Effective axial diffusion in an expansile alveolar duct model

Diffusion is described in an alveolar duct model, in which the following parameters are considered as variables: (1) ratio of lumen cross section to total cross section (s/S), (2) ratio of the diameter of the alveolar mouth opening to the mean alveolar width (AM/AW). A stochastic method is developed to determine a coefficient D*, which reflects the effective axial spread, for a wide range of (s/S) and (AM/AW). On the one hand, D* proves to be sensitive to (s/S); it is shown that the earlier suggestion to multiply the molecular diffusion coefficient by (s/S), slightly underestimated the effective axial spread. On the other hand, D* presents an extremely poor sensitivity to (AM/AW), in the range considered.