Modeling and simulation of a large-scale metal-hydride storage tank on the basis of sodium alanate

Abstract

Paper presented at the 7th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Turkey, 19-21 July, 2010.

In the framework of the European Union project STORHY (Hydrogen Storage for Automotive Applications) a metal­-hydride storage tank with 8 kg sodium alanate has been recently built. A main challenge is the heat management of the system caused by the high energy flows during the exothermic loading of the hydride storage tank in relatively short periods. For the prediction of operation in passenger cars a model for the thermal behavior of this storage tank has been developed which takes into account the thermodynamic properties of the sodium alanate material as well as the reaction kinetics. These data have been derived by experiments and inserted into the balance equations. For different operating conditions an analysis has been performed. This refers to three different flow rates of the heat transfer fluid (trade name Marlotherm X). At the beginning the storage tank does not contain any hydrogen. The initial temperature of the system is 100 °C and the absorption pressure 100 bar. The inlet temperature of the heat transfer fluid has been set to 100 °C. The heat transfer coefficient between the storage elements and the heat transfer fluid depends on its flow rate. The transient absorption behavior of the storage tank has been calculated . Furthermore, it has been investigated to which extent the loading behavior can be accelerated by enhanced heat transfer due to insertion of flow baffles on the side of the heat transfer fluid.By simulation the potential for optimization of the tank geometry and the flow conditions for loading and deloading can be determined.