Evaporation of sweat from sedentary man in humid environments

Abstract

Physiological and sensory responses were observed in four male subjects while they were seated on a balance. The chamber temperature always equaled mean skin (Tsk)(34–36 degrees C), thus eliminating all sensible heat transfer. Ambient water vapor pressure (Pa) was increased in steps from 10 to 40 Torr. Tests at air velocities from 0.1 to 2.4 m/s were conducted with subjects nude and clothed. Esophageal temperature (Tes) and Tsk, heat rate (HR) and weight loss (M) were measured throughout the 2.5-h tests. After each 25-min humidity step subjects recorded their warm discomfort, sensation of sweating, and thermal sensation. Results: Tsk, HR, and M were unaffected by humidity until critical Pa (P a crit) was reached above which M decreased and Tsk and HR increased rapidly. P a crit decreased with clothing and decreasing velocity. Tes remainded relatively constant throughout the tests. Sweating, discomfort and temperature sensations increased gradually with increasing Pa. Above P a crit sweating and discomfort sensations accelerated markedly. Mass transfer coefficients and clothing vapor conductance factors were evaluated. Skin wettedness at Pa crit decreased from 74% at 0.1 m/s to 35% at 2.4 m/s.