Case Studies in the Human Respiratory System - Computational Fluid and Particle Dynamics in the Human Respiratory System - page 252

of the particles via the nasal cavity. It is not surprising, then, that significant health
effects have resulted from direct contact of the inhaled wood dust with tissues of
the respiratory tract. While ingestion is also common, no health effects have been
reported.
In this case study, the application of spherical particles is applied to wood dust
inhalation, which has important implications for occupational injury to woodturners
who frequently encounter nose bleeds. Spherical particle modelling is quite common
because the assumption of a spherical particle allows a simplified drag correlation.
This advantage often outweighs the need to consider all the physics involved with
non-spherical particles, since approximate values can provide sufficient accuracy
for common engineering problems. Numerical simulations (Zhang et al. 2002, 2004,
2005b) have made use of spherical particles to represent the characteristics of general
particles.
Wood dust from pine (softwood) and from light and heavy oak (hardwood) was
simulated (Tian et al. 2007). The respective densities are 560, 590 and 930 kg/m 3 .
A study carried out by Chung et al. (2000) examined the particle size distribution
of dust during sawing and sanding of pine and oak. Oak dust generated by sawing
exhibited smaller particle sizes than the pine dust, while similar size distributions
were found for both pine and oak dust when generated by sanding. Therefore, only
nasal deposition of wood dust with size distributions from sawing will be investigated
herein. Figure 8.16 illustrates the measured and simulated particle size distribution
of both pine and oak. It is noted that the particle size distributions were based on the
particle number fraction and not volume fraction or mass fraction. Both heavy oak
dust and light oak dust were assumed to have the same size distribution. All particles
in this study were assumed to be spherical, which is not strictly true. However
for demonstration purposes, the spherical assumption is sufficient. Non-spherical
particles are treated in the next section.
Fig. 8.16 Simulated particle
size distribution and
measured particle size
distribution of dusts
generated by sawing. (From
Chung et al. 2000)