Heat and Water Vapor Transport in the Human Upper Airways at Hyperbaric Conditions

Abstract

Heat and mass transfer mechanisms have been characterized in physical models of human cadaver airways to simulated depths of 305 m with various gas mixtures. Such characterizations offer a detailed understanding of the effects of environmental pressures, gas composition, and respiratory rates (RMV) on the body cooling capacity of the respiratory airways. Empirical heat transfer relationships in the form -Nu = AReNPr1/3 are derived for the oral and nasal passageways during inhalation and exhalation flows. -Nu, Re, and Pr are the dimensionless Nusselt, Reynolds, and Prandtl numbers, respectively. The Nusselt and Reynolds numbers are based on the diameter and gas flow rate in the trachea and are applicable to Reynolds number values up to 70,000.

Derivation of Mass Transfer Coefficients for Transient Uptake and Tissue Disposition of Soluble and Reactive Vapors in Lung Airways

“…The procedure to calculate vapor concentration in the air and tissue phases were as follows: First, mass transfer coefficients given by Eqs. (16), (20), (21), (27), and (28) were used to find an overall mass transfer coefficient given by Eq. (7).…”

“…7 A similar finding was described by Miller et al 25 where they found a lower limit of Sh = 5.7 for convection-dominated flow and Sh = 8 for diffusion-dominated flow. Consequently, Bush et al 4 and Overton et al 30 made an adjustment to the model by Nuckols 27 for the lower limit of diminishing flow and proposed the following equation for the airphase mass transfer coefficient:…”

“…The air-phase mass transfer coefficient is related to physical determinants that yield airway losses and is a function of airway geometry, airflow velocity, and air-phase diffusivity. 2,22 It has been derived analytically for particles 5,16,32 and vapors 4,7,27,30 and is described further in the next section.…”

“…To be able to use Eqs. (16), (20), and (21) for pause and expressions (27) and (28) for exhalation, breathing times of pause and exhalation must be divided into many short intervals of time. Mass transfer coefficients and tissue concentrations must then be calculated during each time interval using the corresponding vapor concentration in the air (C a ) during that time interval.…”

Heat and Water Rate Transfer Processes in the Human Respiratory Tract at Various Altitudes

“…The "rst consists of the mouth and trachea; the second is the generations of the bronchial tree. Sherer & Hanna (1984) recommend the following heat transfer equation governing heat exchange process between inspired air and the surface of mouth/nose and trachea (Nuckols, 1981):…”