MOVEMENT AND DEPOSITION OF FIBERS IN AN AIRWAY WITH STEADY VISCOUS-FLOW

Deposition of fibrous particles in lung airways is drastically differe nt from deposition of spherical particles because of aerodynamic diffe rences. In the past, assessment of fibrous particle deposition in airw ays used appropriate modifications of the analytical expressions for d eposition efficiency for spherical particles. Recently, Chen and Yu (1 991a) presented an analysis of fiber deposition by sedimentation for a parabolic flow through a circular tube. Fiber orientation in the Bow was obtained from Jeffery's equations (1922) adapted to the case of pa rabolic flow. Deposition efficiency was then found from the solution o f equations of motion for fibers. A more general approach has been tak en in this study, in which the flow field is arbitrary but at a low Re ynolds number. Inertial effects on both rotation and translation of th e fiber are neglected. Equations for fiber orientation are derived in terms of Euler angles phi and theta, and flow variables. The behavior of fiber orientation is found to be a function of the aspect ratio and initial orientation of the fiber, as well as the fluid strain and vor ticity. A set of equations is obtained that describes translation of f ibers in the flow field. Unlike the case of spherical particles, motio n of a fiber due to gravitational force can have a nonzero component i n all three coordinate directions. Fiber translation is a function of its geometry, its initial location and orientation, and a dimensionles s parameters tau(1) representing sedimentation. The differential equat ions of translation and rotation, which are coupled through the depend ence of fiber drag on its orientation in the flow field, are simultane ously solved numerically using a predictor-corrector method. For parab olic flow, the simulation results show that a for a given diameter, de position by sedimentation decreases as the aspect ratio increases. A s emiemperical expression is presented for tau(1) << 1, which relates fi ber deposition efficiency to tau(1), fiber aspect ratio, and airway in clination angle.