Faouzi Askri

Study of two-dimensional and dynamic heat and mass transfer in a metal–hydrogen reactor

Abstract To analyse heat and mass transfer in a metal–hydrogen reactor, the hypothesis that disregards the radiative heat transfer in the reactor, is typically used. In this paper, we take into account the radiative heat transfer and we test the validity of this hypothesis in the case of the LaNi 5 and in the case of the magnesium. A theoretical model is conducted for the two-dimensional system where conduction, convection radiation and chemical reaction take place simultaneously. This model is solved by the finite volume method. The numerical simulation is used to present the time–space evolutions of the temperature and the hydride density in the reactor and to determinate the sensitivity to some parameters (absorption coefficient, scattering coefficient, reactor wall emissivity).

Prediction of transient heat and mass transfer in a closed metal–hydrogen reactor

Abstract The metal–hydrogen reactor is usually composed of a porous medium (hydride bed) and an expansion volume (gaseous phase). During the sorption process, the hydrogen flow and the heat transfer in the expansion part are badly known and can have some effects on the sorption phenomena in the hydride medium. At our knowledge, the hypothesis that neglects those effects is typically used. In this paper, a 2D study of heat and mass transfer has been carried out to investigate the transient transport processes of hydrogen in the two domains of a closed cylindrical reactor. A theoretical model is conducted and solved numerically by the control-volume-based finite element method (CVFEM). The result on temperature and hydride density distribution are presented and discussed. Moreover, this paper discusses in detail the effects of some governing operating conditions, such as dimensions of the expansion volume, height to the radius reactor ratio, and the initial hydrogen to metal atomic ratio, on the evolution of the pressure, fluid flow, temperature and the hydrogen mass desorbed.

Dynamic behavior of metal–hydrogen reactor during hydriding process

Abstract The present study involves numerical simulation of transient transport of hydrogen and heat within a metal–hydrogen reactor connected to a hydrogen tank during the hydriding process. This problem is of particular interest in the design of many installations in the field of energy technology (compressor, heat pumps, thermal or hydrogen storage systems). The reactor presents an expansion volume for hydrogen. The hydrogen flow is described by general momentum conservation equations instead of Darcys law. The evolutions of the temperature, of the hydrogen concentration and of the hydrogen flow velocity are presented. The effects of the reactor dimensions, the inlet diameter, the volume of the expansion part, the tank volume, the initial pressure and the amount of hydrogen in the tank, on the heat and hydrogen transfer are determined.

Unstructured Control-Volume Finite-Element Method for Radiative Heat Transfer in a Complex 2-D Geometry

Abstract This article describes a new approach based on the control-volume finite-element method (CVFEM) for computing radiative heat transfer in a complex two-dimensional geometry using a general unstructured grid. To examine its accuracy and computational efficiency, five test cases are investigated, and the results obtained agree very well with other published works. In addition, the study presented in this article shows that not only this method is flexible in treating radiative heat transfer in complex geometry, but also that the computer procedure based on this numerical method needs an accurate computer process unit (CPU) time and can be combined easily with developed codes for fluid dynamics.

Analysis of two-dimensional transient conduction–radiation problems in an anisotropically scattering participating enclosure using the lattice Boltzmann method and the control volume finite element method

Abstract This study deals with the performance evaluation of the lattice Boltzmann method (LBM) and the control volume finite element method (CVFEM) in terms of their abilities to provide accurate results in solving combined transient conduction and radiation mode problems in a two-dimensional rectangular enclosure containing an absorbing, emitting and anisotropically scattering medium. Coupling problems for mixed kind thermal boundary are worked out for reflective interfaces. Effects of various parameters are studied on the distributions of temperature, radiative and conductive heat fluxes. The results of the LBM in conjunction with the CVFEM have been found to compare very well with available results in the literature. So, the numerical approach is extended to deal with a practical combination of mixed boundary conditions in a transient multi-dimensional combined conductive radiative heat transfer problems in an emitting, absorbing, anisotropically scattering enclosure.

Effect of Thermal Conductivity of the Phase Change Material (PCM) on the Absorption Process of a Metal-Hydrogen Reactor (LaNi5-H2)

In order to make the storage mode in a metal-hydrogen reactor (LaNi5-H2) more cost competitive in terms of thermal energy, we propose in this study to store the released heat during hydrogen absorption (exothermic) by using a phase change material (PCM), for recovering it during desorption process. A transient two-dimensional mathematical model to predict the heat and mass transfer in the hydride bed and the phase change medium is presented and solved numerically by the unstructured control volume finite element method (CVFEM). For this model, the liquid fraction in the PCM was described by an analytic approximation of the Heaviside step function which, to the knowledge of the authors, is applied for the first time to study phase change problems. The validation of the numerical model has been performed by comparison with experimental data, and several numerical simulations were carried out to evaluate the effect of the thermal conductivity of PCM on the dynamic behavior of hydriding and the melting processes.