Performances of metal hydride heat pumps operating under dynamic conditions

In this paper a procedure for the evaluation of the performance of metal hydride heat pumps under dynamic operation is presented. This procedure, based on a limited number of experimental results, allows the evaluation of the performance of coupled hydride beds, operating in heat pump mode (heat "upgrading" mode) or in refrigerant mode, for a wide range of working parameters of the cycle. The initial amount of hydrogen to be charged into the hydrides to obtain the maximum thermal power output may be also evaluated by this procedure. This allows the setting of the experimental apparatus to the most suitable initial conditions avoiding a large number of experimental tests. The procedure developed here has been applied to the LNA/MNA (LaNi4.7Al0.3/MmNi4.5Al0.5) hydrides operating in "upgrading" mode. The results of this application, which are in good agreement with the experimental results obtained by other authors [29-33], are presented and discussed. In particular the results show that the thermal power output attains a maximum value for a definite cycle time and for a definite hydrogen amount initially charged into the hydrides while the heat output and the efficiency always increase by lengthening the cycle time in consequence of the increase of hydrogen transfer. © 1989.