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Contributions of kinetic energy and viscous dissipation to airway resistance in pulmonary inspiratory and expiratory airflows in multiscale symmetric airway models with various bifurcation angles

[+] Author and Article Information
Sanghun Choi

Department of Mechanical Engineering, Kyungpook National University, Daegu 41566, Republic of Korea
s-choi@knu.ac.kr

Jiwoong Choi

IIHR-Hydroscience & EngineeringDepartment of Mechanical and Industrial Engineering The University of Iowa, Iowa City, Iowa 52242, USA
jiwoong-choi@uiowa.edu

Ching-Long Lin

IIHR-Hydroscience & EngineeringDepartment of Mechanical and Industrial Engineering The University of Iowa, Iowa City, Iowa 52242, USA
ching-long-lin@uiowa.edu

1Corresponding author.

ASME doi:10.1115/1.4038163 History: Received April 27, 2017; Revised September 26, 2017

Abstract

The aim of this study was to investigate and quantify contributions of kinetic energy and viscous dissipation to airway resistance during inspiration and expiration at various flow-rates in airway models of different bifurcation angles. We employed symmetric airway models up to the 20th generation with the following five different bifurcation angles at a tracheal flow-rate of 20 L/min: 15, 25, 35, 45 and 55 degrees. Thus, a total of 10 CFD simulations for both inspiration and expiration were conducted. Furthermore, we performed an additional four simulations with tracheal flow-rate values of 10 and 40 L/min for a bifurcation angle of 35 degree to study the effect of flow-rate on inspiration and expiration. Using an energy balance equation, we quantified contributions of the pressure drop associated with kinetic energy and viscous dissipation. Kinetic energy was found to be a key variable that explained the differences in airway resistance on inspiration and expiration. The total pressure drop and airway resistance were larger during expiration than inspiration, whereas wall shear stress and viscous dissipation were larger during inspiration than expiration. The dimensional analysis demonstrated that the coefficients of kinetic energy and viscous dissipation were strongly correlated with generation number. In addition, the viscous dissipation coefficient was significantly correlated with bifurcation angle and tracheal flow-rate. We performed multiple linear regressions to determine the coefficients of kinetic energy and viscous dissipation, which could be utilized to better estimate the pressure drop in broader ranges of successive bifurcation structures.

Copyright (c) 2017 by ASME
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