(403b) Modeling of Adsorbent Based Hydrogen Storage Systems

Adsorbent based hydrogen storage systems have high potential for meeting the DOE Technical System Targets for light vehicles. However, these systems must charge and be maintained at low temperatures to retain a useable quantity of hydrogen. Heat and mass transfer considerations for these low temperature systems, together with the thermodynamics of the adsorbent media, results in complex behavior that must be addressed for application to on-board vehicular storage. In general, the dynamic behavior of media based hydrogen storage systems is sufficiently complex that numerical models are required for evaluation and design. Numerical models suitable for engineering analyses of media based storage systems must couple the mass, momentum and energy conservation equations to the chemical kinetics equations, or isotherms, for the media as appropriate. Typically, for storage media having very rapid kinetics, state dependent models for isotherms along with mass transfer resistances are used to determine the amount and rate of hydrogen uptake or discharge.

This paper describes the application of numerical models to the evaluation of hydrogen storage systems that utilize MaxSorb MSC-30? and MOF-5? adsorbents. The models for these systems incorporate thermodynamic parameters obtained by fitting data to the Dubinin-Astakhov adsorption model. Non-ideal gas properties for hydrogen are required for the range of pressures and temperatures over which these systems operate. The models can be applied in up to 3 dimensions for arbitrary vessel geometries and boundary conditions. Validation is performed against experimental data for MaxSorb MSC-30?.

Designs for temperature control using heat transfer surfaces of various geometries and flow-through cooling by hydrogen gas are investigated. Effects of cooling methods and media compaction on charging rates, capacity, and system performance are assessed. High pressure systems, suitable for hybrid storage, in which a significant amount of hydrogen resides in inter-particle void spaces and pores, as well as in the adsorption volume, are considered.