Effect of Feed Flow Rate of Hydrogen Mixture on Hydrogen Permeation for Flat Sheet Pd/Ag Membrane with Stagnating Flow

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The effect of feed flow rate of hydrogen mixture on the H2 permeation for a flat sheet Pd/Ag membrane with stagnating flow at the upstream side was investigated experimentally and theoretically. A 77wt.% Pd/23wt.% Ag flat sheet membrane with 25µm thickness and 0.02m diameter was used. The permeation rate of H2 was investigated under various feed flow rates (1.489 × 10<SUP>-5</SUP>-2.976 × 10<SUP>-4</SUP>mol/s), for pressures of 0.20-0.30MPa and reference membrane temperatures of 523-723K. Experimental results demonstrated that when the feed flow rate is decreased, the H2 permeation rate decreases. This is supposed to be due to the phenomena of hydrogen concentration decrease at the membrane surface of the upstream side, as a result of the effect of H2 permeation itself. When a theoretical equation that takes into account the effect of H2 permeation is used, the H2 permeation mole flux can be predicted quantitatively by using the concentration of H2 of the feed mixture. This shows that the diffusive transport effect plays an important role as well as the convective transport effect when determining H2 concentration at the membrane surface. In addition, the normalization of the theoretical results shows that the trend of the decrease in the H2 permeation mole flux with respect to the feed mole flux follows the first order lag function, regardless of the inlet H2 partial pressures.