Prediction of convective heat transfer coefficient of human upper and lower airway surfaces in steady and unsteady breathing conditions

Bio-effluent and metabolic heat production from the human body and its breathing activity can strongly influence the microclimate around the body. On the other hand, local properties of the microclimate around the human body can also significantly affect the interaction between the body and the surrounding environment by way of local flow and heat transfer characteristics close to the body. Breathing is one of the most essential activities in our lives, and the basic functions of breathing include exchanging gases (supplying oxygen from ambient air and removing carbon dioxide from the blood) and exchanging heat and moisture (sensible and latent heat). As a consequence, human beings experience lifelong interaction with indoor environments via inhalation. In this study, two types of three-dimensional respiratory tract models were developed using computed tomography data of a healthy human males. Computational fluid dynamics simulations are performed to analyze the airflow and temperature distributions inside respiratory tract models under various breathing conditions. We used low-Reynolds-number-type k-ε model to predict airflow in the airway models. The flow pattern inside the viscous sub-layer and convective heat flux on the airway tissue surfaces and convective heat transfer coefficients were analyzed. Through this study, the numerical errors were successfully identical, so this discrepancy of two airway models were assumed due to the differences in airway geometries and reflected individual specificity. Averaged and local convective heat transfer coefficient distributions of the human airway were summarized as functions of breathing airflow rate.