Comparison of micro- and nano-size particle depositions in a human upper airway model

Simulation results of microparticle and nanoparticle deposition patterns, local concentrations, and segmental averages are contrasted for a human upper airway model starting from the mouth to planar airway generation G3 under different inspiratory flow conditions. Specifically, using a commercial finite-volume software with user-supplied programs as a solver, the Euler-Euler (nanoparticles) or the Euler-Lagrange (microparticles) approach was employed with a low-Reynolds-number k-omega model for laminar-to-turbulent airflow and submodels for particle-phase randomization. The results show that depositions of both micro- and nano-size particles vary measurably in the human upper airways; however, the deposition distributions are much more uniform for nanoparticles. The maximum deposition enhancement factor, which is defined as the ratio of local to average deposition concentrations, ranges from about 40 to 2400 for microparticles and about 2 to 11 for nanoparticles with inspiratory flow rates in the range of 15 less than or equal to Q(in) less than or equal to 60 l/min. In addition, some airway bifurcations in generations G0 to G3 subjected to high inlet flow rates (say, Q(in) = 60 l/min) may receive only very small amounts of large micro-size particles (say, with aerodynamic diameter d(ae) greater than or equal to 10 mum) due to largely preferred upstream deposition. It has been hypothesized that, uniformly deposited nanoparticles of similar concentrations may have greater toxicity effects when compared to microparticles of the same material. (C) 2004 Elsevier Ltd. All rights reserved.