Flow of aerosol in 3D alveolated bifurcations: experimental measurements by Particle Image Velocimetry and Particle Tracking Velocimetry

Studies related to aerosol transport and deposition in the alveolar region of the lung have been mostly restricted to numerical studies, which require further experimental validation . Indeed, there are few experimental studies with quantitative data due to the complexity of measurements in extremely low Reynolds-numbers (in the order of 0.1) encountered in the lower lung airways. This article describes the experimental measurements performed in a model of multiple lung bifurcations with cylindrical cavities representing the alveoli. Both velocity field and aerosol trajectories were measured with Particle Image Velocimetry (PIV) and 3D Particle Tracking Velocimetry (PTV), respectively. Silicon oil was used as carrier fluid to satisfy Reynolds similarity. Small iron beads of 1.2 mm and 0.5 mm were used to simulate aerosols of 5.3 µm and 2 µm, respectively. Steady flow velocity distributions were measured by PIV using 20µm iron particles as tracers. The images were processed with an algorithm that used a combination of the advanced interrogation method with an ensemble averaging procedure. Displacement from 0.02 to 20 pixel were detected covering a velocity range of 0.02 to 10 mm/s. Two cameras were used in the PTV measurements to track the aerosol particles in three dimensions. All the particles trajectories were parallel to the bifurcation plane and only few 0.5 mm beads did not deposit inside the model. The trajectories deviated from the flow streamlines mainly under the effect of gravity. Finally, velocities measured by PIV were used in the equation describing small particle motions in Stokes flow and accurately predicted the particles trajectories measured by PTV. In conclusion, both the PIV and PTV techniques can reliably be used in future investigations of aerosol behavior in more complex acinar models