Biomedical Engineering Reference
In-Depth Information
Table 8.8
A comparison of particle deposition efficiency for Asbestos, the MMVF and other
arbitrary fibres with varying
ρA
cross
values
Density
Diameter
ρA
cross
Length
d
ae
Equivalent d
ae
(kg/m
3
)
(
μ
m)
(kg/m)
(
μ
m)
(
μ
m)
total deposition (%)
Asbestos
300
1
300
10
1.09
0.00
100
1.44
0.01
300
1.59
0.02
10
7.60
10.1
MMVF
1,830
3.66
19,390
100
11.38
42.8
300
12.84
60.1
10
5.49
2.8
Fibre 1
1,000
3.56
10,000
100
8.20
13.5
300
9.25
21.2
10
10.69
35.1
Fibre
2
3,190
4
40,000
100
16.18
90.7
300
18.31
98.1
most significant in the smaller length range. The
ρA
cross
value for asbestos and the
MMVF fibre is 300 and 19,390, respectively.
For asbestos fibres at the same length range, the
d
ae
range is 1.0-1.6
m. This is
due to the properties of asbestos that exhibit a light density and small cross-sectional
diameter and cause the
d
ae
to be independent of its length.
μ
8.3.3.4
Deposition Patterns of Submicron and Nanoparticles
The diffusion deposition of submicron particles (1-150 nm) was simulated under
flow rates of 4, 10 and 15 L/min (Wang et al. 2009). Comparisons of the simu-
lated results were made with the available experimental data reported by Cheng
et al. (1996) which investigated a variety of nasal cavities with different anatomical
features. Here the solid lines correspond to the model prediction. High deposition
reaching 80 % was found for 1 nm particles (Fig.
8.31
). High diffusion deposition is
found for particles up to approximately 50 nm where particles that are larger provide
little change in the total deposition. The deposition for 50 nm or larger particles is
approximately 10 %. As discussed earlier, differences in the results may be attributed
to anatomical variances in the nasal cavities used. In summary, the good agreement
between published experimental data and simulated results instill confidence that
the present simulation model is sufficiently accurate to analyse laminar fluid flow as
well as particle deposition in the three-dimensional nasal cavity.
You may have noticed from the previous section that micron particles deposit by
inertial impaction caused by the particle's inertia. For submicron particles, there is an
inherent difference in the deposition mechanism. The motion of a submicron particle
is governed by Brownian diffusion, which then leads to diffusion deposition. If one
is to think of the diffusion of a teabag in hot water, the motion of submicron particles
dispersing randomly is similar. Thus the deposition patterns for a submicron particle
and a micron particle are compared here to highlight their differences.
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