EFFECT OF FIBER GEOMETRY ON DEPOSITION IN SMALL AIRWAYS OF THE LUNG

The movement of a fiber in air is influenced by its orientation,vith r espect to the direction of motion. Fiber orientation, in turn, depends on its geometry as well as the flow field. Due to the complexity invo lved 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). Howe ver, real, natural, and industrial fibers are curly and irregular-shap ed. A more realistic analysis of fiber deposition in lung airways shou ld include the fiber geometry effects. A curved fiber may be modeled b y the connection of many straight fiber segments. In this study, a cur ved fiber that is made of two ellipsoidal links attached at angle gamm a is considered. Using the expressions for drag force and torque for a n ellipsoid, the total fluid dynamic forces and torques acting on a cu rved 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 w as found to depend on its aspect ratio, curvature angle, and a sedimen tation parameter. For a curved two-link fiber, there was no orderly mo vement in air, as was observed for a straight fiber. Increasing aspect ratio increased deposition, while increasing fiber curvature (decreas ing angle gamma) decreased deposition. (C) 1998 American Association f or Aerosol Research.