Effect of Fiber Geometry on Deposition in Small Airways of the Lung

ABSTRACT

The movement of a fiber in air is influenced by its orientation with respect to the direction of motion. Fiber orientation, in turn, depends on its geometry as well as the flow field. Due to the complexity involved in drag and torque calculations, straight fibers are represented in the earlier studies by an ellipsoid or a cylinder (for which there exist analytical expressions for fluid dynamic force and torque). However, real, natural, and industrial fibers are curly and irregular-shaped. A more realistic analysis of fiber deposition in lung airways should include the fiber geometry effects. A curved fiber may be modeled by the connection of many straight fiber segments. In this study, a curved fiber that is made of two ellipsoidal links attached at angle γ is considered. Using the expressions for drag force and torque for an ellipsoid, the total fluid dynamic forces and torques acting on a curved fiber were obtained. The equations governing the translation and rotation of a two-link fiber were solved, and the fiber deposition due to sedimentation losses in an airway was determined. Fiber movement was found to depend on its aspect ratio, curvature angle, and a sedimentation parameter. For a curved two-link fiber, there was no orderly movement in air, as was observed for a straight fiber. Increasing aspect ratio increased deposition, while increasing fiber curvature (decreasing angle γ) decreased deposition.