Abstract
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.
Highlights
Background and motivationThere is a significant need for advanced hydrogen storage technology to enable the use of proton exchange membrane fuel cells in many applications
The current work is motivated by the desire to develop an Regenerative Fuel Cells (RFC) system, including metal hydride hydrogen storage that is germane to military auxiliary power unit applications
Model results showed significant error compared to the experiment when using these literature values. It is unclear if this discrepancy is due to prior poisoning of the metal alloy, or to some other degradation phenomenon. This result clearly shows that tank degradation must be considered when designing actual systems, such as RFCs, that rely on metal hydride storage
Summary
There is a significant need for advanced hydrogen storage technology to enable the use of proton exchange membrane fuel cells in many applications. The current work is motivated by the desire to develop an RFC system, including metal hydride hydrogen storage that is germane to military auxiliary power unit applications. A fuel cell/electrolyzer system can theoretically achieve a better energy density than even state-of-the-art chemical batteries [4] This could benefit military applications that currently rely on lead–acid batteries for electrical storage, without violating the single fuel mandate. Model results showed significant error compared to the experiment when using these literature values It is unclear if this discrepancy is due to prior poisoning of the metal alloy, or to some other degradation phenomenon. This result clearly shows that tank degradation must be considered when designing actual systems, such as RFCs, that rely on metal hydride storage. Model results were greatly improved by determining entropy and enthalpy values experimentally
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