Best Practice Advice AC7-01
Aerosol deposition in the human upper airways
Application Challenge AC7-01 © copyright ERCOFTAC 2019
Best Practice Advice
Key Fluid Physics and Deposition Mechanisms
Airflow in the human upper airways transitions to turbulence due to geometric effects, such as the bent in the oropharyngeal region and the constriction at the glottis. The bent in the oropharynx causes substantial filtering of inhaled aerosols due to inertial impaction on the airway walls. Filtering in the extrathoracic airways increases as the particle size and inhalation flowrate increase.
As we move in the tracheobronchial airways, the Reynolds number is reduced because the air travels through a larger total cross-sectional area. As a result, airflow relaminarizes in the first generations. At the flowrate examined in the present AC, the main deposition mechanism in this region is inertial impaction, with significant deposition at the bents and the bifurcations. At lower flowrates, deposition can also be influenced by gravitational sedimentation because the residence times of the particles in the bronchial airways is longer.
Application Uncertainties
The differences between measurements and simulations can result from several uncertainties involved in the tests. A first source of uncertainty are the in vitm inlet conditions, which might be different from the velocity and particle profiles assumed in the CFD simulations. In the experimental setup, various devices were placed upstream of the mouth inlet (see figure 5 and these devices are expected to alter the inlet flow and particle conditions from what is prescribed in the simulations.
Another source of uncertainty between the experiment and the simulations is the size
of the particles. Monodisperse particles have been assumed in the simulations whereas the
aerosols generated in the experiments had a standard geometric deviation of size smaller
than 1.24μm.
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