In order to study the heat and mass transfer in metal hydride reaction bed, the changes of pressure and temperature at each part of various reactors which have different interior structures each other, were investigated on hydrogen absorption or/and desorption.
The nature of resisitance of mass transfer through the reaction bed is hydrogen absorption by metal hydride due to rapid intrinsic kinetic rate, rather than the packing of powders which become more fine by pulverization during hydrogen absorption-desorption cyclings. Therefore, the role of filters in the reactors is not only providing the hydrogen transport path without impedence, but also enlarging the interfacial area between hydrogen gas and hydride bed to provide wider area where rapid hydriding reaction can occur.
The extent of enhancement of heat transfer in both reactors, with Al-foam skeletal structure and that with Cu-screen structure, was almost identical. From this result, it can be deduced that radial heat transfer, in the cylindrical reactor, is dominant in comparison with axial heat flow, and two dimensional radial improvements of heat transfer are necessary for the development of hydride chemical heat pump with high power and high efficiency.
Output and efficiency of heat pump composed of Al-foam type reactors which had shown best properties for heat and mass transfer, depended strongly on such operating conditions as the cycling time, temperatures of air blown, the amount of hydrogen gas with which the system was charged, and the flow rate of air blown to both reactors of heat pump. These effects of operating variables on the performance of heat pump can be explained by modified apparent kinetic equation.
