A novel mathematical model to predict the particle size distribution of pMDI aerosols

This paper presents a first principal approach to estimate the droplet size distribution of aerosols produced by a pMDI. Drug delivery efficacy of pMDIs is mainly governed by the droplet size distribution, so it is important to represent it accurately in the models as a function of time to estimate unwanted drug deposition. To estimate the temporal droplet size distribution, we propose a fundamental approach based on the numerical solution of the instability equation derived by Reitz and co-workers. This yields a distribution of fast-growing wave modes on liquid ligaments. In this work, the probability of production of droplets of a particular size is assumed to be equal to the computed growth rate of these wave modes. The slip velocity between the liquid and vapor phases is an adjustable parameter in the model. A comparison of the numerical predictions and results of phase Doppler anemometry experiments suggests that good agreement can be obtained for HFA134a and HFA227ea aerosols with minor adjustments of the slip velocity.