Evaporative cooling enhanced by fibrovascular capillary structures

Evaporation is a robust approach to removing heat from the human body, whereas evaporative cooling garments generally block the vapor diffusion from the skin resulting in discomfort. Inspired by the intensive evaporation of leaf stomata, some hydrophilic fibrovascular capillary structures incorporated with hydrophobic islands were proposed in this study, where the hydrophilic structures were designed for efficient water evaporation and the hydrophobic islands were used for the vapor diffusion from the skin to provide wetness comfort. Then, a numerical model was developed to investigate the evaporation characteristics of the hydrophilic surfaces with different fibrovascular capillary structures in indoor environments under different airflow directions with velocities from 0 to 0.4 m/s. The results showed that the fibrovascular capillary structures exhibited up to 80% higher evaporative mass/heat flux (i.e., per unit wet area) compared with the total hydrophilic surface due to the evaporation edge effect. Besides, the total evaporation rate with appropriate capillary branches even could be higher than that of a total hydrophilic surface under the vertical parallel flow. Furthermore, the horizontal parallel flow showed better evaporative performance than those under other airflow directions. Overall, with a small wet area, the fibrovascular structures could not only provide wetness comfort to the human body but could also offer similar or even higher evaporative cooling compared with the totally wet surface. Therefore, this work could contribute to advanced evaporative cooling garment design to provide people with thermal and wetness comfort, which is also important for electronic cooling and air ventilation design in buildings.