Well-designed impactors

For a well-designed impactor, a typical plot of impactor efficiency versus Vstk is shown in Fig. 7.2. It can be seen that the efficiency curve may deviate from the ideal case. In the ideal case, for all efficiencies there would be a single value of Vstk and hence a sharp size cut of the impactor. All particles larger than this size would be collected, and all smaller sizes would be passed. In actuality, this is not... 

Measurements on aerodynamic sizes of atmospheric aerosols and associated radionuclides were carried out with Anderson 2000, Inc., 1-ACFM Ambient Impactors with or without the Anderson low-pressure modification, as well as with Sierra model 236 (six-stage) high-volume impactors (HVI). The 1-ACFM design operated at 28... 

Inertial impaction is most widely applied for the characterization of inhalation systems. The principles of particle separation on the basis of inertial and drag forces have been well described for many different applications. Theoretical cut-off diameters (for particles with 50% collection efficiency) of impactors can be calculated on the basis of Stokes numbers for nozzles of a particular design [8,120]. Many different designs are available, but only a few are described in the United States and European Pharmacopoeia [121,122]. 

Impactors with various designs as well as different types of impaction surfaces are in use (e.g., see Chow, 1995). Examples include the Lundgren impactor, the Anderson sampler, the Mercer impactor, and the Uni-... 

Virtual impactors Eliminates bounce and blow off. Separated particles are left in suspension and may be transported accordingly. Sharp cut points and low losses are possible. Existing designs do not operate well at D < 2.5 fim. 

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