Modeling of Hydrogen Absorption/Desorption in a Metal Hydride Bed Reactor — A Theoretical Study
Hydrogen has been considered as an alternative source of fuel to the fossil fuel in future, most especially, for mobile applications. However, a requirement is the safe, efficient and compact onboard storage of hydrogen. Reversible storage in metal hydride is promising, but adequate knowledge of materials system fulfills all requirements regarding hydrogen content is a major drawback, release temperature, and reversibility simultaneously. Hydrogen absorptiondesorption in a metal hydride bed reactor can be modeled using different software such as FLUENT, CFDACE, and COMSOL Multiphysics. This book chapter will focus on the use of software COMSOL Multiphysics to simulate the diffusion and heating of hydrogen and metal hydride powder in both radial and axial directions. The model consists of system of partial differential equations (PDE) describing two-dimensional heat and mass transfer of hydrogen in a porous matrix. The influence of the operating parameters Temperature, Pressure, Concentration, Permeability and Thermal Conductivity on the rate of absorption-desorption of hydrogen in metal hydride will be fully discussed. The simulation results obtained could be applied to the on board hydrogen storage technology, in particular for the hydrogen supply of a fuel cell for powering of a hydrogen fuel cell vehicle.
Thermal–fluid behavior of the hydriding and dehydriding processes in a metal hydride hydrogen storage canister
A study of the hydrogen absorption and desorption processes using LaNi5 metal hydride is presented for investigation on the influences of expansion volume and heat convection. The hydrogen storage canister comprises a cylindrical metal bed and a void of expansion volume atop the metal. The expansion volume is considered as a domain of pure hydrogen gas. The gas motion in the metal hydride bed is treated as porous medium flow. Concepts of mass and energy conservation are incorporated in the model to depict the thermally coupled hydrogen absorption and desorption reactions. Simulation results show the expansion volume reduces the reaction rates by increasing thermal resistance to the heat transfer from the outside cooling/heating bath. The assumption usually adopted in simulating heat transfer in a metal hydride tank that heat convection in the reaction bed may be ignored is not valid when expansion volume is used because heat convection dominates the heat transfer through the expansion volume as well as the metal bed. The details of the thermal flow pattern are demonstrated. It is found that, due to the action of thermal buoyancy, circulations are likely to happen in the expansion volume. The hydrogen gas accordingly, instead of going directly between the inlet/outlet and the metal bed, tends to move with the circulation along the boundary of the expansion volume.
Great American Bridges and Dams
Bridges: Spanning the Nation. Dams: Controlling a Precious Resource. Saving Bridges and Dams. Guide to the Guide. THE BRIDGES AND DAMS. New England. Mid-Atlantic. South. Midwest. Southwest. West. Epilogue: The Ones That Got Away. Further Reading. Information Sources. Index.