Performance analysis of a metal-hydride heat transformer for waste heat recovery

Metal-hydride systems are applicable as energy-conversion devices, such as cooling machines, heat pumps and heat transformers. Of particular interest are metal-hydride heat transformers, since they have more advantages over absorption or adsorption heat transformers for high-temperature boosting. Thus, growing attention has been given to metal-hydride heat transformers for the effective use of industrial waste heat. Thermal analysis on a module-type of metal-hydride heat transformer has been carried out to predict the performance of the system. The hydride reactor is considered as a coupled cylindrical tube module in the modelling. The effects of various operating conditions, as well as the design parameters, on the system performance have been extensively investigated. The optimal time of cycle period could be chosen from the numerical results, considering the performance. It is also found that the COP and heating output are increased as the waste-heat temperature is increased. The system performance could also be enhanced at the design phase by increasing the heat-transfer coefficient and the efficiency for internal heat exchange and by reducing the connection tube volume between reactors. The present results are also compared with the previous experimental results of metal-hydride heat transformers, as well as those of absorption heat transformers with LiBr-water. Copyright (C) 1996 Elsevier Science Ltd