Modelling Drug Entrainment in a Dry Powder Inhaler: Benchmarking and Sensitivity Analysis of a Multiphase CFD Approach

Thomas Kopsch, Digby Symons, Darragh Murnane


Dry powder inhalers (DPIs) are used to deliver drug powder to the lungs. When a patient inhales through a DPI, air flows through the drug compartment and entrains drug. The rate of entrainment depends on a number of factors, including the inhalation flowrate, the geometry of the inhaler and physicochemical properties of the drug formulation. While the influence of each of these factors has been studied experimentally, a robust computational method to predict drug entrainment accurately for real world combinations of these parameters would be useful in the design and optimization of DPIs.

The objective of this study was to investigate the applicability of a multiphase computational fluid dynamics (CFD) simulation approach: Firstly, results of two different CFD solvers (ANSYS Fluent and OpenFOAM) were compared with experimental data. Secondly, the sensitivity of the drug release rate to variations of drug properties and CFD solver settings was investigated. Particularly, (a) the size of drug particles, (b) the density of particles, (c) the initial volume fraction, α, (d) the drag model, (e) the packing limit, αmax, and (f) the solids pressure were varied.

This investigation showed that the two different CFD solvers produced similar results and that these results were consistent with experimental data. The sensitivity analysis indicated that the simulated entrainment is not strongly dependant on either particle size or the choice of drag and solids pressure model. However, drug density, the initial volume fraction of drug, and the choice of the packing limit, do significantly influence the results.

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