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DEPOSITION DISTRICUTION AMONG THE PARALLEL PATHWAYS IN THE HUMAN LUNG CONDUCTING AIRWAY STRUCTURE.
Citation:
Kim, C. S., Z. Zhang, AND C. Kleinstreuer. DEPOSITION DISTRICUTION AMONG THE PARALLEL PATHWAYS IN THE HUMAN LUNG CONDUCTING AIRWAY STRUCTURE. Presented at American Assoc. for Aerosol Research conference, Los Angeles, CA, October 20-24, 2003.
Description:
DEPOSITION DISTRIBUTION AMONG THE PARALLEL PATHWAYS IN THE HUMAN LUNG CONDUCTING AIRWAY STRUCTURE. Chong S. Kim*, USEPA National Health and Environmental Effects Research Lab. RTP, NC 27711; Z. Zhang and C. Kleinstreuer, Department of Mechanical and Aerospace Engineering, North Carolina State University, Raleigh, NC 27695
Inhaled particles deposit inhomogeneously in the lung and this may result in excessive deposition dose at local regions of the lung, particularly at the anatomic sites of bifurcations and junctions of the airways, which in turn leads to injuries to tissues and adverse biological effects. Besides the morphological factors, uneven and localized deposition occurs due to uneven airflow distributions among parallel airways: lung regions receiving greater airflow and particles will have greater deposition and vice versa. To examine the nature and extent of the uneven deposition distribution, we measured deposition patterns of monodisperse aerosols (3~5 m diameter range) in the three generation sequentially bifurcating airway models under various flow distribution conditions: symmetric flow (1:1 ratio at each bifurcation) and asymmetric flow distribution (1:2 and 1:3 ratio). Flow rate at the inlet of the model was in the range of 6-20 l/min, and Reynolds and Stokes numbers in the range of 606 - 4700 and 0.002 - 0.2, respectively. Deposition was determined by washing out deposited particles with distilled and deionized water section by section from the airway model and subsequently measuring fluorescent agent (uranine) tagged into the particles in the washed solution.
Because of the limited number of parallel pathways in the experimental model, 3-dimensional CFPD simulations were performed for 8-generation sequentially bifurcating airway models having 32 exit branches. This was achieved by first performing simulation work with 4-generation airway model and then continuing simulations with subsequent 4-generation model with input conditions that were equal to the exit conditions of the previous model. The CFPD model was previously developed for steady laminar inspiratory flow conditions using user-enhanced CFX software (AEA Technology) and thoroughly validated with various experimental data set. In the CFPD model the pressure at all exit branches were the same. However, because flow resistance was different among different pathways, this naturally developed uneven flow distributions among different pathways. Thus deposition values were obtained at each bifurcation with respect to flow rate, and the range of deposition variation among parallel branches was assessed.
Experimental results showed that deposition ratios between two parallel bifurcations ranged from 1.3 - 4.6 for the flow ratio of 1:2 and from 1.8 - 8.6 for flow ratio of 1:3. Deposition ratio was affected by both Reynolds and Stokes number. This indicates that deposition variation is much greater than expected from flow ratio. The CFPD results showed that deposition variation among parallel branches was in the range of 10 times whereas flow variation was within 3 times. The CFPD results also revealed complex particle trajectories intertwined with flow structures resulting in peculiar deposition patterns in the repeatedly bifurcating airway passage. In conclusions, particle deposition dose varies widely among the parallel airway passages and the variations take place due to a complex combination of airway morphology, flow patterns and particle properties. Thus, the average lung dose may significantly underestimate the potential health risk of particulate pollutant. The peak deposition dose at a local site may be a useful value to consider as a safeguard of the public health. This is an abstract of a proposed presentation and does not necessarily reflect EPA policy.