Study of particle coagulation and deposition in the human respiratory tract

An Eulerian model combined with population balance equation was developed in this study to investigate the coagulation and deposition of polydisperse particles in the human respiratory tract. The mass and moment terms were incorporated into the model to capture the size-dependent particle dynamics such as inertial drift and diffusion deposition. Experiments were conducted using a three-dimensional (3D) printed human upper airway cast under different particle number concentration conditions. The simulation results reached a fair well agreement with the measurement data. The validated model was then applied to analyze the effect of coagulation on a sub micrometer particle size change and deposition fraction. It was predicted that the higher number concentration and longer residence time promoted particle coagulation. A fitting equation for predicting cigarette smoke particle size and number distribution as a function of residence time was provided. Over 90% of particle mass loss in the airway model was attributed to coagulation, with less than 10% due to deposition. The total deposition fraction of cigarette smoke particles was decreased, as the formation of larger particles from coagulation reduced the diffusion effect. However, regional deposition in the larynx was increased due to enhanced inertial impaction. The numerical method provided in this study addressed the limitations of semi-empirical or analytical formulas for deposition prediction, enabling coupled Eulerian simulations of coagulation and deposition in a three-dimensional respiratory tract model. It can also be extended to explore the effects of other aerosol physics that involved size changes, such as particle breakup and growth on the airway deposition within this framework.