CFD-DEM simulation of capsule vibration facilitated powder discharge and dispersion in Breezhaler

This study presents a computational fluid dynamics-discrete element method (CFD-DEM) investigation on drug discharge and dispersion processes driven by capsule rotation and capsule-device collisions in Ultibro® Breezhaler®, where a layering dynamic mesh method is employed to characterize the capsule's complex rotational and vibrational motions, and a multi-scale model is adopted to evaluate the powder dispersion performance by predicting the fine particle fraction (FPF) based on carrier particle-wall collisions. The capsule vibration, either in continuous or intermittent regime, is found to effectively shake cohesive particles off the capsule wall, break particle clusters, and promote uniform particle distribution, facilitating complete drug discharge. Whereas, neglecting capsule vibration significantly underestimates the actual drug discharge efficiency. The particles inside the capsule and the rotation chamber are subjected to the strongest mechanical contact forces and aerodynamic forces with the former at least one order of magnitude greater than the latter. The capsule vibration is found to enhance both types of forces, particularly within the capsule. More importantly, capsule vibrations significantly increase the total number of particle-particle and particle-wall collisions in the inhaler, boosting the overall collision intensity relative to the none capsule vibration case. The predicted FPF_emitted values for cases incorporating either continuous or intermittent capsule vibration regimes show good agreement with the experimental data, while the value for the none capsule vibration case is markedly lower. This highlights the necessity of incorporating the capsule vibration into the CFD-DEM model and validates the applicability of multi-scale model for predicting powder dispersion performance in the Breezhaler®.