Heat transfer and fluid flow analysis in a realistic 16-generation lung

Abstract

Heat transfer between inhaled hot/cool air and the lung surface within the human respiratory system is an intriguing topic that has not received enough attention. The lung can be considered as an in-vivo heat exchanger, balancing the inhaled air temperature by lowering the hot air temperature and increasing the cool air temperature. The current work studies the unsteady and incompressible airflow motion and heat transfer during inhalation between the surface of the lungs (37 ◦C) and the inhaled cool air (25 ◦C) in one case and inhaled hot air (43 ◦C) in another. Computerized tomography scan (CT-Scan) images of the lung were processed to generate the airway geometry consisting of 16 generations. The mesh generation was carried out using Ansys Meshing. The SST turbulent model was employed in Ansys Fluent 20.2 to model the air/lung convective volume heat transfer utilizing a realistic breathing velocity profile. Temperature streamlines, lung volume temperatures, surface heat flux, and surface temperatures on all 16 generations were produced for both cases during the breathing cycle of 4.75 s. Several conclusions were made by studying and comparing the two cases. First, heat transfer between inhaled hot or cool air and the lung surface mainly occurred in the first few generations. Second, airflow temperature patterns are dependent on the inlet breathing velocity profile. Third, the lung volume temperature change directly correlates to the temperature difference between air and the lung surface. Finally, the surface heat flux strongly depended on the heat transfer coefficient.

Numerical simulation of upper airway heat transfer in children with mandibular retrognathia during inspiratory process

“…A strong vortex region was visible in the oropharynx, which increased the heat exchange between the airflow and the oropharynx wall (10, 11). Besides, due to the presence of vortices, a more turbulent flow is generated, which leads to an increase in heat transfer with the airway surface (15).…”

“…Compared with the quiet breathing state, the heating capacity of the upper airway to the air was greatly reduced in the heavy breathing state, and the cold air stimulated the respiratory tract more in the heavy breathing state. Therefore, the temperature distribution of the airflow depended on the respiratory velocity distribution at the inlet, rather than the temperature difference between the air and the upper airway surface (15).…”

“…The SST k-ω turbulence model was used (15), and the pressure and momentum were discreteted in second order using the semiimplicit method of the pressure coupling equation. Normal air was used as the flow medium in the upper airway, and its physical characteristic parameters were as follows: ρ = 1.225 kg/m 3 ; k = 0.0242 W/(m•K); and the thermal conductivity is the same in all directions.…”