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back of the filter screen except during the sampling periods,
2.2.3 Discussion of Possible Errors in Sampling.
Polydisperse aerosols
contain an aggregate of particles whose sizes are arranged in accordance with
a characteristic frequency distribution,
When the aerosol is sampled under |
ideal conditions, the ratios of the numbers of particles in the varjous size
ranges will be preserved unchanged in the collectors
However, a departure
from the initial size distribution: may be encountered if the collecting device
has'a dimensional bias (non-isokinetic condition), or if some of the particles
are broken up during the sampling operation.
Isokinetic sampling conditions will be achieved with a filtering device
moving through the aerosol at subsonic speeds if the air velocity into the
intake of the filter is identical with the flow rate past the outside,
As used
in Project 2.8, both the wing tank and coincident samplers were close to
isokinetic since the velocity ratios were respectively 0.8 (or greater) and
-
0.7-0.9.
calculated
However, in a few cases, the/velocity ratios for the coincident
units were much less,due to malfunction of the sanupling equipnent - (see
Appendix B),
The E-1 sampler used on the WB-50's was'poor isokinctically,
but this was considered to be immaterial for height line sampling where the
particles in a given region should be fairly uniform in size,
Samplers, such
as the project rockets, which move at supersonic speed with respectto the
aerosol are expected from aerodynamic theory to be unbiased,
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