MODELING 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. Th e model considers the effects of heat transfer by conduction in the me tal hydride reaction beds, conduction-convection in the heat transfer fluid, hydrogen flow governed by Darcy's law and gas consumption by so rption kinetics. The model was applied to simulate two different conce pts of fast reaction beds in the heating/air-conditioning device, usin g a novel capillary tube bundle reactor (CTBR) for improved heat trans fer characteristics and the established metal foam tube reactor (MFTR) , respectively. The reactors are equipped with cascades of different m etal hydrides thus implying a moving thermal wave during operation. Nu merical 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 param eters of the employed metal hydrides. The devices allow cooling temper atures of about 3 degrees C and a COPc, (coefficient of performance fo r cooling) over 0.6 for the CTBR system and 0.5 for the MFTR system wi th the following input conditions: driving heat temperature 213 degree s C, lowest heat rejection temperature 40 degrees C and maximal coolin g temperature 20 degrees C. The calculated specific cooling power is a bout 30 W/kg(hydride) for the CTBR system and 23 W/kg(hydride) for the MFTR system. (C) 1998 Elsevier Science Ltd.