(528a) Modeling of Combustion Wave Propagation in Heterogeneous Mixtures for Hydrogen Generation

We have recently proposed to use mixtures of boron-hydrogen compounds with metal powders and gelled water for hydrogen storage [1]. Due to the highly exothermic metal-water reaction, such mixtures, upon ignition, exhibit self-sustained propagation of combustion wave with simultaneous release of hydrogen from the boron compounds and water. In this work, we develop a numerical model for such a process in a solid fuel - water mixture. Production of a gaseous oxidizer (water vapor) in the combustion wave is a major feature of this model, which distinguishes it from previous developments for filtration combustion of powders and gas-generating systems. In the proposed model, the combustion wave structure includes a thin water-boiling front and a wide zone of reaction between the formed water vapor and porous solid phase. It is assumed that the combustion wave propagates uniformly and the equations are written in the moving coordinate system. The modeling provides the propagation velocity and thermal profile of the combustion wave for different kinetic parameters and fuel properties. Comparisons with available experimental data [1, 2] are made to improve knowledge of combustion mechanisms and reaction kinetics in the novel hydrogen-generating mixtures.

References

[1] Shafirovich, E., Diakov, V., and Varma A., ?Combustion ?assisted hydrolysis of sodium borohydride for hydrogen generation?, International Journal of Hydrogen Energy, Vol.32, 2007, pp. 207-211

[2] Diakov, V., Diwan, M., Shafirovich, E., and Varma, A., ?Mechanistic Studies of Combustion Stimulated Hydrogen Generation from Sodium Borohydride,? Chemical Engineering Science, in press, published on web 12/12/2006 (www.sciencedirect.com).

* Current address: Dipartimento di Ingegneria Chimica e Materiali, Università degli Studi di Cagliari, Piazza D'Armi, I-09123 Cagliari, Italy