Modeling of the Time-Dependent H2 Emission and Equilibrium Time in H2-Enriched Polymers with Cylindrical, Spherical and Sheet Shapes and Comparisons with Experimental Investigations

Time-dependent emitted H-2 content modeling via a reliable diffusion analysis program was performed for H-2-enriched polymers under high pressure. Here, the emitted hydrogen concentration versus elapsed time was obtained at different diffusivities and volume dimensions for cylinder-, sphere- and sheet-shaped specimens. The desorption equilibrium time, defined as the time when the H-2 emission content is nearly saturated, was an essential factor for determining the periodic cyclic testing and high-pressure H-2 exposure effect. The equilibrium time in the desorption process was modeled. The equilibrium time revealed an exponential growth behavior with respect to the squared thickness and the squared diameter of the cylinder--shaped specimen, while it was proportional to the squared diameter for the sphere-shaped specimen and to the squared thickness for the sheet-shaped specimen. Linear relationships between the reciprocal equilibrium time and diffusivity were found for all shaped polymers. The modeling results were confirmed by analysis of the solutions using Fick's second diffusion law and were consistent with the experimental investigations. Numerical modeling provides a useful tool for predicting the time-dependent emitted H-2 behavior and desorption equilibrium time. With a known diffusivity, a complicated time-dependent emitted H-2 behavior with a multi-exponential form of an infinite series could also be predicted for the three shaped samples using a diffusion analysis program.