An experimental set-up was designed and constructed to investigate the water vapor permeation through membranes.The test section mainly consisted of an airflow channel

a membrane

and a water tank

which formed a sandwich structure.The channel had a 5 mm×50 mm cross-section and a 800 mm length.Flowing in the channel was an air fluid with a low humidity.The membrane was sandwiched between the channel and water tank

forming an air gap with a higher humidity between the water and membrane.Moisture was transferred from the water to the air stream in the channel through the air gap and membrane.Tests were conducted on two membranes that included the PVDF (polyvinylidene fluoride) and PES (poly ether sulfone) membranes.The water vapor permeations through membranes were investigated.The membrane resistance was obtained by subtracting the convective moisture resistance in the channel and the moisture resistance caused by the air gap from the total moisture resistance.Through combination with the sorption curves of membranes

the diffusivities of moisture in membranes were estimated.The results showed that the diffusivities of the PVDF and PES membranes were in the order of 10-6 kg·m-1·s-1

and the former was about 4 times as great as the latter.