Effect of design on the performance of a dry powder inhaler using computational fluid dynamics. Part 1: Grid structure and mouthpiece length.

This study investigates (1) the effect of modifying the design of a dry powder inhaler on the device performance, and (2) which design features significantly contribute to overall inhaler performance. Computational Fluid Dynamics (CFD) analysis was performed to determine how the flowfield generated in an Aerolizer at 60 l min(-1) varied when the inhaler grid and mouthpiece were modified. The computational models were validated by Laser Doppler Velocimetry (LDV). Dispersion performance of the modified inhalers was measured with a mannitol powder using a multistage liquid impinger at 60 l min(-1). The inhaler grid was found to significantly affect the performance of the Aerolizer. As the grid voidage was increased, the amount of powder retained in the device doubled (due to increased tangential flow of particles in the inhaler mouthpiece) and the FPF(Loaded) was reduced from 57 to 44% (due to increased mouthpiece retention). The length of the mouthpiece played a lesser role on the inhaler performance, having no significant effect on the flowfield generated in the devices. In summary, the performance of a dry powder inhaler can be affected by simple design changes. CFD, coupled with experimental results, provides a rational basis for understanding the performance difference.