Modelling and simulation of heating/airconditioning systems using the multi-hydride-thermal-wave concept

A computer code describing a transient model was developed to analyse the performance of a metal hydride heating/air-conditioning system. The model considers the effects of heat transfer by conduction in the metal hydride reaction beds, conduction-convection in the heat transfer fluid, hydrogen flow governed by Darcy's law and gas consumption by sorption kinetics. The model was applied to simulate two different concepts of fast reaction beds in the heating/air-conditioning device, using a novel capillary tube bundle reactor (CTBR) for improved heat transfer characteristics and the established metal foam tube reactor (MFTR), respectively. The reactors are equipped with cascades of different metal hydrides thus implying a moving thermal wave during operation. Numerical techniques were used to predict the liquid temperatures, solid phase temperatures, specific gas flow rates, hydrogen pore pressures and metal hydride compositions. A high performance of the devices was obtained by choosing optimized physicochemical and thermodynamic parameters of the employed metal hydrides. The devices allow cooling temperatures of about 3 degrees C and a COPc, (coefficient of performance for cooling) over 0.6 for the CTBR system and 0.5 for the MFTR system with the following input conditions: driving heat temperature 213 degrees C, lowest heat rejection temperature 40 degrees C and maximal cooling temperature 20 degrees C. The calculated specific cooling power is about 30 W/kg(hydride) for the CTBR system and 23 W/kg(hydride) for the MFTR system. (C) 1998 Elsevier Science Ltd.