Biomedical Engineering Reference
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Fig. 9.2 Highly idealized model of aerosol transport from OIP through the CI system showing
potential mechanisms that could infl uence the measured APSD
Note that the presence of an induction port and in some cases also a pre-separator
is not identifi ed here. These components would also contribute to losses of particles,
primarily as the result of turbulent inertial deposition downstream of the 90° bend
of the USP/Ph. Eur. confi guration [ 4 ], and where the air fl ow direction changes take
place in the highly turbulent environment associated with fl ow through a pre-
separator [ 5 ].
The situations that Mitchell et al . considered might lead to potential EDA failure
[ 3 ] are described in the following three subsections.
9.3.1
Change of Shape in the Large Particle Mass Fraction
Alone But the Same Absolute LPM Before and Afterwards
In this fi rst situation, illustrated in Fig. 9.3 , the transfer of mass within the APSD
takes place exclusively within the size limits defi ned for the LPF . If the underlying
physical processes infl uencing the OIP aerosol are considered, both the mechanisms
of particle-particle agglomeration (coagulation) and de-agglomeration in the aero-
sol phase, as well as inertial/turbulent deposition to nearby surfaces, can account for
movements in mass from one size to another. However, considering the APSD as a
whole, Mitchell et al. [ 3 ] considered that their effects are likely never to be so selec-
tive to the extent that the small particle fraction is entirely unaffected, while just the
large particle fraction experiences the size-related shift. Instead, typically peak
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