Deposition Characteristics of Aerosol Particles in Sequentially Bifurcating Airway Models

Local deposition efficiencies and deposition patterns of aerosol particles were studied experimentally in sequential double bifurcation tube models with two different branching geometries: one with in-plane (model A) and another with 90 out-of-plane bifurcation (model B). The dimensions of the model were similar to those of 3rd-5th generation human bronchial airways. Monodispersed oil particles (2.9-6.7 mu m diameter range) tagged with uranine were generated as test aerosols and were drawn through the model at flow rates in the Reynolds number (Re) of 283-4718. Both symmetric (1:1) and asymmetric (1:2, 1:3, and 1:0) flow patterns were used at the first bifurcation. Results showed that deposition efficiencies (DE) in each bifurcation increased with increasing Stokes number (Stk), ranging from ∼1% at Stk=0.02 to ∼40% at Stk=0.2, and could be fitted well with modified logistic functions. With symmetric flow conditions, DE was some what smaller in the second than the first bifurcation in both models. DE was greater in model B than model A in the second bifurcation. With asymmetric flows, DE was greater in the low-flow side compared to the high-flow side at a given Stk and this was consistent in both model A and model B. However, the average DE of the combined data for both the high- and low-flow side was similar to that with symmetric flows. Deposition pattern analysis showed highly localized deposition on and in the immediate vicinity of each bifurcation ridge at Stokes numbers as low as 0.02, regardless of branching patterns and flow distribution patterns used. These results showing detailed deposition characteristics in the sequential bifurcation geometry may prove useful for estimating local deposition dose in the airways and for developing improved lung dosimetry models.