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TRANSPORT AND DEPOSITION OF NANO-SIZE PARTICLES IN THE UPPER HUMAN RESPIRATORY AIRWAYS
Citation:
Zhang, Z., C. Kleinstreuer, AND H. Shi. TRANSPORT AND DEPOSITION OF NANO-SIZE PARTICLES IN THE UPPER HUMAN RESPIRATORY AIRWAYS. Presented at American Asso. for Aerosol Research Conference, Los Angeles, CA, October 20-24, 2003.
Description:
TRANSPORT AND DEPOSITION OF NANO-SIZE PARTICLES IN THE UPPER HUMAN RESPIRATORY AIRWAYS. Zhe Zhang*, Huawei Shi, Clement Kleinstreuer, Department of Mechanical and Aerospace Engineering, North Carolina State University, Raleigh, NC 27695-7910; Chong S. Kim, National Health and Environmental Effects Research Laboratory, US EPA, Research Triangle Park, NC 27711.
Inhalation exposure to airborne ultrafine, i.e., nano-scale, particles or toxic gases and vapors can cause pulmonary and other diseases. In contrast, aerosolized drugs are now being orally administrated for medical treatment. Thus, it is important to understand the transport phenomena of ultrafine particles in the respiratory airways. Focusing on ultrafine particles in the 1 to 150nm diameter size range, where the dominant deposition mechanisms are convection-diffusion controlled, the 3-D airflow, fluid-particle dynamics, including deposition, are simulated and analyzed for different inspiratory flow conditions.
Specifically, using a commercial finite-volume software with user-supplied programs as a solver, the Euler-Euler approach for the fluid-particle dynamics is employed with: (i) a low-Reynolds-number k- model for laminar?to-turbulent airflow, and (ii) the mass transfer equation for dispersion of nano-particles. Presently, the upper respiratory system consists of two connected segments of a simplified human cast replica: (a) the oral airways, i.e., from the mouth to the trachea (Generation G0), and (b) upper bronchial tree models from G0 to G5.
The current simulation approach for the deposition of nano-particles due to diffusional transport has been validated with both analytical solutions in straight pipes and experimental data for a double bifurcation airway model. For the particle size range of 1-150nm and inspiratory flow rates of 125 ? 1000 ml/s, the simulated local particle deposition patterns are quantified in terms of local deposition fractions per unit area as well as deposition enhancement factors, which are defined as the ratio of local to average deposition densities. As with micro-size particles, deposition of nano-particles occurs to a greater extent around the carinal ridges when compared to the straight segments in the bronchial airways; however, deposition distributions are much more uniform along the airway branches. The deposition enhancement factors vary with bifurcation, particle size, and inhalation flow rate. Specifically, the local deposition is more uniformly distributed for large-size particles (say, dp=100nm) than for small-size particles (say, dp =1nm). The results suggest that computational techniques can successfully simulate transport phenomena of ultrafine particles in the human upper respiratory tract and provide detailed local deposition patterns useful for health risk assessment. This is an abstract of a proposed presentation and does not necessarily reflect EPA policy.