Modélisation thermique du stockage d'hydrogéne par absorption dans un réservoir d'hydrures

Abstract

Magnesium hydride is the best candidate for the reversible hydrogen storage in atomic form. Indeed, thanks to its high specific storage capacity, abundance and lower prices compared with other metal hydrides, it will be used on a large scale at near future to allow a quick development of fuel cells. The laws that govern the chemical and thermal phenomena of the hydrogen storage have been determined experimentally. Numerical simulation, allows predicting and understanding the spatial and temporal evolution of the hydrogen storage reaction. In addition, the computational tool saves important time for the design and the optimization of hydrogen tanks. In this work, we describe a developed model of charging / discharging a specific magnesium hydride tank for better control of the phenomenon. Also, we particularly interested about the thermal description of the reactions generated by the process of hydrogen absorption and desorption. FLUENT software of ANSYS 13.0 was used to realize numerical simulations. One of its specific advantages consists of the important part that it attaches to the modeling of thermodynamics and kinetics of reactions between a gas and a porous medium (Metal Hydride). A subroutine written in C, called UDF for (User Defined Function) was developed by us and included in FLUENT. The results were validated by those available in the literature and have been the subject of many publications and international meetings. These results are the fruits of simulations on 2D and 3D geometries tanks initially heated to 300°C and at a storage pressure of 1 MPa. The equations that govern hydriding reaction are solved with a numerical scheme for fully implicit finite volume. The effect of different kinetic equations of absorption reaction was examined in order to determine which one would produce similar results compared to experimental ones. The profiles of temperature and concentration with space and time values were plotted. Finally, the contours describing the gradients of temperature depending time were performed with the CFD-POST software. The results show that the mechanism of reaction, based on the method of bidimensional volume contraction with a constant velocity interface provides the best results in the minimum of calculation time and becomes more appropriate for the 2D simulations.