Moisture transfer of the clothing–human body system during continuous sweating under radiant heat:

Mass transfer due to perspired moisture in a clothing system is critical for the understanding of thermo-physiology and thermal protection of a clothed body. Previous studies usually investigated moisture transfer without considering the effect of liquid sweating or external heat hazards. To understand the mechanisms of sweat evaporation, accumulation and dripping with continuous sweating under radiant heat, a multi-phase experiment was designed with a sweating Torso. The concept of clothed wettedness was proposed to understand sweat evaporation of the clothed body. Results showed that the evaporation rate of the clothed body increased with increasing perspiration rate and the rate increase can be explained by the material properties (e.g., material composition, hydrophilicity and evaporative resistance (Ret)), which affected the sweat accumulation ability. Results also demonstrated a dual relationship of Ret with the evaporation rate of the clothed body. Firstly, the evaporation rate was increased for greater Ret due to the higher moisture accumulation. Secondly, when Ret exceeded a certain value, the evaporation rate decreased with greater Ret due to the reduction in the mass transfer coefficient. For radiant heat exposure, evaporated sweat may condense on the skin surface, decreasing the evaporation rate and increasing the dripping rate. The sweat transfer process was also investigated in detail by the combined analysis of the sweat transfer rate and the evaporative cooling efficiency. This study provides insights into how continuous liquid sweat transfers and evaporates in the clothed body and its interaction with clothing material and environment radiant heat, contributing to the understanding of thermo-physiological burden and thermal protection of the clothed body with intensive activities.