UC Irvine

As proton exchange membrane fuel cell technology advances, the need for hydrogen storage intensifies. Metal hydride alloys offer one potential solution. However, for metal hydride tanks to become a viable hydrogen storage option, the dynamic performance of practical tank geometries and configurations must be understood and incorporated into fuel cell system analyses. A dynamic, axially-symmetric, multi-nodal metal hydride tank model has been created in Matlab-Simulink® as an initial means of providing insight and analysis capabilities for the dynamic performance of commercially available metal hydride systems. Following the original work of Mayer et al. [Mayer U, Groll M, Supper W. Heat and mass transfer in metal hydride reaction beds: experimental and theoretical results. Journal of the Less-Common Metals 1987;131:235-44], this model employs first principles heat transfer and fluid flow mechanisms together with empirically derived reaction kinetics. Energy and mass balances are solved in cylindrical polar coordinates for a cylindrically shaped tank. The model tank temperature, heat release, and storage volume have been correlated to an actual metal hydride tank for static and transient absorption and desorption processes. A sensitivity analysis of the model was accomplished to identify governing physics and to identify techniques to lessen the computational burden for ease of use in a larger system model. The sensitivity analysis reveals the basis and justification for model simplifications that are selected. Results show that the detailed and simplified models both well predict observed stand-alone metal hydride tank dynamics, and an example of a reversible fuel cell system model incorporating each tank demonstrates the need for model simplification. © 2008 International Association for Hydrogen Energy.