Numerical investigation of the dispersion in dry powder inhalers
Z.B. Tong1, B. Zheng1, R.Y. Yang1, A.B. Yu1 and H.K. Chan2
1 Laboratory for Simulation and Modelling of Particulate Systems, School of Materials Science and Engineering, UNSW Australia
2 Faculty of Pharmacy, University of Sydney, NSW, Australia
Inhalation aerosols offer the distinct advantage of rapid and convenient delivery of bioactive substances to the site of action. However, present pharmaceutical dry powder inhalers (DPIs) are extremely inefficient (only 10–30% of the stated dose reaches the lungs) and have large variability of dosing. This work investigates powder dispersion mechanisms in pharmaceutical dry powder inhalers, using the commercial Aerolizer® as a model inhaler device. A coupled CFD and DEM technique was adopted to simulate fluid flow and particles, respectively. The shear stress of turbulent flow had no visible effect on powder dispersion while the agglomerate-agglomerate interactions occurred only when the agglomerates were ejected from the capsule. Multiple major impactions occurred between the agglomerates and the chamber wall, which fragmented the agglomerates into large pieces without generating many fine particles. The subsequent impactions between the fragments with the grid were identified as the key factor for the dramatic increase in FPF. The inhaler was more efficient with increasing air flow rate in terms of the FPF, but its performance decreased at higher flow rates due to increased device retention.
(a) (b) (c)
Fig. 1. (a) Schematic view of Aerolizer inhalers; (b) fluid velocity; and (c) powder dispersion at v = 30m/s.