Hydrogen is being considered very seriously as an alternative, renewable energy carrier for use in internal combustion engines or fuel cells [Ritter et al, 2003]. However, despite some recent advancement, hydrogen storage is still a major concern. In addition to cost, safety and achieving sufficient gravimetric and volumetric densities, a hydrogen storage system, for both stationary and mobile applications, requires suitable thermal integration to facilitate optimal charging and discharging.

Among the commercially viable solid matrix methods of storing hydrogen, the complex hydride, NaAlH4, when doped with Ti, is one of the few, perhaps even the best, option for both stationary and mobile applications. The excitement about this system has been due to its relatively high gravimetric density and its reversibility at relatively low temperatures. However, a paucity of information is available on the design and development of hydrogen storage vessels containing complex hydrides.

The primary objective of this work is to further develop an existing 2-D mathematical model [Gadre et al, 2005; Wang et al, 2007a,b] to describe the dynamic behavior of a complex hydride hydrogen storage vessel during uncontrolled charge operations. This objective will be facilitated by drawing on the previous work by the authors on the modeling of more conventional metal hydride hydrogen storage vessels [Gadre et al., 2003; Jiang et al, 2005; Gadre et al, 2005; Wang et al, 2007a,b]. A secondary objective of this work is to study different ways of thermally integrating the hydrogen storage vessel, ranging from internal water or air heat exchangers, to external water or air heat exchangers. Again, this objective will be facilitated by drawing on the previous work by the authors on internal water heat exchanger vessel designs for metal hydride hydrogen storage vessels [Gadre et al., 2003; Jiang et al, 2005; Gadre et al, 2005; Wang et al, 2007a,b].

It is the contention here that the models developed by Ritter and co-workers for metal hydrides can be easily modified to explore the use of Ti-doped NaAlH4 as the reversible hydrogen storage media. Physical, thermodynamic and kinetic properties of Ti-doped NaAlH4, typically as a function of temperature and pressure, are needed. Some of this information is available in the literature, such as conductivity and heat capacities [Lesch et al., 2004; Wang et al., 2004], hydrogen storage capacities [Gross et al., 2002], charge and discharge kinetics [Bellosta von Colbe et al., 2005]. Some of it might have to be estimated. It is also the contention here that these models can be easily modified to explore different heat transfer modes. Different geometries for internal and external fluid heat exchangers will be readily programmed into the Comsol Physics software package, and different heat transfer coefficient correlations will be examined for the internal and external air heat exchanger configurations, such as finned geometries. This presentation will provide an up to date account of this model development effort being carried out for the design of a complex hydride hydrogen storage vessel.

Bellosta von Colbe, J. M., M. Felderhoff, B. Bogdanovic, F. Schueth, C. Weidenthaler, “One-Step Direct Synthesis of a Ti-Doped Sodium Alanate Hydrogen Storage Material, Chemical Communications, 37, 4732-4734 (2005).

Gadre, S. A., A. D. Ebner, S. A. Al-Muhtaseb and J. A. Ritter, “Practical Modeling of Metal Hydride Hydrogen Storage Systems,” Ind. Eng. Chem. Res., 42, 1713-1722 (2003).

Gadre S.A., A.D. Ebner and J.A. Ritter, “Two Dimensional Model for the Design of Metal Hydride Hydrogen Storage Systems,” Adsorption, 11, 871-876 (2005).

Gross, K.J., G.J. Thomas and C.M. Jensen, “Catalyzed Alanates for Hydrogen Storage”, J. Alloys Compd. 683-690 (2002)

Lesch, D A., Lewis G.J., Low, J.J., Sachtler, J.W.A., “Discovery of Novel Complex Metal Hydrides for Hydrogen Storage through Molecular Modeling and Combinatorial Methods” DOE FY 2004 progress report III.C.4

Jiang, Z., R.A. Dougal, S. Liu, S.A. Gadre, A.D. Ebner and J.A. Ritter, “Simulation of a Thermally-Coupled Metal Hydride Hydrogen Storage and Fuel Cell System,” J. Power Sources, 142, 92-102 (2005).

Ritter, J. A., A. D. Ebner, J. Wang and R. Zidan, R., “Implementing a Hydrogen Economy,” Materials Today, 9, 18-23 (2003).

Wang, J. et al., “Hydride Development for Hydrogen Storage”, DOE FY 2004 progress report III.C.2

Wang Y., A.D. Ebner and J.A. Ritter, “Thermal Characterization of a Metal Hydride Hydrogen Storage System with a Two Dimensional Model during Controlled Discharge,” Int. J. Hydro. Energy, to be submitted (2007a)

Wang Y., A.D. Ebner and J.A. Ritter, “Thermal Characterization of a Metal Hydride Hydrogen Storage System with a Two Dimensional Model during Rapid Charging,” in preparation (2007b).