PARTICLE DIFFUSION FROM DEVELOPING FLOWS IN ROUGH-WALLED TUBES

A closed-form solution has been derived which quantitatively describes convective mass transfer in a conduit including wall irregularities a nd entrance effects. It permits the respective roles of the major diff usional parameters upon deposition to be formulated and examined direc tly. For testing, the model can be reduced to a limiting case; namely, the particle diffusion problem of Ingham (1991) for idealized (i.e., smooth-walled) short tubes. The mathematical model was used to study i nhaled aerosols in the upper airways of the human tracheobronchial tre e. We focused on the influences of core flow acceleration (in the lume n of an airway) and various cartilaginous ring structures (embedded in the surface of an airway). The effects of core flow acceleration on p article diffusion calculations were quite small for in vivo conditions . However, particle diffusion due to cartilaginous rings can be increa sed up to 32% relative to idealized tubes. The enhancement can be writ ten in terms of the airway surface function expressed as a power of th e ring shape aspect ratio h/b where h is the amplitude of the surface wave and b is its wavelength. (C) 1997 American Association for Aeroso l Research.