MODELLING OF THERMO-FLUIDODYNAMIC PHENOMENA IN METAL HYDRIDE-VESSELS

The numerical approaching method (1) becomes a necessary instrument to understand the hydrogen reaction and heat transfer mechanism in a reactor in order to design more efficient heat exchanger (2). A two-dimensional thermofluidodynamic analysis of heat and mass transfer in a metal- hydrogen reactor is described in this paper. The experimental apparatus simulated consists of a metallic container with stainless steels walls, filled with a metallic powder of LaNi 5 . At t = 0, the powder is free of hydrogen and is set at an initial temperature. A source of hydrogen is connected via a valve to the reactor and it is set at a constant pressure. When the valve is opened the gas enters the reactor and flows through the porous metallic powder. At this point the absorption process starts and owing to its exothermic character a temperature increase in the reactor occurs. The model developed in this paper supposes that the gas pressure is constant in the reactor and that solid and gaseous phases are in thermal equilibrium. The gas phase is assumed ideal from the thermodynamic point of view. The hydrogen flow is described by means of Darcy's law for porous media where the pressure gradient is the only driving force. Heat equation, momentum equation and continuity equation are numerically solved with the finite element technique by using the COMSOL Multiphysics software. Using thermophysical parameters like density, dynamic viscosity, thermal conductivity thermal, enthalpy of absorption calculated with thermodynamic databases the reaction kinetic of absorption/desorption can be simulated such as the time-space evolution of the temperature. References