Aerodynamic diameters of particles

When the size of a particle approaches the same order of magnitude as the mean free path of the gas molecules, the setthng velocity is greater than predicted by Stokes law because of molecular shp. The slip-flow correc tion is appreciable for particles smaller than 1 [Lm and is allowed for by the Cunningham correc tion for Stokes law (Lapple, op. cit. Licht, op. cit.). The Cunningham correction is apphed in calculations of the aerodynamic diameters of particles that are in the appropriate size range. 

For determination of the aerodynamic diameters of particles, the most commonly apphcable methods for particle-size analysis are those based on inertia aerosol centrifuges, cyclones, and inertial impactors (Lundgren et al.. Aerosol Measurement, University of Florida, Gainesville, 1979 and Liu, Fine Paiiicles—Aerosol Generation, Measurement, Sampling, and Analysis, Academic, New York, 1976). Impactors are the most commonly used. Nevertheless, impactor measurements are subject to numerous errors [Rao and Whitby, Am. Ind. Hyg. A.s.soc.]., 38, 174 (1977) Marple and WiUeke, "Inertial Impactors, in Lundgren et al.. Aerosol Measurement and Fuchs, "Aerosol Impactors, in Shaw, Fundamentals of Aerosol Sci-... 

Inertial impaction is the method of choice for evaluating particle or droplet size delivery from pharmaceutical aerosol systems. This method lends itself readily to theoretical analysis, ft has been evaluated in general terms [39] and for specific impactors [40]. Inertial impaction employs Stokes law to determine aerodynamic diameter of particles being evaluated. This has the advantage of incorporating shape and density effects into a single term. 

For determination of the aerodynamic diameters of particles, the most commonly applicable methods for particle-size analysis are those... 

The Malvern API Aerosizer (Malvern Instruments Ltd., Southborough, MA) operates on the principle of supersonic flow in a jet, followed by laser Doppler velocimetry to measure the aerodynamic diameter of particles in the size range from 0.5 to 200 pm using 50 channels. The operating flowrate is 6 L/min. The Atcor Net-2000 is a similar device for determining aerodynamic diameter, except that it is capable of sizing particles up to only 5.0 pm in diameter at a flowrate of 0.1 ft3/min (2.83 L/min). 

Runs 1, 2 and 3 (Table II) were replicate base cases with measured average aerodynamic diameters of particles of 1.52, 1.45 and 1.64 pm, respectively. A mean diameter of 1.54 pm was calculated from the three runs. Runs 4, 1, 5, 6 and 7 show that decreasing solute concentrations (from 10% to 0.1 %) reduced particle size (from 1.74 to 0.99 pm). This is consistent with the trend observed for the mannitol (see triangles and diamonds in Figure 6). The CO2 pressure effect was investigated by compressing dense CO2 from 83 to 124 and then to 207 bar. Runs 1, 9 and 8 show that average particle size decreased from 1.52 to 1.27 pm as the pressure was increased to 207 bar. The effect of dense CO2 flow... 

Figure 3 Aerodynamic diameters of particles from CAN-BD of a 0.2 % mannitol aqueous solution (Run 6 from Table 1).

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