Thermodynamics and kinetics analysis of hydrogen absorption in large-scale metal hydride reactor coupled to phase change material-metal foam-based latent heat storage system

Phase change materials (PCMs) have recently been coupled with metal hydride storage tanks (MHSTs) to store adsorption heat and subsequently deliver it for hydrogen desorption through melting and solidification cycles. This method might reduce process costs by eliminating the use of HTF (i.e. heat transfer fluid). However, thermodynamics and kinetic data are scarce for large-scale MH-PCM applications, particularly when PCM is loaded in metal foams (MFs) to promote heat transfer. The current work aimed to develop a 2D model for simulating H-2-absorption in a LaNi5-metal bed integrating a PCM-MF unit in a large-scale tube-and-shell heat exchanger. The constructed model (via Fluent 15.0 CFD-platform) was first-validated using referenced experimental data. The resulting heat transfer was analyzed for different MFs [aluminum, copper, nickel and titanium] of different porosities (0.1-1.0). Excellent outcomes were retrieved. By trapping the H-2-absorption heat, the MF-PCM unit improved the LaNi5 hydriding. The LaNi5 charging was achieved after similar to 500 s, independently of the MF type and porosity. The PCM melting rate depends on tube position, porosity and the MF type. It increased with MFs incorporation (order of enhancement: Cu > Al > Ni > Ti) and MF-porosity decrease (from epsilon = 100% to 10%). Besides, the PCM tube above the H-2-feeding pipe melts more quickly than the other tubes, presumably to the gravitational-force effect. Longer times (i.e. 9 000 s to >16 000 s, depending on tube position) were recorded for complete melting of the PCM when epsilon(MF) = 100%; however, when epsilon(MF) is less than 80%, the required time for total melting was tremendously reduced to less than 500 s. Nevertheless, the MFs porosity could not be decreased considerably to avoid a huge loss of material storage (PCM), thereby diminishing the thermal storage performance of the PCM matrix. (C) 2022 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

Automated summary

This study aims to develop a 2D model for simulating H-2 absorption in a LaNi5 metal bed integrating a PCM-MF unit in a large-scale tube-and-shell heat exchanger. The MF-PCM unit improves the LaNi5 hydriding by trapping the H-2 absorption heat. The type, porosity, and position of the MFs affect the melting rate and total melting time of PCM.