Spatiotemporal sweat evaporation and evaporative cooling in thermal environments determined from wearable sensors

Highlights: • This study proposes a method for measuring human body evaporation. • Wireless wearable sensors and climatic observations are used for measurement. • Experiments verify the determination of spatiotemporal variations in evaporation. • Outcomes validate the method and its consistency with subjects' perception. • The proposed method can support human thermal evaluations under activity. -- Abstract: This study aimed to provide a mobile experimental method for assessing spatiotemporal skin evaporative losses that influence human thermal states. The proposed method can be used to predict the total evaporation from skin and corresponding evaporative heat loss by combining typical climatic observations and data from wearable sensors placed on the subject's skin over different anatomical regions. Wearable sensors can obtain humidity data, calculate local evaporation and local evaporative heat losses based on the theory of mass transfer, and then reflect the differences among individual physical characteristics. To validate the method, participants engaged in an experiment consisting of resting and a physical activity under three humidity levels. The results obtained from the proposed method are consistent with those from conventional whole-body weight measurements, thus demonstrating the effectiveness of the method to determine sweat evaporation. Furthermore, we evaluated the distribution of evaporation over the body during exercise and confirmed a reasonable agreement between the subjects' perception and the obtained thermal states. Overall, these results offer insights on the effect of thermal environments in practical situations entailing human activity. Likewise, we outline the application of the proposed method for predicting evaporation levels to assess human thermal environments.