Heat and mass transfer in footwear: Exploring the moisture evaporation and condensation cycle

This study investigates the movement of moisture and associated heat loss from the sock to the microclimate and external environment in mountain footwear. As it is not how much sweat is produced, but how much of it can evaporate, a thorough study was carried out to analyse the various contributions to heat exchange in this context. The tests were performed on a thermal manikin with a 100% cotton sock loaded with different amounts of water (0g, 5g, 15g, and 30g) at 10°C and 50% RH. Long-term tests were carried out with the maximum amount of water loaded (30g) to observe the different phases of heat and mass transfer until complete evaporation of all moisture (both from the socks and from the boots). In addition, evaporation tests were performed under semi-isothermal conditions (Tamb = Tman = Tsocks) at 34°C and 12% RH (same vapour pressure as in the cold tests) to isolate the evaporative contribution without any conductive, convective or condensing heat loss component. The actual effect of the evaporation was compared with the theoretical estimates from the mass-loss method. It was found that heat loss by evaporation was overestimated as a fraction of water evaporated from the socks underwent condensation in the boots, which does not contribute to cooling the system and returns heat to the system.