### Abstract

Gas phase mass transfer coefficients for nitric oxide (NO), ethanol (EtOH), and water vapor (H_{2}O) were determined for typical conducting airway geometry and tracheal flows (5 × 10^{-5} and 5 × 10^{-4} m^{3} s^{-1}), by solving the steady-state two-dimensional diffusion equation. A constant absolute production rate with first order consumption reactions in pulmonary tissue was assumed for NO. For EtOH and H_{2}O, constant concentrations were assumed in the blood and tissue, respectively. Results, expressed in terms of the average Sherwood number (Sh), were correlated with the Peclet (Pe_{r}) number, and the length-to-diameter (L/D) ratio for each airway branch in terms of a lumped variable, Pe_{r}(L/D)^{n}. (Sh) increases as the solubility of the gas in tissue and blood increases. In addition, Sh passes through a minimum value at Pe_{r}(D/L)^{n} equal to approximately one when axial convection and diffusion have equal but opposite magnitudes. We conclude that Sh is not a monotonic function of Pe_{r}(L/D)^{n} within the entire airway tree and that it depends on the physical properties of the gas in the tissue. This conclusion contrasts with previous experimental and theoretical correlations.

Original language | English (US) |
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Pages (from-to) | 326-339 |

Number of pages | 14 |

Journal | Annals of Biomedical Engineering |

Volume | 27 |

Issue number | 3 |

DOIs | |

State | Published - Jan 1 1999 |

### Keywords

- Airways
- Bifurcation
- Diffusion
- Pulmonary
- Sherwood number
- Tubes

### ASJC Scopus subject areas

- Biomedical Engineering

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## Cite this

*Annals of Biomedical Engineering*,

*27*(3), 326-339. https://doi.org/10.1114/1.145