Formulation of human body heat transfer coefficient under various ambient temperature, air speed and direction based on experiments and CFD

The purpose of this study is to confirm the effects of ambient temperature, airspeed, and wind direction on the heat transfer between human body and surrounding environment. First, a thermal manikin (TM) with fixed surface temperature (33 degrees C) was placed in a climate chamber with ambient temperatures of 20 degrees C, 24 degrees C, and 28 degrees C, at airspeed of under 0.1 m/s to confirm the effect of ambient temperature on heat transfer coefficient. In order to confirm effects of airspeed and wind direction, the same TM was then put in a wind tunnel with airspeeds ranging from 0.25 m/s to 1.4 m/s. The TM was set to face upwind, downwind, and perpendicular to the wind. Computational fluid dynamics (CFD) analysis was performed with conditions matching those of the experiment by using a computational TM with the same shape as that used in the experiment. In addition, numerical simulation of upward airflow condition and downward airflow condition in the standing posture with airspeed levels of 0.05-1.4 m/s was carried out. Higher ambient temperatures led to a decrease in the convective heat transfer coefficient and an increase in the radiative heat transfer coefficient. For airflows in the horizontal direction, whole-body convective heat transfer coefficient was the largest when the TM was facing downwind. For airflows in the vertical direction, the whole-body convective heat transfer coefficient for downward airflow was larger at airspeeds of 0.05-0.3 m/s. In contrast, when airspeed exceeded 0.3 m/s, the results were opposite.