HEAT-STORAGE RATE OF MAGNESIUM NICKEL HYDRIDE

The heat storage rate of a single pellet of magnesium nickel hydride w as experimentally and theoretically studied for recovering waste heat from a industrial plant. The Mg-Ni hydride fine powder as a raw materi al was coated by copper thin film to obtain enough strength against hy drogen absorption/desorption cycles. The pellet was heated at a consta nt rate from roam temperature to 773 K and the heat storage rate of th e pellet due to thermal decomposition (1.08 Mg2NiH4-->1.08 Mg2NiH0.3+2 II(2)) was measured. Independently the properties of the pellet (therm al conductivity, specific heat, etc,) and intrinsic decomposition rate were determined, and then a mathematical model was proposed for simul ating the heat storage phenomena of the pellet. The decomposition rate was successfully estimated by a constant-temperature thermogravimetri c method with a rapidly heating apparatus. As a result, the thermal de composition began over 573 K at atmospheric pressure of hydrogen and i ts rate followed a first-order rate law. The computed decomposition cu rve of the pellet agreed with the measured one reasonably without any adjustable parameter, in which the heat storage rate of the pellet was controlled by the chemical reaction (decomposition) and heat transfer rates, not by the hydrogen diffusion rate. This work will be also uti lized For designing a packed bed unit for energy recovery/storage, cha rged with the pellets of a metallic-hydride forming alloy.