Case Studies in the Human Respiratory System - Computational Fluid and Particle Dynamics in the Human Respiratory System - page 248

Fig. 8.13 Temperature
profiles across the nasal
cavity from the inlet. The
solid black line represents a
normal inhalation condition
compared with experimental
work. The colourless symbols
represent the simulated
results for cold dry air

35

30

25

20

Keck et al. 2000a
Keck et al. 2000b
CFD_normal
CFD_cda-left
CFD_cda-right

15

10

0 20 40 60 80 100

X- Distance From Nostril Inlet [mm]

profile follows a similar curve, but shifts downward to accommodate the temperature
decrease.
Given that other dependent variables, such as wall temperature and a steady air
flow, were kept constant in this study, the effects of the differences in nasal morphol-
ogy and hence the differences in the flow field could be isolated for analysis. The
averaged temperatures at different cross-sections shown in Fig. 8.14 were recorded
and compared. The left cavity produces higher temperatures in the front regions be-
fore the airway expands just after cross-section B ( x 19 mm); however after the

airway expansion the right cavity produces higher values.
The contour plots reveal that the cooler air is found at the central locations of
each cross section furthest from the wall. The temperatures at the olfactory regions
(top of sections D and E) remain high because little airflow reaches this upper region
and the region is heated by the close surrounding walls. This is an important feature
of the human body as the olfactory epithelium is lined with delicate olfactory receptor
neurons which need to be void of any cold dry air exposure to prevent any damage. At
section C, the left-side is thinner; however the bulk of the flow remains in the middle
region which accelerates through. The bulk flow regions are the last to be heated up
to a peak value of 30.7 ◦ C. A comparison of the temperature contour plots in Fig. 8.14
with the axial velocity contours in Fig. 8.8 shows that at high axial velocity regions,
the temperature is at its lowest. This is due to the finite heat source provided by the
constant wall temperature where the heating of the cold air is dependent on the mass
flow rate as depicted by the thermodynamic balance equation:

≈

Q

=˙ mC p ( T wall − T air ) (8.8)

This implies that the flow residence time m is critical for the inhaled air to be heated,

given that the heat source is driven by the difference in the constant wall temperature
and the inhaled air.

˙