Efficiency of sweat evaporation in unacclimatized man working in a hot humid environment

SummaryA method is devised where evaporation and dripping sweat rates can be continuously determined during work. 6 unacclimatized men performed work on a bicycle ergometer at 3 different workloads and in 3 humidities. Ambient temperatures were always equal to mean skin temperatures, thus eliminating all sensible heat transfer. Evaporation rates ranged between 6.8 and 11.2 g · min−1. Rates of dripping sweat ranged from a mean of 2.2 to 10.4 g · min−1. One subject dripped 20.3 g · min−1 in condition H3 (70% RH, 100 W). The fully wet skin in condition H3 corresponded to an evaporative heat transfer coefficient of 99 W · m−2 kPa. Efficiency of sweating, defined as the ratio between secreted and evaporated sweat, ranged from 87 (50% RH, 50 W) to 51% (70% RH, 100 W). Corresponding values of wettedness were 0.56 and 1.0. Efficiency fell to 51% for fully wet skin (H3), and in some subjects the efficiency values were remarkably low. One subject displayed an efficiency of 31% in condition H3. The reduction in efficiency at a given level of wettedness was higher than previously reported.