Numerical Simulations of Capillary Aerosol Generation: CFD Model Development and Comparisons with Experimental Data

Abstract

For a capillary aerosol generation system, the mechanisms governing droplet transport from the capillary tip through deposition in an enclosed geometry have not been previously explored. The objective of this study was to develop and validate a CFD model of transport and deposition for capillary-generated albuterol in water aerosols in a standard USP induction port used for pharmaceutical aerosol testing. Within this system, comparisons have been made between experimental measurements and numerical predictions of the jet angle, aerosol deposition in a sectioned induction port model, and size distributions of exiting particles. The CFD model employed accounts for multiscale and multicomponent flow initialized at the 57 μ m capillary tip and extending through the USP induction port with 30 L/min of co-flow air. A discrete Lagrangian particle tracking algorithm with corrections for near-wall anisotropic turbulence has been implemented to model the polydisperse particle phase including the effects of turbulent dispersion and evaporation. Results indicated good agreement between predictions of the numerical model and experimental in vitro measurements. The experimental mean (SD) total mass fraction of drug deposited in the sectioned induction port was 14.6 (1.1)%. Numerical predictions of deposited mass fraction for non-evaporating particles and evaporating droplets were 13.1% and 13.3%, respectively, resulting in relative differences of 10.3% and 8.9%. Comparisons between in vitro measurements and predictions within individual sections of the induction port resulted in relative differences as low at 0.75%. The predicted mass median diameters exiting the induction port for the particle and evaporating droplet models were 3.07 and 3.45 μ m, respectively, in comparison to an experimental value of 3.06 μ m. The numerical model developed in this study can be applied to optimize the capillary aerosol generation process and improve its delivery of aerosols to the lung.

Acknowledgments

This work was supported by Chrysalis Technologies, a division of Philip Morris USA. The authors are grateful for the critical advice of Kenneth Cox of Chrysalis and the help of Jeffrey Hinkins of VCU's Department of Mechanical Engineering for the design and fabrication of the sectioned USP induction port.

Notes

¹Mass of albuterol deposited expressed as a percentage of the theoretical delivered dose from the CAG.