Heat and mass transfer in metal hydride reaction beds: Experimental and theoretical results

Abstract2 LiNH 2 -1.1 MgH 2 -0.1 LiBH 4 -3 wt.% ZrCoH 3 is a promising solid state hydrogen storage material with a hydrogen storage capacity of up to 5.3 wt.%. As the material shows sufficiently fast desorption rates at temperatures below 200 °C, it is used for a prototype solid state hydrogen storage tank that is coupled to a HT-PEM fuel cell. In order to perform design simulations for this prototype reactor with a hydrogen capacity of 2kWh el , model equations for the rate of hydrogen sorption reactions are required.Therefore, several material properties, like bulk density and thermodynamic data, have been measured and they are summarized in the present publication. Furthermore, isothermal absorption and desorption experiments are performed in a temperature and pressure range that is in the focus of the coupling procedure. Using this experimental data, two-step model equations have been fitted for the absorption and desorption reaction. These empirical model equations are able to capture the experimentally measured reaction rates and can be used for model validation of the design simulations. KeywordsLi-Mg-N-H hydride, reaction rate, model equations, hydrogen storage IntroductionDue to high theoretical storage densities, complex hydrides show the potential to improve the present state of the art of hydrogen storage for automotive applications [1]. As the hydrogen is strongly bonded to the powdered material, the amount of free gaseous hydrogen in equilibrium at room temperature and pressure is small. Therefore, hydrogen is just released when external heat is provided for the endothermal desorption reactions. In case the storage reactor is coupled to a fuel cell (FC), the required amount of hydrogen can be released by transfer of the waste heat from the FC. This kind of coupled system has already been studied by several simulations and experiments for conventional metal hydrides as well as NaAlH 4 [2,3].The present work has been developed within a framework of activities aiming to realize a hydrogen storage tank that is studied in technically relevant scale, i.e. allowing for 2 h coupled operation with a 1 kW el high temperature proton-exchange membrane (HT-PEM) fuel cell. As for an appropriate tank design modelling and simulation tools are used, reliable information on the properties of the selected

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“…For this term, two basic mechanisms which are common for metal hydrides according to [24,25] or [26,27] …”

Section: Reaction Ratesmentioning

confidence: 99%

Material properties and empirical rate equations for hydrogen sorption reactions in 2 LiNH2–1.1 MgH2–0.1 LiBH4–3 wt.% ZrCoH3

Bürger

Vitillo

et al. 2014

International Journal of Hydrogen Energy

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“…The physics of this dynamic model follows the work of Mayer et al [1]. The model described in this paper is based on a bulk and geometrically resolved first principles approach that solves the dynamic conservation of mass and conservation of energy equations together with appropriate calculations for heat transfer and chemical reactions, drawing on the substantial metal hydride modeling work in the literature.…”

Section: Background and Motivationmentioning

confidence: 99%

“…Integration of hydrogen storage models into larger system models is becoming more important as metal hydride applications become more widespread [11]. Additionally, the experimental work reported in the literature generally centers on purpose built, ideal, experimental hydride reaction beds cooled by integrated cooling systems [1,7,8]. The experimental work reported in this paper employs an actual, commercially available, seasoned tank exposed to two general cooling environments.…”

Section: Background and Motivationmentioning

confidence: 99%

“…Closely following the work of Mayer et al [1] a hydride tank model was created to determine the tank temperature, the quantity of energy released, and the mass of hydrogen absorbed within each node of a discretized model when given local operating conditions such as temperature, heat transfer rates, and hydrogen inlet pressure. This was accomplished by simultaneously solving the conservation of mass and conservation of energy equations for the gaseous hydrogen and the solid metal alloy in each of the discrete nodes of the model.…”

Section: Model Descriptionmentioning

confidence: 99%

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Accurate simplified dynamic model of a metal hydride tank

Brown

Brouwer

Samuelsen

et al. 2008

International Journal of Hydrogen Energy

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“…Many researchers simulate highly transient performance of adsorption /desorption beds by using a constant heat transfer coefficients [7][8][9][10][11]. Mayer et al [12], Bjurström et al [13], Tsotsas and Martin [14], Murashov and White [15], and recently Yan et al [16] characterize the adsorption heat transfer by focusing on the thermal conductivity of the adsorbents. However, Freni et al [17] pointed out that the thermal conductivities of the CaCl 2 /SiO 2 and LiBr/SiO 2 composite sorbents was considerably affected by the amount water adsorbed.…”

Section: Introductionmentioning

confidence: 99%

A heat transfer correlation for transient vapor uptake of powdered adsorbent embedded onto the fins of heat exchangers

Thu

Ismail

et al. 2016

Applied Thermal Engineering

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Highlights Detailed study on transient heat transfer of an adsorbent coated heat exchanger. Adsorbent-adsorbate interaction contributes 75% of the total thermal resistance. Transient local heat transfer deviates from the overall value due to thermal mass. A correlation for the transient local adsorption heat transfer coefficient. ABSTRACTWe present a detailed study on the transient heat transfer phenomena of powdered-adsorbent mixed with an organic binder for adherence to the fins of a heat exchangers. The transient performance of such an adsorbent-heat exchanger configuration has significant application potential in the adsorption desalination plants and chillers but seldom addressed in the literature. An experiment is designed to measure the heat transfer for several adsorption temperatures under a single vapor component environment. Analysis on the experimental data indicates that the adsorbent-adsorbate interactions contribute about 75% of the total thermal resistances throughout the uptake processes. It is found that the initial local adsorption heat transfer coefficients are significantly higher than the average values due primarily to the thermal mass effect of the adsorbent-adsorbate interaction layers. From these experiments, a correlation for the transient local adsorption heat transfer coefficients is presented at the sub-atmospheric pressures and assorted application temperatures. KEYWORDS

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Heat and mass transfer in metal hydride reaction beds: Experimental and theoretical results

Cited by 212 publications

References 4 publications

Material properties and empirical rate equations for hydrogen sorption reactions in 2 LiNH2–1.1 MgH2–0.1 LiBH4–3 wt.% ZrCoH3

Material properties and empirical rate equations for hydrogen sorption reactions in 2 LiNH2–1.1 MgH2–0.1 LiBH4–3 wt.% ZrCoH3

Accurate simplified dynamic model of a metal hydride tank

A heat transfer correlation for transient vapor uptake of powdered adsorbent embedded onto the fins of heat exchangers

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