Hydrogen Absorption Time Research Articles

Enhancement of heat transfer in hydrogen storage tank with hydrogen absorbing alloy (optimum fin layout)

AbstractOptimization of the fin layout in a metal hydride (MH) bed has been sought to enhance poor heat transmission in a hydrogen storage tank, and to obtain a maximum hydrogen absorption rate with a smaller volume of fins. Two different fin configurations, radial and circular fins, in a vertical cylindrical reactor vessel were tested with a La‐Ni‐based AB5 type hydrogen storage alloy. A two‐dimensional transient heat conduction analysis, coupled with predicted temperature and concentration of absorbed hydrogen in the bed for the exothermic hydride reaction, was used to evaluate enhancement of the hydrogen absorption time. The estimated temperature and concentration agreed within 6 K and 8.5%, respectively, with our experimental results. The effect of thickness and the spacing and shape of fins on the hydrogen absorption time were analytically evaluated, so that the optimum range of the each fin layout was obtained by the trade off between absorption time and reduction in the MH volume due to the volume occupied by fins. The hydrogen absorption time for the recommended layout of circular fins was reduced to approximately one‐third of that without fins. © 2008 Wiley Periodicals, Inc. Heat Trans Asian Res, 37(3): 165–183, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/htj.20195

Cyclic hydrogen storage properties of Mg milled with nickel nano-powders and MnO 2

The cyclic hydrogen storage properties of nanocrystalline composite of Mg–3Ni–2MnO 2 (wt.%) produced by mechanical milling with nickel nano-powders under hydrogen pressure and its structural changes have been investigated. The results show that the composite has excellent hydrogen storage properties. Its maximum hydrogen capacity is about 6.5 wt.%. The hydrogen absorption time is ∼50 s in which 6.37 wt.% of hydrogen has been absorbed at 200 °C. The hydrogen desorption time is ∼310 s in which the same amount of hydrogen has been discharged in the temperature range from 285 to 310 °C under hydrogen pressure of 0.1 MPa. The composite also has a better cyclic hydrogen storage property. After 60 times of cycling, the hydrogen capacity decreases less than 0.1 wt.%. However, the hydrogen absorption time and desorption time are increased with the cyclic numbers. The reasons for these may be that the MgO, formed during the cycling process, impedes contact of the catalyst with the MgH 2.

Cyclic hydrogen storage properties of Mg milled with nickel nano-powders and NiO

Abstract The cyclic hydrogen storage properties of nanocrystalline composite of Mg–3Ni–2NiO (wt.%) produced by mechanical milling with nickel nano-powders under the hydrogen pressure have been investigated. The results show that the composite has excellent hydrogen storage properties. Its maximum hydrogen capacity is about 6.4 wt.%. The hydrogen absorption time is about 54 s in which 6.1 wt.% of hydrogen has been absorbed at 200 °C. The hydrogen desorption time is about 310 s in which 6.2 wt.% of hydrogen has been discharged in the temperature range from 290 °C to 320 °C under the hydrogen pressure of 0.1 MPa. The composite also has a better cyclic hydrogen storage behavior. The hydrogen capacity is decreased less than 0.1 wt.% after 60 times of cycling. However, the hydrogen absorption time and desorption time are increased in proportion with the cyclic numbers. The reason for these may be that the MgO, formed during the cycling process, impedes an intimate contact of the catalyst with the MgH 2 .

Hydrogen absorption/desorption kinetics of magnesium nano-nickel composites synthesized by dry particle coating technique

Dry particle coating technique was utilized for coating nano-nickel on magnesium particles. The objectives of this study were to evaluate the effects of the nanocatalyst (Ni) on the hydrogen absorption and desorption kinetics of the Mg-based composite (Mg–Ni). Hydrogen absorption curves plotted as a function of time showed that composites processed for longer periods of time exhibited significantly higher hydrogen absorption rates. With increased coating time, the catalyst was more evenly distributed over the Mg surface, resulting in the formation of a composite with increased hydrogen capacity and kinetics. Meanwhile, no significant morphology change in the composites was observed. A change in the hydrogen absorption rate as a function of time was observed. This change in rate implies a change in the rate limiting mechanism from chemical absorption on the Mg particle to diffusion into the Mg particle. TGA results showed that lower coating speeds resulted in lower initial desorption temperatures as well as steeper desorption rates. Higher heating rates resulted in faster reaction rates and therefore reduced hydrogen absorption time and increased hydrogen storage capacity.

5016 ハイブリッド型水素貯蔵容器の水素充填特性(S53 水素貯蔵技術における熱工学的諸問題,S53 水素貯蔵技術における熱工学的諸問題)

Hybrid hydrogen storage tank is a high pressure hydrogen tank combined with metal hydrogen absorbing material to increase hydrogen mass stored per tank volume. It becomes an essential technology to supply hydrogen gas to fuel cell vehicles. However, poor heat transmission in MH bed during exoergic hydride forming reaction causes a long hydrogen charging time. This study shows basic characteristics of hydrogen charging rate and MH temperatures during hydrogen charging of a hybrid tank. Radial fin arrangement in cylindrical MH cartridge hydrogen charging enhances heat transfer in MH and reduces considerably hydrogen absorption time. The optimum fin number is also given by 2D numerical analysis.

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