CFD modelling of air flow and fine powder deposition in the respiratory tract

Abstract

This project was to investigate and observe characteristics of micro particles suspended in the ambient air or pharmaceutical aerosols with respect to the mechanisms of deposition in human airways under different inspiratory conditions. Such determination includes pattern observations of inspiratory flow-field of the air, particle trajectory during inspiratory conditions and particle deposition. Computational fluid dynamic (CFD) was employed to simulate above problems, aiming to observe flow-field of the inspiratory air and characteristic of flow turbulence in the respiratory tract as well as particle behaviour in the respiratory tract regarding to the particle deposition. In order to do so, three different airway models were employed for the simulations: two realistic airway models introduced by Kitaoka and Weibel airways model. The motion of micro-sized particles between 1~20 μm were simulated under the steady state two inlet-inspiratory conditions – inhalation condition (60 L/min) and breathing condition (18 L/min); to evaluate deposition efficiency. Inertial impaction was dominantly caused high density deposition of particles in upper tracheobronchial region, particularly in regions where daughter airways bifurcate. Results also showed that the velocity in the first bifurcation of airway was higher than the inlet velocity. Back pressures were been observed in lower generations, and high pressures were been observed at every bifurcation regions. The increase of velocity was observed where the fluid directions rapidly changed. Turbulence kinetic energy was the least in main bronchus of respiratory tract and fluctuated from generation to generation. In Kitaoka’s generation 0-7 model, deposition fractions of 2 μm, 6 μm and 10 μm particles were 6.6%, 60.7% and 91.5% respectively under inhalation condition whereas deposition fractions of such particles were 2.9%, 9.0% and 44.9% under breathing condition. In Kitaoka’s generation 0-11 model, deposition fractions of 2 μm, 6 μm and 10 μm particles were 30.9%, 80.1% and 99.8% respectively under inhalation condition whereas deposition fractions of such particles were 16.2%, 24.4% and 62.6% under breathing condition. Furthermore in Weibel’s generation 3-6 model, deposition fractions of 2 μm, 6 μm and 10 μm particles were 9.7%, 38.3% and 97.4% respectively under inhalation condition whereas deposition fractions of such particles were 3.2%, 15.6% and 56.2% under breathing condition