2018 Volume 32 Issue 1 Pages 132-139
Inhaled drug delivery is the most common treatment for respiratory disease today. The inhaled particles deposit mostly in upper respiratory even if they are aim to deposit in lower regions such as lung. Many previous studies have revealed that the Stokes number, which is the ratio of a characteristic time of the flow field Tf to the relaxation time of the particle Tp, well describes the deposition in upper respiratory tracts. However, most of the previous studies defined Tf as the ratio of the inlet diameter to the inlet velocity. This assumption oversimplifies a realistic flow field in an upper respiratory where the characteristic length and velocity greatly depends on the region. Here we propose a Stokes number, Stwall, in which Tf employs the inverse velocity gradient on the respiratory tract surface. As a result of our numerical simulation studies, we revealed that we can estimate the local deposition position with Stwall which can be calculated with the CFD of the airflows only. We also found that even the deposition fraction by the inertial impaction of particles of sinusoidal inflow rates can be well described with the impaction factor if it is weighted with the air inflow rate.
