of an appropriate solid, either in the line or at the restrictor outlet, whether packed in a column or as a bed. The material used for this purpose should ensure proper retention with minimal or no analyte losses, and enable the use of the best possible type and volume of eluent to desorb the target analytes. When the extracted analytes differ in polarity, a mixture of sorbents must be used to ensure adequate collection efficiency. 

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