Direct numerical simulation of heat transfer between moist air and a human body wearing an air-conditioned vest

Wearable cooling vest with electric fans has become increasingly popular given the rising risk of heat stress in outdoor environments. The fluidic motion of moist air driven by two cooling fans and the heat transfer in both human tissue and moist air were analyzed by using direct numerical simulation. A new semi-microscopic model originally developed in the cloud microphysics was introduced. It was found that as the fan wind velocity increased from 16 to 160 cm/s the relative humidity just above the skin approached that of the outer air and the skin temperature slowly decreased over time. On the other hand, the heat flux from body compartments to the skin responded quickly to increased airflow, attaining an equilibrium value that was determined by the latent heat released via sweat evaporation. For the relative humidity of 40% and 80µm sweat drop radius the skin temperature decreased by about 1°C being comparable to the outside temperature. Visualization of fields found that the temperature and heat flux near the skin mirrored streaks exhibited by strong airflow vortices near the skin. The dependency of heat transfer on the Reynolds number, the relative humidity of the outer air and the sweat drop size was analyzed. The airflow was essential to transfer the outside air with low humidity to the skin and to remove the evaporated water vapor from the skin. Both body heat dissipation and water mass loss increased as the Reynolds number rose and the ambient humidity fell.