Hydrogen charging in AX21 activated carbon-PCM-metal foam-based industrial-scale reactor: Numerical analysis

Abstract

A computational fluid dynamics (CFD) model based on the mass, momentum, and energy conservation equations is used to simulate the industrial-scale hydrogen storage in activated carbon (AC: AX-21) bottle surrounded by a layer of metal foam (MF)-phase change material (PCM: RT 22 HC) latent thermal unit. The aim is to boost the recuperation (storage) of the heat liberated from the H₂‘s exothermic (adsorption). Following the model's validation, several numerical simulations were performed to evaluate the impact of various physical features of the MF (copper), at variable porosity (ε = 0.80–1.0), on heat transfer in the hole reactor. Independently of the MF porosity, the AC-bed temperature suddenly increased (from 295 K), reaching a maximum (at about 500 s) and decreased afterward. The temperature's intensity was dependent on the probe's position in the AC-bed (i.e. several positions were studied). The H2 concentration in the AC-bed may reach 25 mmol/g. The PCM-based unit received the discharged heat from the AC-bed slowly, but with PCM incorporation in MF, the heat was quickly recovered (stored). Thanks to the MF-induced PCM's increased thermal conductivity, the heat flux, the heat transfer coefficient, and the melting rate of the PCM were all accelerated (during the charging phase) several times by decreasing the MF porosity (increasing MF mass) from 1 (pure PCM) to 0.8. The temperature and the melting contours throughout the absorption process (up 10,000 s) supported all these findings. It is obvious from the results of the current study that improving the reactor geometry and the solid bed's thermal conductivity (thermal performance) is necessary for an effective hydrogen storage system.