Computational analysis of geometrical factors affecting experimental data extracted from hydrogen permeation tests: I – Consequences of trapping

• Published in: International journal of hydrogen energy Vol. 36; no. 19; pp. 12644 - 12652
• Main Authors: Bouhattate, J., Legrand, E., Feaugas, X.
• Format: Journal Article
• Language: English
• Published: Kidlington Elsevier Ltd 01-09-2011; Elsevier
• Subjects: Alternative fuels. Production and utilization; Applied sciences; Computer simulation; Density; Diffusion; Diffusion coefficient; Energy; Exact sciences and technology; Finite element method; Fuels; Hydrogen; Mathematical analysis; Mathematical models; Membranes; Modelling; Permeation; Trapping; Trapping; Modelling; Diffusion; Hydrogen; Permeation; Evaluation; Experimental test; Desorption; Modeling; Geometry; Concentration measurement; Binding energy; Energy carrier; Membrane; Diffusion coefficient
• ISSN: 0360-3199; 1879-3487
• DOI: 10.1016/j.ijhydene.2011.06.143

Electrochemical permeation tests enable the experimental determination of the diffusion coefficient of a metal. To get a better understanding and a correction of experimental measures, we investigated the effects of hydrogen trapping on the diffusion of hydrogen through a metallic membrane by simulating a FEM model. The trap binding energy Δ
E
T ranges from −0.1 to −0.32
eV, the density of traps ranges between 10
−4 and 100
mol/m
3, and the thickness of the membrane fluctuates from 100
μm to 1
mm. It appears that the effective diffusion coefficient extracted from desorption flux data of a single membrane is not influenced by its geometry and depends on both the density of trapped hydrogen and the trap binding energy such as the apparent diffusion coefficient implemented in the code. Thus we do not detect any scale effect. In the other hand, the effective subsurface concentration evaluation using usually Fick’s laws doesn’t correspond directly to hydrogen concentration in the membrane. Analytical equations to solve the problem to extract erroneous data (diffusion coefficient and hydrogen concentration) to the experimental measurements of the flux
vs time curves have been proposed.
► We simulated permeation tests taking into account trapping of hydrogen. ► We treated the flux vs time curves as pseudo-experimental data. ► We examined changes between the FEM and the analytical parameters. ► We do not detect any scale effect. ► Analytical equations from the experimental measurements have been proposed.