Human re-inhalation ratio under typical conditions

Abstract

Inhaled air quality is directly related to occupants’ health and quality of life. In this study, a numerical breathing thermal manikin was employed, who breathed following a sinusoidal function, with 10 breathing cycles per minute. Each cycle was composed of three phases: 2.5 s inhalation, 2.5 s exhalation, and 1 s pause. The influence of pulmonary ventilation rate, breathing mode and breathing cycle period on the re-inhalation ratio were studied by computational fluid dynamics (CFD) technology in combination with the species transport model. It was found that increasing the pulmonary ventilation rate led to a lower re-inhalation ratio. The re-inhalation ratio is the largest with the value of 0.91%, when exhaled through the mouth and inhaled through the nose. The re-inhalation ratio was up to 23.9 % lower with a pause of 1 s in the breathing cycle than without pause. When the pulmonary ventilation rate increased from 6 L/min to 8 L/min, the re-inhalation ratio decreased from 0.91% to 0.71%. This information would be an important basis for the development of the human microenvironment control and technologies, including intelligent, personalized air supply devices, local air supply and exhaust methods, and other advanced ventilation and airflow technologies.