Case Studies in the Human Respiratory System - Computational Fluid and Particle Dynamics in the Human Respiratory System - page 247

The high flow rates found in regions A and A may be considered as undesirable
since it can lead to damage to the olfactory regions. Normally, low flow characteristics
are required in the olfactory region as it is a defence mechanism that prevents particles
whose trajectories are heavily dependent on flow patterns from being deposited onto
the sensitive olfactory nerve fibres, while vapours are allowed to diffuse for olfaction.
The turbinate region consists of a narrow, curled bone that protrudes into the main
airway. The middle and inferior turbinate are an important structure for filtration,
heating and humidification where the mucosal wall surface area is increased. How-
ever, only a small percentage of air reaches this outer surface area within the meatus
region ( F ). The surface area of the turbinates that is in contact with the airflow affects
less than2%oftheflowfield in terms of heating and humidification. This suggests
that the role of the turbinates to condition the air may not be solely reliant on the
surface area contact but may in fact be influenced by the nature of the flow that the
turbinates cause. The airflow distribution results obtained confirm this idea; however
further studies involving a larger sample of geometries are needed to confirm this
hypothesis.

8.2.8 Temperature Profiles

Temperature profiles were obtained from the averaged temperature at each cross-
section throughout the airway for a breathing rate of 10 L/min, so that comparisons
could be made with other data found in the literature. The results for the normal
air condition were compared with experimental work (Keck et al. 2000a, b) whose
results from a population of 50 and 23 volunteers, respectively, were averaged. The
profile showed good agreement in the frontal regions of the nasal airway, while a
small discrepancy is observed in the back regions towards the nasopharynx. The
profile converged to a steady value at a distance of 40 mm from the inlet, suggesting
that the air is conditioned early in the front region.
The profiles for the inhalation of cold dry air were recorded for the left and right
sides of the nasal cavity and also shown in (Fig. 8.13 ). The temperature profiles
converge to a peak value of 30.7 ◦ C for the last ten measurements away from the
inlet. This compares with the inhalation of normal air which has a value of 33.3 ◦ C
for the last ten measurements. The distance at which the profile converged to a steady
value is 71 mm from the inlet, which is the location where the left and right cavities
begin to merge together.
For normal air conditions, heating of the air is dominant in the frontal region of
the airway. The temperature difference is stable after the anterior turbinate region
and the heat transfer is minimal. One role of the highly vascularised turbinate region
that has been widely discussed is to condition the inhaled air. However, in the case
of normal air conditions, the turbinate region does not actually apply much heat
transfer but rather acts as a heat source through its constant temperature maintained
by the underlying capillary bed on the mucosal surface that provides the walls with
this energy. The majority of the temperature increases occur in the frontal regions
where the temperature difference is greatest. For the cold dry air case, the temperature