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Research Papers

# Flow and Particle Dispersion in a Pulmonary Alveolus—Part II: Effect of Gravity on Particle Transport

[+] Author and Article Information
Sudhaker Chhabra

Department of Mechanical Engineering, University of Delaware, Newark, DE 19716

Department of Mechanical Engineering, University of Delaware, Newark, DE 19716prasad@udel.edu

1

Corresponding author.

J Biomech Eng 132(5), 051010 (Mar 30, 2010) (8 pages) doi:10.1115/1.4001113 History: Received June 15, 2009; Revised January 13, 2010; Posted January 27, 2010; Published March 30, 2010; Online March 30, 2010

## Abstract

The acinar region of the human lung comprises about $300×106$ alveoli, which are responsible for gas exchange between the lung and the blood. As discussed in Part I (Chhabra and Prasad, “Flow and Particle Dispersion in a Pulmonary Alveolus—Part I: Velocity Measurements and Convective Particle Transport  ,” ASME J. Biomech. Eng., 132, p. 051009), the deposition of aerosols in the acinar region can either be detrimental to gas exchange (as in the case of harmful particulate matter) or beneficial (as in the case of inhalable pharmaceuticals). We measured the flow field inside an in-vitro model of a single alveolus mounted on a bronchiole and calculated the transport and deposition of massless particles in Part I. This paper focuses on the transport and deposition of finite-sized particles ranging from $0.25 μm$ to $4 μm$ under the combined influence of flow-induced advection (computed from velocity maps obtained by particle image velocimetry) and gravitational settling. Particles were introduced during the first inhalation cycle and their trajectories and deposition statistics were calculated for subsequent cycles for three different particle sizes ($0.25 μm$, $1 μm$, and $4 μm$) and three alveolar orientations. The key outcome of the study is that particles $≤0.25 μm$ follow the fluid streamlines quite closely, whereas midsize particles $(dp=1 μm)$ deviate to some extent from streamlines and exhibit complex trajectories. The motion of large particles $≥4 μm$ is dominated by gravitational settling and shows little effect of fluid advection. Additionally, small and midsize particles deposit at about two-thirds height in the alveolus irrespective of the gravitational orientation whereas the deposition of large particles is governed primarily by the orientation of the gravity vector.

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## Figures

Figure 1

Various gravity orientations for particle tracking

Figure 2

Particle maps for dp=0.25 μm and θ=0 after (a) 1, (b) 3, (c) 5, (d) 10, (e) 15, and (f) 20 breathing cycles

Figure 3

Particle maps for dp=1 μm and θ=0 after (a) 1, (b) 3, (c) 5, (d) 10, (e) 15, and (f) 20 breathing cycles

Figure 8

Particle maps for dp=4 μm and θ=π after (a) 1, (b) 2, and (c) 3 breathing cycles

Figure 9

Plots for particle (a) deposition, and (b) suspension for θ=π after multiple breathing cycles

Figure 10

Particle maps for dp=0.25 μm and θ=π/2 after (a) 1, (b) 3, (c) 5, (d) 10, (e) 15, and (f) 20 breathing cycles

Figure 11

Particle maps for dp=1 μm and θ=π/2 after (a) 1, (b) 3, (c) 5, (d) 10, (e) 15, and (f) 20 breathing cycles

Figure 12

Particle maps for dp=4 μm and θ=π/2 after (a) 1, (b) 2, and (c) 3 breathing cycles

Figure 13

Plots for particle (a) deposition and (b) suspension for θ=π/2 after multiple breathing cycles

Figure 14

Particle deposition efficiency (%) after 20 cycles as a function of particle size and gravity orientation

Figure 7

Particle maps for dp=1 μm and θ=π after (a) 1, (b) 3, (c) 5, (d) 10, (e) 15, and (f) 20 breathing cycles

Figure 6

Particle maps for dp=0.25 μm and θ=π after (a) 1, (b) 3, (c) 5, (d) 10, (e) 15, and (f) 20 breathing cycles

Figure 5

Plots for particle (a) deposition and (b) suspension for θ=0 after multiple breathing cycles

Figure 4

Particle maps for dp=4 μm and θ=0 after (a) 1, (b) 2, and (c) 3 breathing cycles

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