Use of Water Vapour Permeable Fabrics in Tents
DEFENCE RESEARCH ESTABLISHMENT OTTAWA (ONTARIO)
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The usefulness of a tent used in cold weather depends upon, among other things, the condensation of water vapor on the tent walls as this condensate can wet occupants insulating garments, increase the tent weight and increase the tents packed volume. In this report, the heat transfer and moisture transport across a single fabric layer as might occur in a tent is studied by means of mathematical models. The effects of water-vapour permeability of the fabric, interior air temperature and relative humidity and the ambient temperature on the condensation rate within the tent are examined. It was found that small decreases in the water-vapour permeability of the fabric layer can result in large increases in the condensation rate at the wall. Reducing the interior tent temperature or relative humidity can significantly reduce the condensation rate. The results indicate that a substantial portion of the water vapor within a very humid tent atmosphere escapes through the tent walls in all but the coldest ambient conditions for fabrics with low water-vapour resistance. A discussion is made regarding some of the advantages and disadvantages of using a single vapour permeable, waterproof fabric in place of more conventional arrangements with a permeable tent wall covered with an impermeable fly-sheet.
- Defense Systems