Use of a Wetted Cover to Reduce Heat Stress in Impermeable Clothing

摘要

A mathematical model based on physical relations for heat exchange between clothed man and his environment has been developed which describes the cooling effect of a wet cover worn over an impermeable ensemble, in terms of the ensemble characteristics and the ambient environment. The model has been validated at low air movement for one such ensemble by comparing predictions of increased skin heat loss and cover evaporation with values obtained using an electrically heated copper manikin dressed in the ensemble, with the cover both dry and wetted. The model predicts for this ensemble supplementary cooling (increased skin heat loss) ranging from 40 watts at 35 degrees C, 70% relative humidity, and low air movement to almost 200 watts for a hot/dry environment of 50 degrees C, 20% r.h., with 5 meters/second wind. Predicted water requirements to maintain the cover wet under these conditions range from 0.2 kilograms/hr to 1.9 kilograms/hr. The model also reveals that the wet cover would reduce the heat load imposed on a man by sunlight by 20 to 40 watts in full sun, but with a 0.2 to 0.3 kilograms/hr increase in water requirements. (Author)