Case Studies in the Human Respiratory System - Computational Fluid and Particle Dynamics in the Human Respiratory System - page 266

m, 550 kg/m 3 . b 30 Fig. 8.25 Deposition patterns for 16 and 30 μ m pollen particles. a 16 μ μ m,

550 kg/m 3

Table 8.7 A comparison of particle deposition efficiency for 16 and 30 μ m pollen particles against

an aerodynamic equivalent sphere
Density

d p d ae Inertial Parameter (IP) Deposition Deposition

sphere (%) pollen (%)

550 16 11.86 23,443 30.3 19.9

550 30 22.25 82,500 86.0 66.2

This can be explained by the difference in the drag coefficient used for the non-
spherical shape of the pollen. Further analysis can be performed in the CFD software
by tracking the drag coefficient of the particle.
The drag coefficient comparison (Fig. 8.26 ) shows low drag coefficients for both
particles near the entrance of the airway, which steadily increases and reaches large
values near the nasopharynx. The increased drag coefficient assists in slowing down
the particle's momentum and thus reduces the required particle relaxation time (i.e.
Stokes number) the particle needs to complete the sudden changes of direction in
the flow field. From the drag coefficient Eqs. (8.11) and (8.18), it is apparent that a
relationship exists between the drag coefficient and the particle Reynolds number,
Re p , and this is visible in the opposing trendlines in Fig. 8.26 (i.e. where a peak in
the Re p is found, a corresponding low exists for the C d ).

8.3.3.3 Deposition of Fibres

MMVFs with a diameter of 3.66 mm, density at 1.83 g/cm 3 and varying lengths
were simulated through the left and right nasal cavities at a flow rate of 7.5 L/min