Investigation of charged aerosol transport and deposition in human airway models

Abstract

Several theoretical and experimental studies of charged aerosol deposition in human airways have been reported. These studies suggest that higher charge values on particles lead to improve deposition efficiency in the human lung, especially in the alveolar region. Most of the previous numerical studies in realistic 3D geometrical models have been investigated only for uncharged particles. Hence, this research was aimed at numerically investigating aerosol transport and deposition by including the effect of electrostatic forces (both space and image charge forces). The numerical models that have been developed and presented in this thesis, treat the aerodynamics and electrodynamics as a coupled problem and successfully integrate both mechanisms. The physical model of the human lung used for this research consists of three sub-models: a 3D bifurcation airway model, a 3D reconstructed airway model representing the tracheobronchial region, and a 2D alveolar airway model representing the alveolar region. The airflow dynamics in these geometrical models were carried out using a Computational Fluid Dynamic software (CFD) with given boundary conditions related to corresponding breathing conditions. The space charge force was calculated using the Particle Mesh (PM) method, and the image charge force was computed using the mesh configuration. Both airflow dynamics and electrodynamics are integrated in the newly developed software, and the particle trajectories are then calculated. The numerical study of electrostatic forces is primarily focused on the submicron particle. The numerical study in the 3D tubular airway model gives a better understanding of parameters affecting the predicted deposition efficiency. The numerical study in the 3D tubular airway model focuses on the transport and deposition of particles near the branching regions between the parent and daughter tubes, where airflow profile is significantly altered, and secondary airflow also arises. Many charged particles are deposited near the carinae by the strong skewed axial velocity and image charge force. The space charge will influence the deposition efficiency if the number concentration of particles is high. Similarly, the charged particles in the 3D reconstructed airway model tends to have the deposition pattern near the branching regions, depending on the local airflow and charge value. In the 2D alveolar model, the image charge force can improve deposition efficiency. The outcome of this research clearly shows how the electrostatic forces play an important role in aerosol transport and deposition in human airways. The integrated numerical model provides a valuable tool for respiratory clinicians and the pharmaceutical industry to study the complex mechanism of drug aerosol deposition in human airways. Although this model is adequate for the intended purpose, it can be further improved by extending this work to develop a complete 3D model of entire human airways incorporating the full breathing cycle. Such a model would require extensive computing facilities, nevertheless it would be an enormous benefit to develop a better treatment for respiratory diseases.