Case Studies in the Human Respiratory System - Computational Fluid and Particle Dynamics in the Human Respiratory System - page 285

tangential
ports a

ligament
breakup

breakup
length

ligament
breakup

particle
formation

b

Fig. 8.43 Pressure swirl atomizer characteristics. a internal swirl chamber showing the tangential
ports within the atomizer and b atomization process

text by Lefebvre (1989) for further details. Although little has been researched on
nasal sprays, it is evident that the parameters that may influence nasal drug deposi-
tion include the spray cone angle, initial particle velocity, the insertion angle, and
swirl effects which will be evaluated for deposition efficiency under high and low
inertial particles. In addition to these parameters, the nozzle diameter, particle size
distribution, and break-up length may also have an influence.
The spray cone angle defines the degree of dispersion of the spray into the airway.
Studies have shown that the spray angle is influenced by the nozzle dimensions, up-
stream pressure, liquid properties and the density of the medium into which the liquid
is sprayed (Babu et al. 1982; Rizk and Lefebvre 1985). These design parameters can
be altered to achieve the desired spray cone angle. Therefore in the simulation, the
spray cone angle will be investigated to evaluate its performance. The diameter at the
break-up length is important in terms of particle initialisation in the computational
model as the particles need to be defined at the break-up length rather than at a point
located at the spray nozzle.
This can be approximated by

d bul = 2( d n + L bu tan φ ) (8.28)

where d bul is the diameter at the break-up length, φ is referred to as the half-cone
angle which is the angle between the spray sheet and the spray centreline, L bu is the