Modeling of heat and mass transfer in LaNi5 matrix during hydrogen absorption-desorption cycle

Olaitan L Akanji,Andrei V Kolesnikov

doi:10.2478/v10026-012-0087-0

Olaitan L Akanji, Andrei V Kolesnikov

Open Access

https://doi.org/10.2478/v10026-012-0087-0

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Abstract

Packed bed reactors using metal hydride are attracting a lot of attention as potential hydrogen storage systems. Some operational and design variables are major constraints to obtain a proper infl ow/outfl ow of hydrogen into a metal hydride reactor. These variables include packed bed thermal conductivity, porosity, pressure and temperature distributions in the reactor during the absorption/desorption cycle. They also cause a mechanical stress induced by temperature gradient. In this paper, two dimensional models are implemented in COMSOL multiphysics to simulate the hydrogen fl ow, pressure and temperature distributions in the packed bed reactor during absorption/desorption cycle. Also, stresses in porous metal hydride induced by temperature variation in the heating/cooling cycle were evaluated. A possible effect of stress induced, porosity changes on diffusion and heating of hydrogen in both radial and axial direction in packed bed is discussed. The model consists of a system of partial differential equations (PDE) describing structural mechanics of stress, heat and mass transfer of hydrogen in the porous matrix of the packed bed reactor.

Highlights

Due to the high demand and a consistent usage of non-renewable carbonaceous fuels worldwide such as gasoline, there is a need to provide an alternative energy source that will serve the same purpose as gasoline[1].Hydrogen has been receiving great boost throughout the world as an alternative energy to be used in a fuel cell
Efficient release of hydrogen gas in the metal hydride reactor should meet the need of fast load variation in order to build and satisfy such hydrogen systems, physics of the transport process coupled with reaction kinetics are very important such as hydrogen mass flow in the hydride bed, heat transfer within the bed and local hydrogen absorption rate
Absorption / Desorption process was simulated for hydrogen storage tank filled with metal hydride

Summary

INTRODUCTION

Due to the high demand and a consistent usage of non-renewable carbonaceous fuels worldwide such as gasoline, there is a need to provide an alternative energy source that will serve the same purpose as gasoline[1]. Jemni and Nasrallah[2] presented a model for the two-dimensional transient heat and mass transfer within a cylindrical reactor. Nakawaga et al.[5] predicted the transient heat and mass transfer phenomenon through the hydride bed by using a two-dimensional mathematical model with hydriding and dehydriding kinetics. Suda et al.[6] compared their mathematical model with the experimental data obtained from a cylindrical vessel In their experiments, the hydrogen bed was cooled or heated by water flowing in an annular shell around the vessel; as a result, their model was only compared with experimental results for validation as one- dimensional model. A 2-dimensional reactor configuration has been simulated consisting of two rectangular enveloped with fins where there is discharge/charge of hydrogen in metal hydride. Mass balances for hydrogen diffusion and momentum balances which includes Darcy’s term to account for momentum transfer due to pressure gradient in the metal hydride porous media

MODELING EQUATIONS The following equations are incorporated in COMSOL

RESULTS AND DISCUSSION

CONCLUSIONS

LITERATURE CITED