Three-dimensional simulation of impinging jet atomization of soft mist inhalers using the hybrid VOF-DPM model

Impinging jet atomization is a new approach in inhalation therapy for drug delivery. Numerical simulation is a powerful tool for pursuing better understandings of the impinging jet dynamics. However, it is an extremely challenging task to simulate atomization of soft mist inhalers due to their complex nozzle geometry and spatial-temporal evolution of jets and droplets whose sizes span multiple orders of magnitude. In this work, the atomization process was simulated by a Computational Fluid Dynamics (CFD) model that couples the Volume of Fluid method (VOF), Discrete Phase Model (DPM), and Adaptive Mesh Refinement (AMR). A mapping approach was used to efficiently couple the liquid flow inside the small-scale nozzle with the large-scale multiphase jet flow outside the nozzle. The influence of flow field inside the nozzle on the atomization characteristics was explored. The numerical and experimental jet dynamics are consistent with regard to the plume geometry and particle size distribution. It was revealed that with the increase of the impingement angle and nozzle inlet pressure, the fluctuation of liquid sheet becomes more violent, which directly affects the breakup pattern and leads to much finer droplets. This method can be used to optimize the inhalers for better atomization performance.