Experimental and numerical investigations of moisture permeation through membranes

Experimental and numerical combined studies were carried out to investigate the effects of membrane properties and operating condition on water vapor (moisture) permeation through membranes. Experiments were conducted with water vapor transferring from a highly to a less humid air across membrane due to the water vapor concentration difference between the two sides of membrane, and numerical simulations were performed to simulate such process. The transmembrane moisture transfer was characterized using the moisture transfer resistance through membrane as well as the total moisture resistance, which include the membrane resistance and the boundary layer resistance on the two sides of membrane. The uniqueness of this research was a systematic examination of the effects of various membrane parameters and operating condition on the moisture permeation through membranes by combining the experiments and simulations. Tests were done on two membranes including the PVDF and PES membranes. The moisture diffusivities in these membranes were determined by comparing the experimental and numerical total moisture resistances. The results show that the moisture diffusivities in the PVDF and PES membranes are in the order of 10⁻⁶kgm⁻¹s⁻¹, with the PVDF yielding a larger diffusivity than the PES membrane. The moisture diffusivity in membrane, the maximum water uptake of membrane, and the sorption constant of membrane all have significant effects on the membrane resistance, with a high diffusivity, a large water uptake, and a proper sorption constant leading to a small membrane resistance, while the effects of the air entering humidity and airflow rate on the membrane resistance are dependent on the sorption constant. These results may help for the selection of the membrane materials.