The effect of length and diameter on the deposition of fibrous aerosol in a model lung bifurcation

Abstract

Lung deposition of fibrous aerosol was studied by using a model of the third lung bifurcation with dimensions based on the symmetric model A of Weibel [Weibel, E. R. (1963) Morphometry of the Human Lung. Springer, Berlin]. The fibrous aerosols were introduced to the model at steady inspiratory flow conditions: volumetric flow rates in the parent tube were 31.3 and 62.5 cm 3 s −1. Glass fibres which deposited on the daughter tubes, and then escaped, were observed under a scanning electron microscope (SEM), they were divided into three groups according to their length range: 10–20 μm, 20–40 μm and 40–80 μm. The deposited fractions were calculated for each length. For parts of the fibres which deposited on, and escaped from, the tube both the length and diameter of each fibre were measured, and a joint length-diameter distribution of fibres was described by a bivariate lognormal distribution. The diameter distributions for each range of fibre length were used to determine the fractions of deposited fibres ranging from 0.6 to 2 μm in diameter. The results indicated that the deposited fractions increased as both the Stokes number for randomly-oriented fibres and the fibre length increased. In particular, deposited fractions of small diameter fibres were strongly influenced by their length. These tendencies agreed with the theoretical results predicted by Harris and Fraser [(1976) Am. Ind. Hyg. Assoc. J. 37, 73–89], but the deposited fractions were smaller.