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Abstract
Interest in pharmaceutical aerosol inhalation through respiratory airway is increasing as it is a fast and effective treatment for respiratory tract diseases. Dry powder inhalers (DPIs) are devices containing fine pharmaceutical powders which are aerosolized during patient’s inhalation and delivered into the distal part of the lung. However, existing DPIs have relatively low efficiency due to strong inter-particle cohesion caused by the small particle sizes (less than 5 microns). To improve DPI performance, both DPI devices and inter-particle forces need to be considered.
This work developed a CFD model, using ANSYS Fluent to simulate the fluid flow in a commercial inhaler Aerolizer®. The Discrete Phase Modelling (DPM) technique was adopted to track particle trajectories and depositions. The aim was to investigate the effect of DPI designs and electrostatic force on powder dispersion.
The particle-wall impaction has been demonstrated as the major mechanism of agglomerate breakage in DPIS. Thus, the original Aerolizer® device has been modified to add bumps inside the chamber. A series of CFD simulations were carried out to determine the effect of device design on particle dispersion performance. Sensitivity tests were conducted to examine the mesh independence of the model. The fluid flow and particle-wall impaction in the new design were compared with those in the original design. The simulation results showed that the existence of bumps directly affected the turbulence level generated in the device as it disturbed the fluid flow. This led to a reduction in the normal velocity of particle impaction and number of particle impactions. The axial velocities in mouthpieces were similar for both device designs. The fractions of particles escaped from the original device were 40%, 10% and 21% for 3 µm, 5 µm and 10 µm particles, respectively. Similarly, 55%, 47% and 22% of total particles escaped from the revised device.
The electrostatic force is one of the major adhesion forces during dispersion condition in DPI. Thus, the effect of electrostatic charge on particles was investigated during dispersion condition in DPIs. The well-established charge transfer theory was employed in CFD through Fluent UDF to determine the charge condition of fine powders during dispersion. The results showed that electrostatic charge distribution for escaped particles was lower for the revised device than the original device. Due to the large difference in magnitude between the van der Waals force and electrostatic force, the electrostatic force was found to have minimal effect on the particle dispersion. The overall particle-particle impactions were not significantly affected by the electrostatic force.
The study demonstrates the effects of device design and electrostatic force on particle dispersion performance providing further insight into optimising the DPI efficiency, which will provide a basis for the future improvement of DPI devices.