Abstract: The human body transfers water vapor to the outside environment by sweating. If water vapor fails to be transferred to the outside environment effectively, it will accumulate in the underwear air layer, resulting in increased humidity and human discomfort. The underwear air layer is affected by the skin surface curvature, fabric quality and clothing profile of various parts of the human body. The influence of its existence and thickness on water vapor transmission is relatively complicated. The research on the influence of underwear air layer on wet comfort is also relatively complicated. With the development of related instruments such as perspiration hot plate instrument and water vapor transmission tester, more and more studies have been done on heat transfer of fabric underwear air layer and water vapor transmission of enclosed air layer around. However, the opening air layer around the fabric also has a significant influence on the water vapor transfer performance of the fabric system, which is different from that of the closed air layer. At the same time, there is no corresponding instrument to detect the water vapor transfer performance of the fabric under the open state.
To study the water vapor transfer performance of fabric under the open state of the air layer around, we developed an instrument for measuring water vapor transmission of the fabric system with an open underwear air layer through the design and construction of auxiliary devices on the basis of M 261 fabric moisture permeability tester, and simulated the water vapor transmission rate of the fabric under different air layer thicknesses. On this basis, the corresponding analysis method was used to study the influence of the existence and thickness of the underwear air layer on the water vapor transmission rate of the fabric system. Specifically, under the condition of wind speed of 0.03 m/s, when the thickness of the underwear air layer is 4 mm, the water vapor transmission rate of the fabric system is lower than the water vapor transmission rate of the fabric. Under the condition of wind speed of 0.03 m/s, the water vapor transmission rate of the fabric system increases with the increase of underwear air layer thickness within a certain range. For ordinary clothing fabrics, the water vapor transmission rate of the fabric system reaches the maximum value when the thickness of the underwear air layer is 16 mm, which increases by 29.3% compared with the water vapor transmission rate of the fabric. For the waterproof permeable fabric with a low water vapor transmission rate, the water vapor transmission rate of the fabric system reaches the maximum when the underwear air layer thickness is 20 mm, and there is almost no difference with the water vapor transmission rate of the fabric system for ordinary fabric.
The simulated measurement of the water vapor transmission rate in the underwear air layer is closer to the actual wearing state. The water vapor transmission testing device and experimental method of the fabric system designed can provide reference for further research on the water vapor transmission testing in the underwear air layer.

Key words: fabric system, the thickness of underwear air layer, water vapor transfer performance, accessory device

摘要： 在M 261型织物透湿性能测试仪的基础上，通过设计和搭建辅助装置，实现了对具有开放的衣下空气层的织物系统的水汽传递性能的测试。利用该装置对8种织物进行了衣下空气层厚度分别为4、8、12、16 mm和20 mm时织物系统的水汽传递性能测试。结果表明：在风速为0.03 m/s的条件下，在一定范围内，织物系统的水汽传递率随着衣下空气层厚度的增大而增大；衣下空气层厚度为4 mm时，织物系统的水汽传递率低于织物的透湿率；衣下空气层厚度为16 mm时，对于普通织物，织物系统的水汽传递率达到最大，比织物的透湿率高29.3%；衣下空气层厚度为20 mm时，对于防水透湿织物，织物系统的水汽传递率达到最大，与普通织物相比，织物系统的水汽传递率几乎没有差异。

关键词: 织物系统, 衣下空气层厚度, 水汽传递性能, 辅助装置