Study on the method for testing the water vapor diffusion resistance of membranes

Water vapor diffusion resistance is an important property of porous membranes. In the paper, a new apparatus for specially measuring the water vapor diffusion resistance of porous membranes was developed. In the new apparatus, the humidity of circulating carrier air streams flowing over both sides of test membrane are controlled by different saturated salt solutions, which makes a variety of humidity conditions and improves the humidity stability. In order to decrease the error caused by the air boundary layer, the structure of the test chamber was optimized with the help of computational fluid dynamics technology. Seven types of porous membranes with stable moisture permeability were tested by the new apparatus at relative humidity gradients of 0.42, 0.45, 0.51, 0.55, 0.64, 0.69, 0.73 and 0.78 across the porous membranes at 25 °C. The results of the new apparatus were compared with the results of nitrogen carrier apparatus and ISO 2528. The maximum relative errors of the new apparatus and the nitrogen carrier apparatus compared to the ISO 2528 method are 22.3% and 19%, respectively. The test results of the three methods are in good agreement. The new apparatus is a simple, low-cost and time-saving alternative for measuring the water vapor diffusion resistance of porous membranes.