LaNi5 Hydride Research Articles

Design and optimization of longitudinally finned embedded tube-type hydride reactor based on standardized responses using MO-desirability-based technique

The current research comprehensively investigates a longitudinal finned LaNi5 hydride-based hydrogen storage device. The design factors, namely the heat fin's thickness and height, are selected for optimization. The employed Central Composite design formulated eight cases when design factors varied between 2–5 mm fin heights and 1–2 mm thicknesses. The investigation emphasized the influence of the contact area between the copper fin and LaNi5 hydride on output responses such as 90 % and 100 % saturation time, thermal power, and alloy weight ratio. The optimal design for the longitudinally finned hydride reactor is determined using a quadratic regression model and a multi-response desirability technique. The desirability approach indicated a final design archetype for a capacity of 5 kg LaNi5 (assuming 20 % expansion volume) comprising a fin thickness of 1 mm and a height of 5 mm, yielding a combined desirability of 0.737. The simulation results of the optimum design show response values of 131 s, 612 s, 0.572, and 233.39 W/kg for 90 % saturation, 100 % saturation, weight ratio, and thermal power, respectively, against the regression model predicted values of 129.5 s, 609.33 s, 0.572085, and 233.587 W/kg with an overall deviation less than ±1.5 %. Additionally, a comparative study against the reactor designs reported in the literature revealed the modeled design's betterment, and henceforward, scaling up the present design improved the weight ratio without much hampering the absorption time and thermal power. Subsequently, a sensitivity study is performed to evaluate the means by which different operational conditions impact system performance.

Thermodynamic analysis of a metal hydride hydrogen compressor with aluminium substituted LaNi5 hydrides

The operating conditions of a Metal Hydride Hydrogen Compressor (MHHC) is often dictated by the hydride used to build it. This research focuses on finding the appropriate operating conditions for MHHC to get the ideal throughput and efficiency using aluminium based hydrides. For this, hydrogen absorption and desorption characteristics of LaNi5-xAlx (where x is 0, 0.2 and 0.4) hydrides were studied for estimating the suitability of these materials for developing hydrogen compressor. From the Pressure Concentration Isotherms (PCIs) and van't Hoff plot, an estimate of the reversible hydrogen weight percent attainable, equilibrium pressure and absorption and desorption temperature range were collected and the effect of aluminium concentration on these properties was studied. Further thermodynamic analysis was made by calculating the performance parameters like thermal efficiency, isentropic work required, theoretical heat supplied and pressure ratio by varying the operating conditions like supply pressure (3–5 bar), absorption temperatures (20–40 °C), and desorption temperature (80–140 °C). It is observed that the higher aluminium content in the hydride allows the hydrogen compressor to be operated at a lower supply pressure. Whereas lower aluminium content in hydrides give higher thermal efficiency and discharge pressure for a particular desorption temperature, while requiring a higher supply pressure to perform efficiently. The maximum thermal efficiency within the studied operating conditions was found to be 0.24 for LaNi5 at 3 bar supply pressure, 30 °C absorption and 140 °C desorption temperature with a pressure ratio of 8.97.

Hydrogen release from a metal hydride tank with phase change material jacket and coiled-tube heat exchanger

Hydrogen fuel cells are received increasingly wide attention in order to develop green ships and reduce greenhouse gas emissions in the field of waterway transportation. Metal hydrides (MHs) can be used to store hydrogen for green ships due to their high volumetric storage capacity and safety. Various measures should be considered in the design and manufacture process of the MH reactor to strengthen its performance of heat and mass transfer and obtain an acceptable hydrogen storage capacity. In this work, LaNi5 hydride is used as the hydrogen storage material and packed in the reactor. A basic axisymmetric numerical model for the hydrogen storage system without a heat exchanger has been developed and proved to be effective through the comparison between its simulation results and the published data during dehydriding. A hybrid heat exchanger, which is consisted of a phase change material (PCM) jacket and a coiled-tube, has been applied into the hydrogen storage system to relieve the thermal effect of MH in the dehydriding process on system performance. Effects of the heat transfer coefficient between the circulating heating water in the coil-tube and the MH bed, the temperature of circulating heating water and the pressure at the outlet on the dehydriding performance have been investigated. Based on parametric study, the relationships among the average dehydriding rate, the heat transfer coefficient, the heating water temperature and the outlet pressure have been found and fitted as simple equations. These fitted equations can be considered as a reference, which provides an important method to effectively control the dehydriding rate in order to satisfy the fuel requirement of the power unit and ensure the safe navigation of green ships in the future.

Predicting hydrogen adsorption and desorption rates in cylindrical metal hydride beds: Empirical correlations and machine learning

A major limitation in chemisorptive hydrogen storage in metal hydrides is the long time required for the adsorption reaction during charging. This study investigates how the shape and material of the reaction chamber influences the adsorption and desorption rates. Numerical simulations of hydrogen storage in a cylindrical reaction chamber filled with LaNi5 hydride are conducted for a range of chamber thermal conductivities and aspect ratios. The results show that adsorption and desorption processes are limited by thermal diffusion in the hydride bed and storage chamber. A storage efficiency is proposed based on an ideal isothermal process and used to evaluate the impact of chamber thermal conductivity and aspect ratio on the adsorption and desorption rates. Empirical correlations are proposed for predicting the adsorption and desorption efficiency of cylindrical LaNi5 hydride beds. Finally, a machine-learning based data model for predicting storage efficiency in metal hydride chambers is presented. Comparison against the empirical correlations highlights that the machine learning-based data model can predict the storage efficiency more accurately.

Selection of metal hydrides for a thermal energy storage device to support low-temperature concentrating solar power plants

Metal hydrides have become more and more significant both as hydrogen storage devices and as basic elements in energy conversion systems. Besides the well-known rare earth hydrides, magnesium alloys are very promising in the field of thermal energy storage for concentrating solar power plants. There is interest in analysing the performances of such materials in this context; for this purpose, a numerical model to describe hydrogen absorption and desorption processes of a metal hydride has been connected to a model elaborated with the help of Cycle-Tempo software to simulate a CSP plant operation. The integration of this plant with four metal hydride systems, based on the combination of two low-temperature hydrides (LaNi5, LaNi4.8Al0.2) and two high-temperature hydrides (Mg, Mg2Ni) has been studied. The investigation has taken into account CSP overall performances, transfer surfaces and storage efficiencies, to determine the feasibility of designed plants. Results show that the selection of the optimal hydrides must take into account hydride operation temperatures, reaction enthalpies, storage capacities and kinetic compatibility. In the light of the calculated parameters, a solar ORC plant using R134a as the working fluid is a valuable choice if matched to a storage system composed of LaNi5 and Mg2Ni hydrides.

Selection of phase change materials, metal foams and geometries for improving metal hydride performance

This paper reports the numerical investigation of the effect of different phase change materials (PCMs) on the metal hydride (MH) behaviour in a reactor bed during the absorption process. The feasibility of integrating metal foams (MFs) into the phase change materials to improve the hydrogen storage performance of the system was also evaluated. A two-dimensional model for a LaNi5 hydride reactor equipped with different phase change materials has been developed. The selection of five different PCMs having a high latent heat of fusion and a range of melting temperatures were investigated. In addition, the effect of the mass and volume of the different PCMs on the hydrogen performance of the MH reactor was studied. It was found that LiNO3·3H2O PCM shown better performance than the other PCMs, its loading time is faster, and its mass within the reactor is enough to absorb the total heat generated from the MH during hydrogenation. Three different metals foam with three different porosities were integrated into the most suitable PCM with the appropriate dimension of a cylindrical reactor that shows the optimum performance. The obtained results indicated that the integration of the metal foams into the PCM show better heat transfer performance than the case of MH-PCM without metal foams. Two different configurations cylindrical and spherical MH reactors were investigated. The obtained results indicated that the two configurations have very similar behaviours. So, both configurations are good for the hydriding process within an MH reactor.

Experimental study of a metal –hydrogen reactor's behavior under the action of an external magnetostatic field during absorption and desorption

The aim of this work is to experimentally study, the behavior of a metal-hydrogen reactor (MHR) subjected to the action of an external magnetostatic field, during hydrogen absorption and desorption by the LaNi5 hydride. The reactor was surrounded by a copper coil crossed by a continuous current delivered by a DC generator. In this study, the mass of the absorbed and desorbed hydrogen was measured and plotted for different initial temperatures and pressures functions of the applied magnetostatic field. The ratio of the hydrogen mass absorbed or desorbed with and without supplying a magnetostatic field was estimated after which the change in the saturation magnetization per 1 mol of desorbed hydrogen atom (ΔMs), for the LaNi5 compound; was determined.The results demonstrated that while the increase in temperature was not beneficial for the absorption reaction, it improved the desorption process. The increase in pressure leads to an increase in the absorbed hydrogen mass. The effect of the applied magnetostatic field was observed especially for the lowest temperatures in the case of the absorption reaction. In fact, we noticed a small increase in the absorbed mass, which decreased and disappeared in the highest temperatures. It was found that the magnetostatic field had no effect on the desorption reaction for the tested fields and temperatures. The low value of ΔMs confirmed the paramagnetic nature of the sample.

Experimental study of metal–hydrogen reactor behavior during desorption under heating by electromagnetic induction

The objective of this work is to study experimentally the behavior of a metal–hydrogen reactor (MHR) during hydrogen desorption by the LaNi5 hydride. The reactor is surrounded by a small coil traversed by an alternative sinusoidal current. The effect of the voltage applied to the coil is studied. Two kinds of tests are done. In the first one, the reactor is heated to the desired temperature and then it was put in contact with a tank at weak pressure (desorption), and in the second one, desorption and heating start simultaneously. Desorbed mass and temperature evolution within the hydride bed and in the reactor wall, as a function of time, are plotted. A comparison of results obtained by the electromagnetic induction heater and by heat exchanger provisioned by a hot fluid shows an improvement of the efficiency of the reactor when compared to the traditional hot system (fluid system).

LaNi5 hydride powder flowability as a function of activation and hydrogen content

Volume expansion of hydrogen absorbing materials, together with inter-particle friction can cause tension accumulation in hydride containers during absorption. When hydride particles absorb hydrogen there is an important volume increase, in the order of 25%. Particles have to accommodate to the container geometry but this movement is opposed by inter-particle friction. Under certain conditions tensions can build up, compromising the mechanical integrity of the container. This phenomenon needs to be addressed at the design stage to avoid mechanical failure of the container.Flow behavior of powder materials is a relevant technological field, usually addressed by means of qualitative or quantitative flowability measuring devices. The rotating drum technique, while mainly qualitative, is well established and can be modified into a completely sealed unit. To determine the flowability of a hydride under different activation stages and hydrogen content levels we developed a rotating drum device that can be pressurized with hydrogen or depressurized. We report particle size evolution and flowability measurements of a hydrogen absorbing material (LaNi5) at different stages of activation for both absorbed and desorbed states. The results of the present study show that the flowability of LaNi5 in more dependent on the degree of activation of the sample than on hydrogen absorption state.

High temperature metal hydrides for energy systems Part B: Comparison between high and low temperature metal hydride reservoirs

A dynamic analysis model aimed at describing the hydrogen absorption and desorption phases of a metal hydride has been calibrated for magnesium hydride in Part A of the present work. We can make use of the estimate of the main kinetic parameters associated to this kind of hydride in order to study the behaviour of a metal hydride-based energy system.A metal hydride becomes the basis of an energy system when the enthalpy related to its hydriding/dehydriding reactions is used by an applicator. Therefore, magnesium hydride, which is a high-temperature hydride, can be virtually placed in an energy system thanks to the model and its main energy-related characteristics can be calculated. This allows us to get a glimpse of the performances of magnesium hydride in the field of energy production and to compare them to those of well-established low-temperature hydrides, such as LaNi5 hydride.

Static and dynamic measurement-based thermodynamic analysis of solid sorption refrigeration system

Summary Pairs of low-temperature (La0.9Ce0.1Ni5 and La0.8Ce0.2Ni5) and high-temperature (LaNi4.7Al0.3 and LaNi4.6Al0.4) LaNi5 hydrides were used for thermodynamic analysis of metal hydride-based solid sorption refrigeration system (SSRS). In general, static pressure–concentration isotherm (PCI) properties were considered for the thermodynamic analysis of solid sorption thermodynamic cycles. But, the hydrogen transfer processes involved in the thermodynamic cycle are dynamic in nature. Therefore, in the present study, the dynamic PCIs of these metal hydrides were measured at different temperatures and compared with their static PCIs. Significant variation in PCI and thermodynamic properties were observed in dynamic conditions compared with static conditions. Later, the performance of SSRS was determined by using static and dynamic PCI properties. Refrigeration effect and coefficient of performance of SSRS decreased by 60% and 35% respectively, when dynamic (at 80 mi/min) PCI data were considered. Copyright © 2016 John Wiley & Sons, Ltd.

Accurate heat of formation for fully hydridedLaNi5 via the all-electron full-potential linearized augmented plane wave approach

The heat of formation, ΔHf, for La2Ni10H14, an important property for hydrogen storage, was remarkably overestimated in calculations, and has discouraged the use of first principles total energy methods in the search for novel metal hydrides. Here, we employ the all-electron full-potential linearized augmented plane wave method within both the generalized gradient approximation (GGA) and the local density approximation (LDA), along with a unique treatment of the total energy of the H2 molecule, which plays a critical role in ΔHf determinations. The calculated electronic properties indicate that charge transfer from the interstitial region to the H atoms stabilizes LaNi5 hydride. We find the calculated ΔHf (−31.3 kJ∕mol H2) within GGA is in excellent agreement with experiment (∼−32 kJ∕mol H2), as are the predicted geometrical structures for LaNi5 and La2Ni10H14. Surprisingly, although LDA calculations underestimate the volume of LaNi5 by 10.4%, the final value of ΔHf (−31.2 kJ∕mol H2), is also in excellent agreement with experiment.

Mathematical modelling of hydrogen storage in a LaNi5 hydride bed

This paper presents a numerical investigation of hydrogen storage in a metal hydrid bed. For this purpose, a two-dimensional mathematical model which considers complex heat and mass transfer and fluid flow during the hydriding process is accomplished in this study. The coupled differential equations are solved with numerical method based on integrations of governing equation over finite control volumes. The driving force for fluid flow is considered to be pressure difference due to the temperature distribution in the system. It is found that fluid flow enhances the local hydriding rate in the system by driving the hot fluid to the colder regions. The numerical results were found to agree satisfactorily with the experimental data available in the literature. Copyright © 2003 John Wiley & Sons, Ltd.

Defects Formation in LaNi5-based Alloys Investigated by In-situ X-ray Diffraction

ABSTRACTDefects formation in LaNi5-based alloys was investigated by X-ray diffraction (XRD). In-situ XRD data measured along the first hydriding-dehydriding P-C isotherms were analyzed by the Rietveld method. Lattice strain and crystallite size were evaluated from the peak profile. In LaNi5hydride phase formed accompanying with 2 % of anisotropic lattice strain in <hk0> direction caused by dense dislocations. Coexisting solid solution phase was not affected by the strain in the hydride phase. Lattice parameterabecame smaller after cycles than before hydriding, which is related with vacancies formation.Only 5 % of Al substitution for Ni dramatically changed the defects formation behavior. Hydride phase did not show lattice strain in the first hydriding but showed small strain during dehydriding. Formation of both dislocations and vacancies are strongly affected by substitution of other elements for a part of Ni.

Stabilisation of high dissociation pressure hydrides of formula La1−xCexNi5 (x=0–0.3) with carbon monoxide

We have previously demonstrated the efficiency of CO and SO2 surface treatments for the stabilization of the LaNi5 hydride. The as-treated hydrides were stable in air at room temperature. Here, CO surface treatment is applied to higher dissociation pressure systems, La1−xCexNi5 (x=0, 0.1, 0.2 and 0.3) compounds. Stabilization of the hydrides is studied at two temperatures, 273 and 298K. We found that the hydrogen retention time for CO-treated La1−xCexNi5 hydrides is dramatically improved compared with that of untreated hydrides. Nevertheless, for both temperatures, the hydrogen retention time in treated hydrides is found to decrease with increasing cerium content. The results are explained on the basis of P–C–T measurements carried out at room temperature. As expected, the hydrogen absorption and desorption pressures and the hysteresis increase with cerium content. The dehydrogenation kinetics of CO-treated hydrides is related to the cerium content of the alloys.

The hydrogen confinement in LaNi 5 and LaNi 5Zr 0.1 hydrides using poisonous gases

It has been shown that both CO and SO 2 gases have the effect of sealing the LaNi 5-hydride surface and therefore confining hydrogen. The sealed hydride is then stable in air at atmospheric pressure. We describe here the behaviour of CO treated LaNi 5 and LaNi 5Zr 0.1 hydride powders with average particle size and temperature dependence of the sealing effect. The effect of an additional SO 2 treatment to the CO-treated hydride is also demonstrated. The samples are studied by means of XRD, SEM, EPMA, XPS and PAC methods.

The Confinement of Hydrogen in LaNi5 Hydride Using Surface Poisoning

Abstract It has been found that an LaNi5 hydride treated with a CO gas is stable in air at room temperature. The hydrogenation of acetophenone or 1-octene was performed using the CO-treated hydride. The reaction well proceeded and it was confirmed that hydrogen confined in the hydride can be available for reactions. The use of the CO-treated LaNi5 hydride, therefore, can simplify the operation for hydrogenation.

Influence of the material and the shape of the container on LaNi5 hydride formation

Intermetallic compounds, and particularly LaNi5, absorb large amounts of hydrogen under moderate conditions of temperature and pressure. The LaNis formation is accompanied by an important energy production. As shown previously [1], during the reaction the effective sample temperature is different from the imposed temperature of the furnace. This difference is about 20 K when 300 mg LaNi 5 is hydrided and is always < 2 K for a sample mass smaller than 30 mg. In this letter experimental results are reported with the aim of clarifying the role of sample temperature changes on hydriding kinetics. First, the studies were carried out using sample holders characterized by very different thermal conductivities. Secondly, with the aim of modifying the quantity of heat produced, some experiments were done by increasing the sample mass from 70 to 300 mg. In conclusion, the influence of these heat-transfer modifications on the shape of the experimental curves is analysed. Mass measurements are carried out using a high-pressure microbatance with a limiting accuracy of 1 ~g. In order to determine the sample temperature changes throughout the experiment, two chromel-alumel thermocouples were used, one in the LaNi 5 bed and the other in an inert powder. The temperature gradient was evaluated as the temperature differed between the two samples. The sample holder was a cylindrical flat-bottomed cup 0.5 mm thick and 5 mm deep with a diameter of 10 mm. Other holders had the special design shown in Fig. lb, which mainly consisted of a large lateral surface which ensured the maximum heat exchange with the surrounding gas phase. These holders were machined from materials such as stainless steel, copper or plexiglass. The LaNi5 compounds, prepared by induction melting of the pure components in vacuum, were activated by performing about 20 absorption

An investigation of the intrinsic degradation mechanism of LaNi 5 by thermal desorption technique

The intrinsic degradation behavior of LaNi 5 was investigated by the changes of pressure-composition-temperature ( P-C-T) curves of LaNi 5H 2 system and the hydrogen desorption technique after the pressure induced hydrogen absorption-desorption cycling. Thermal desorption experiment of LaNi 5 hydrides showed only one peak in the hydrogen evolution rate vs temperature plot for the activated samples but two peaks for the degraded samples. The low temperature peak of the degraded samples and a peak of the activated sample related to the hydrogen evolved from the sites which hydrogen could absorb into and desorb from reversibly. reversibly. The high temperature peak of the degraded samples seems to be associated with the hydrogen from the stable hydrides such as several series of LaNi stoichiometric compound hydrides and LaH 2. Such stoichiometric compound hydrides and LaH 2 would be formed by the disordering of the lattice and the changes of local composition of the degraded LaNi5 hydrides. Ni clusters formed at the surface by the cycling were confirmed by the magnetization measurement, which indicates the formation of a series of stable hydrides. Thus it is concluded that the formation of the various stoichiometric compound hydrides and LaH 2 were responsible for the intrinsic degradation of LaNi 5 through the cycle.

Magnetic properties of LaNi5and their variation with hydrogen absorption and desorption

The hydrogen storage compound LaNi5 is an exchange-enhanced Pauli paramagnet with susceptibility chi (LaNi5)=4.6*10-6 EMU g-1. Hydrogen absorption leads to a decrease of the susceptibility of chi (LaNi5H6.0)=1.3*10-6 EMU g-1. This decrease is usually covered by a strong irreversible increase of surface magnetism, where, through surface segregation and decomposition, superparamagnetic Ni precipitations are formed. The two effects explain the controversial results about the magnetic properties of the LaNi5 hydride. The implication of this decomposition on the cyclic lifetime is discussed.