Publications Details
Effects of metal hydride properties on the performance of hydrogen storage systems
Johnson, Terry A.; Dedrick, Daniel E.
Volumetric and gravimetric energy density are the primary performance metrics for the evaluation of automotive hydrogen storage systems. The purpose of this study was to determine the effects of material properties such as thermal conductivity, and thermodynamic properties such as enthalpy of formation on these energy densities. This was accomplished by first defining volumetric and gravimetric energy density in terms of global system parameters, followed by defining relationships between these upper level parameters and the more tangible hydride properties. These relationships were built using a generalized hydrogen storage system design and included structural and heat transfer calculations. The end result was a complex set of equations relating hydrogen storage system energy densities to the properties of the hydride contained in the system. These equations were solved for a range of metal hydride properties including effective capacity (amount of hydrogen per unit weight the metal hydride can absorb in a defined time period), material density, hydriding pressure, operating temperature, enthalpy of formation, thermal conductivity, and specific heat. The results show the relationship of these parameters to hydrogen storage system energy density. The combined effects of all variables in this multidimensional parameter space are presented as well as the isolated effect of each property on system volumetric and gravimetric energy density. The results indicate that while effective hydrogen capacity is the most influential metal hydride property, several other properties are nearly as important. Specifically, metal hydride enthalpy and density are revealed as key contributors to a viable hydrogen storage system. Also, the combination of specific heat and operating temperature is shown to be important when desorption heating is considered as a parasitic loss. Other metal hydride properties such as thermal conductivity and operating pressure are shown to be less significant. Copyright © 2007 MS&T'07®.