Reijiro Takahashi

Optimization of microencapsulating and compacting conditions for hydrogen storage alloy

Abstract Thermophysical properties and cycling strength of a compact of copper-microencapsulated magnesium-nickel alloy have been studied for different fabrication conditions. In preparing the compact, the conditions of copper content (film thickness), loading pressure, loading hold time and pressing method were changed to assess their effect on thermal conductivity/diffusivity and strength against hydrogen absorption-desorption cycling. Thermal conductivity of the Cu-coated compact was shown to increase significantly compared with the Cu-free one; however, very significantly, thermal conductivity did not depend on copper content of the compact at all. Heavy loading pressure for compacting also increased thermal diffusivity due to an increase of contacted area among particles within the compact. However, the compact showed viscoelastic behavior; namely, it took as long as 1.8 ks until thermal diffusivity reached a constant value under a fixed loading pressure. Upon hydrogen absorption-desorption cycling the Cu-coated compacts did not crack, even after 200 cycles, while the Cu-free compacts broke easily within 100 cycles. These results show the possibility for the practical use of hydrogen storage alloy compacts with less copper microencapsulation.

Kinetics of hydrogen absorption and desorption of magnesium nickel alloy

Abstract Reaction rates in the Mg 2 NiH 2 system are still unclear, although they are needed for the process/optimization of hydrogen storage reactors. In this article, the rates of hydrogen absorption and desorption of the magnesium nickel alloy were investigated at different pressures up to 2.0 MPa using a constant-temperature thermogravimetric method. The powder of the alloy was microencapsulated with copper to improve the alloy properties (such as cycling strength) as a pretreatment. In the experiments, weight changes of the smallest amount possible of samples were monitored with the help of an ultra-accurate thermobalance, in order to avoid changes of the sample temperature due to the heat of the reaction. The reaction curves obtained revealed unique dependence of temperature and pressure and influence of thermal hysterisis. It is also possible that hydrogen-absorption and-desorption rates of this hydrogen storage alloy are expressed by the rate equation of first-order reversible reaction.

Prediction of Dynamic Two-Dimensional Behavior of Fine Powder Injected from Lateral Inlet into the Packed Bed

experimentally and theoretically studied, to understand fundamentally the phenomena in an ironmaking blast furnace with the injection of pulverized coal. Experimental results showed that holdup in the lower part of a packed bed around the inlets was more than 10 vol%, and was highly time-dependent and radially-distributed. In contrast, the holdup in the upper part of the packed bed was almost uniform, and was less than 1 vol%. A mathematical model was developed based on a continuous fluid model. The net deposition rate of powder was given by the difference between the adhering rate of powder and the departing one. Three constants, which correspond to the gravitational settling, the inertial deposition and the departing of powder, were included in the deposition rate equation of powder and were determined according to the measured result of transient pressure. By using the obtained equations, the model explained successfully measurements on holdup distributions.