A Numerical Model of the Combined Diffusion of Heat and Water Vapor Through Clothing

A model of combined heat and water vapor transport in multi-layered clothing is presented. Transport of heat by conduction and radiation and vapor transport by diffusion are included; heat and mass transport by forced convection are not. The calculations are performed in a time-dependent mode and compared to experiments performed on a sweating hot plate in a nonsteady state mode. Illustrative applications of the model and experiments display effects due to condensation and evaporation of water within the clothing and absorption and desorption by hygroscopic materials. Generally, it appears that all the observed heat loss from the hot plate can be explained in terms of the three mechanisms and the interactions between them. For the most part, the time-dependent treatment is necessary to understand the interactions. Water from sweat may accumulate within clothing because of condensation or absorption by hygroscopic materials and subsequently evaporate after the sweating has ceased. In both phases, the condensation, absorption, or evaporation substantially influences the heat loss. In the case of clothing that has been previously wetted by external means, the heat loss continuously changes as the clothing dries.