Permeability and thermal conductivity of porous metallic matrix hydride compacts

Abstract PMH compacts with various contents of aluminium matrix were prepared by a method including a final step of sintering under high hydrogen pressure. The gas permeability was determined as a function of the weight fraction of the aluminium matrix, ƒ. A correlation between the microstructure, morphology and porosity of the PMH compacts and the coefficient of permeability α′ was found. A tri-dimensional aluminium matrix was found to form in compacts having fractional aluminium contents in the range 0.15–0.22, and to be followed by a steep decrease of α′. On the other hand, the effective thermal conductivity k eff of the PMH compacts is known to increase with the increasing aluminium content. Major requirements from PMH compacts are high hydrogen and thermal yields, which are contingent upon high heat and mass transfer rates prevailing simultaneously. As the heat and mass transfer rates depend on k eff and α′ respectively, it is concluded that these quantities must be optimized in a range where k eff as well α′ are sufficiently high. The permeability results were interpreted also in terms of dimensionless parameters, such as the friction factor C f and Reynolds' number Re. From the results it is seen that the transition from the D'Arcy region to the high-velocity region is quite smooth and graduai as expected of porous materials.