大气低层的水汽量在干燥地区（量）甚微，而在潮湿地区按体积占4%左右。
Water vapor in the lower atmosphere can vary in amount from a mere trace in arid regions to about 4% by volume in moist areas.
干燥中所需空气的体积——将热传给食品使所含水分汽化所需要的空气量要多于将蒸汽运走离开干燥室所需要的空气量。
Volume of air required in Drying-More air is required to conduct heat to the food to evaporate the water present than is needed to transport the vapor from the chamber.
干燥空气是多种气体的混合，按体积计，大部分是氮气。
Dry air is a mixture of gases, most of which is nitrogen by volume.
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