Simulation of Heat and Mass Transfer Processes in a Surrogate Bronchial System Developed for Hygroscopic Aerosol Studies

Abstract

In order to study quantitatively the behavior of inhaled hygroscopic aerosol particles, a surrogate tracheobronchial system, capable of simulating the in vivo atmosphere (i.e., temperature and relative humidity) in a physiologically realistic manner, was developed and is reported here. This surrogate tracheobronchial system is a tubular, multicomponent physical model in which the average Reynolds number value for the airflow within each respective compartment, or section, equals the value within the corresponding bronchial airway generation of Weibel's Model A network. The mass transport phenomenon (i.e., the in vivo water flow through a tracheobronchial wall and its membrane, and subsequent water evaporation into inhaled air) was simulated using this system. Detailed information regarding localized air temperature and water vapor concentration patterns for the steady flow rate of 13.5 L/min is reported in this work. The impact of the laryngeal simulator was studied, and average values of Nusselt and Shenvood numbers for each bronchial generation are reported. These values were lowest downstream from the laryngeal simulator.The in vitro temperature and water vapor concentration patterns and transfer coefficients will be used in a future quantitative analysis of the dynamic behavior and deposition rates of hygroscopic aerosol matter.

Development of a realistic human respiratory tract cast representing physiological thermal conditions

“…The temperature control feature of the cast was tested for uniform temperature distribution in the cast shell and maximum variation of 1 C was obtained using parallel connection of the cast segments to the thermal bath by flow splitter. We are also able to simulate the physiological temperature gradient with the temperature increasing from throat to deeper segments of the tracheobronchial system (Ferron, Haider, and Kreyling 1985;Eisner and Martonen 1989), since the water capillaries in different segments of the cast can be connected to heat sources with various temperatures.…”

“…Studies by Ferron, Haider, and Kreyling (1985), Eisner and Martonen (1989), Daviskas, Gonda, and Anderson (1990) used 1D mathematical models and experiments to evaluate the temperature distribution in the human tracheobronchial system. Ferron, Haider, and Kreyling (1985) approximated temperature and water vapor concentration in the human upper airways solving the 1D transport equations.…”

“…Daviskas, Gonda, and Anderson (1990) obtained the analytical solution for air flow temperature assuming a cylindrical geometry for different segments of the respiratory tract. Eisner and Martonen (1989) developed a surrogate tracheobronchial system with a multicomponent physical model, in which the average Reynolds number value for the airflow within each respective compartment equals the value within the corresponding bronchial airway generation of Weibel's model. They used the surrogate model to estimate the temperature in various segments of the surrogate bronchial system.…”

Effects of the ventilation pattern and pulmonary blood flow on lung heat transfer

“…Several models have been developed to characterize the conditioning of the inspired air by the bronchial tree (Daviscas et al 1990;Eisner 1989;George et al 1990;Hanna and Scherer 1986;Ingenito et al 1986;Ramm et al 1989;Tsu et al 1988). However, these studies have all concentrated on processes related to the inspired gas and do not provide results that allow the analysis of processes occurring during expiration in unsteady-state conditions.…”

Fluid Dynamics of the Human Larynx and Upper Tracheobronchial Airways

“…The casts were constructed from cadaveric larynges. Constricted tubes: Ferron (1977) and Eisner and Martonen (1989) Figures 2-4 indicate that the fluid dynamics situation at the glottal aperture is quite complex. Clearly, two pronounced events take place: (1) a laryngeal jet is created; and (2) flow separation occurs at the tips of the vocal folds.…”