HEAT-TRANSFER IN HYDRIDE PACKED-BEDS .2. A NEW EXPERIMENTAL-TECHNIQUE AND RESULTS ON LANI5 POWDER

In a former study [11] we pointed out the influence of the pressure and powder granulometry on the effective thermal conductivity, lambda(e), and the importance of the wall heat transfer coefficient, alpha(w). We have developed a new technique for measuring these parameters. Transient experiments (heating/cooling at constant hydrogen content) are performed in a small reactor. Lambda(e), and alpha(w) are yielded by identification with the help of a two-dimensional numerical model including a new phenomenological state equation for the LaNi5-H-2 system. The reactor, model and derived values of lambda(e) and alpha(w) for the LaNi5 powder under different hydrogen and argon pressures (1-2500 kPa) are presented. Their interpretation yields an estimate of the bulk LaNi5 thermal conductivity and some advices for improving heat transfer. In addition, the data on alpha(w) will permit optimizing exchangers design.