A numerical and experimental study of spray dynamics in a simple throat model

Abstract

An inhalation airflow through a simple model of the human larynx and trachea, containing dispersed drug spray droplets, is studied numerically using the Computational Fluid Dynamics (CFD) code KIVA-3V (Amsden 1997) and experimentally using phase doppler interferometry. Flow conditions within the larynx and trachea affect the delivery of inhaled medications to the lungs. Deposition in these regions is considered undesirable and has been shown to be a particular problem for pediatric patients. The larynx geometry is represented by a constricted portion inside a straight tube. This constriction simulates the vocal folds within the larynx. The experimental model was 3.2 cm in diameter (approximately twice human scale) and 90 cm long. The constriction was 0.7 cm thick and was placed 30 cm from the inlet of the tube. The area of the constricted opening is approximately 40% of the tube area. Water droplets are introduced into the low-turbulence upstream airflow using a jet nebulizer. Measurements of axial velocity and axial turbulence intensity were made through an array of points between 2 diameters upstream and 4 diameters downstream of the constriction. Steady flows were used and the flow rates scaled to match in vivo tracheal Reynolds numbers simulating two different breathing conditions. The KIVA-3V code is specifically designed to analyze transient, two- and three-dimensional, chemically reactive fluid flows with sprays. The analysis considers spray dynamic effects such as coalescence, evaporation, deposition, and turbulent dispersion. The numeric simulation is carried out in a model consisting of a 21.7 cm long pipe simulating the measurement region. All other dimensions are identical to the experimental model. Several significant spray deposition mechanisms were notable in both the experimental and the numerical results.