Assessment and Analysis of the Bellows Ventilation of Clothing

Abstract

A methodical approach is described, attempting to separate the loss of heat and moisture due to forced exchange of air inside clothing, when walking, from the loss caused by gradients between the body and the environment.Temperature, heat flow, and relative humidity were recorded on the skin of the back and inside the respective clothing (shirt only, vest and shirt, or vest, shirt and anorak) in 12 experiments performed in a climatic chamber at 4-11°C and 35-70% RH, The subject walked on a treadmill with 5% grade at 7.2 km/hr until a new steady state of higher tempera ture and heat flow, as well as humidity, resulting from evaporation of sweat, was reached. When the motion was suddenly stopped, both the temperature and humidity increased steeply, while the heat flow decreased, showing levels which would have been attained, theoretically, if the transfer of heat and water vapor along gradients was not assisted by forced exchange of air when walking. When walking was resumed after a pause, all recorded parameters changed in the opposite direction. Continuous recording of temperature next to skin showed temperature oscillations synchronous either with every step or with every other step.The results are considered as evidence of the effect of forced ventilation on the microclimate. Calculated from changes in water-vapor pressure, the magnitude of forced ventilation corresponded, approximately, to dilution of the air layer next to skin, with atmospheric air, by one-half of its volume.It was demonstrated, in addition, that the heat of sorption, arising from transient increases of humidity in the clothing, had a marked effect on temperature of the micro-climate.The term "bellows ventilation" is thought to express best the mechanism of exchange of air resulting from rhythmical movements of limbs and body at physical activity.