MEASUREMENT OF MOISTURE-TRANSFER THROUGH FABRICS BY THE HUMIDITY-GRADIENT METHOD

Abstract

Many methods for measuring fabric moisture-permeability are discussed. Usually, weighing method and water-level method are used to determine the rate of moisture-transfer in fabrics.
The applicability of the humidity-gradient method for measurement of moisture-transfer through fabrics was investigated in this paper and the following results are obtained:
(1) The humidity distributions close to water-surface and fabric-surface can be observed with the hygrometer.
(2) Regions of linear gradient of water-vapour pressure are found in water-surface and fabricsurface. These regions are considered as the diffusion layers, and the rates of water-evaporation are calculated from Fick's diffusion formula.
(3) Gradient of vapour-pressure, vapour-pressure on water-surface and effective thickness of diffusion layer estimated from the distribution curve of vapour-pressure near the water-surface depend on temperature, humidity and air velocity.
(4) The above three values depend on fabric moisture-transfer properties. The rates of fabric moisture-transfer obtaind from the humidity-gradient method and the weighing method are in a satisfactory agreement. So, it is concluded that fabric moisture-permeability can be measured by the humidity-gradient method.
(5) According to the humidity-gradient method, the diffusion coefficient of water-vapour in fabrics, the surface coefficient of fabric moisture-transfer and the total resistance of fabric moisturepermeability can be calculated.
(6) The effective thickness of diffusion layer is related to the surface constructions and materials of fabrics.