A numerical simulation of air flow in the human respiratory system for various environmental conditions

Abstract

The functions of the nasal cavity are very important for maintaining the internal environment of the lungs since the inner walls of the nasal cavity control the temperature and saturation of the inhaled air with water vapor until the nasopharynx is reached. In this paper, three-dimensional computational studies of airflow transport in the models of the nasal cavity were carried out for the usual inspiratory velocity in various environmental conditions. Three-dimensional numerical results are compared with experimental data and calculations of other authors. Numerical results show that during normal breathing, the human nose copes with heat and relative moisture metabolism in order to balance the intra-alveolar conditions. It is also shown in this paper that a normal nose can maintain balance even in extreme conditions, for example, in cold and hot weather. The nasal cavity accelerates heat transfer by narrowing the air passages and swirls from the nasal concha walls of the inner cavity.

Keywords: Air flow in the human respiratory system; Alveolar state; Finite volume method; Heat transfer in the nasal cavity; Navier; Stokes equation.

Fig. 1

a-b Physical geometry of the studied area (all dimensions in mm), c the computational grid of a complex nasal cavity of a person.

Fig. 2

The 2D digitized cross-sections of 40 computed tomographic (CT) images of the respiratory tract of a healthy man

Fig. 3

Location of lines 1–4 at slices 1 and 2

Fig. 4

Comparison of the profiles of the horizontal velocity (U) component on lines 1–4 with the numerical results of other authors [28] and experimental data [11]

Fig. 5

The longitudinal components of the air flow rate in the nasal cavity. a-b three-dimensional distributions of the longitudinal components of the air flow rate with the deposition of streamlines, c the two-dimensional contours of the longitudinal components of the velocity of the cross section 1–3

Fig. 6

Two-dimensional and three-dimensional distributions of the longitudinal components of the flow rate for different environmental conditions: a-b at an ambient temperature of 25°C and humidity on the walls of the nasal cavity of 20% for different sections (sections 1-3). c-d at an ambient temperature of 5°C and humidity on the walls of the nasal cavity of 20% for different sections (sections 1-3). e-f at an ambient temperature of 5°C and humidity on the walls of the nasal cavity of 90% for different sections (sections 1-3). g-h at an ambient temperature of 40°C and humidity on the walls of the nasal cavity of 90% for different sections (sections 1-3). i-j at an ambient temperature of 25°C and humidity on the walls of the nasal cavity of 20% for different sections (sections 1-3). k-l at an ambient temperature of 5°C and humidity on the walls of the nasal cavity of 20% for different sections (sections 1-3). m-n at an ambient temperature of 5°C and humidity on the walls of the nasal cavity of 90% for different sections (sections 1-3). o-p at an ambient temperature of 40°C and humidity on the walls of the nasal cavity of 90% for different sections (sections 1-3). q-r at an ambient temperature of 25°C and humidity on the walls of the nasal cavity of 20% for different sections (sections 1-3). s-t at an ambient temperature of 5°C and humidity on the walls of the nasal cavity of 20% for different sections (sections 1-3). u-v at an ambient temperature of 5°C and humidity on the walls of the nasal cavity of 90% for different sections (sections 1-3). w-x at an ambient temperature of 40°C and humidity on the walls of the nasal cavity of 90% for different sections (sections 1-3).

Fig. 7

Comparison of temperature profiles (T) on lines 1–4 under different environmental conditions (for different ambient temperature and humidity on the walls of the nasal cavity: 1) 25 °C and 20%, 2) 5 °C and 20%, 3) 5 °C and 90%, 4) 40 °C and 90%)

Fig. 8

Comparison of concentration profiles on lines 1–4 under different environmental conditions