Metal Hydride Hydrogen Storage System Research Articles

Experimental investigation and theoretical modeling of dehydriding process in high-pressure metal hydride hydrogen storage systems

This study explores the endothermic dehydriding (desorption) reaction that takes place in a high-pressure metal hydride (HPMH) hydrogen storage system when hydrogen gas is released to the fuel cell. The reaction is sustained by circulating warm fluid through a heat exchanger embedded in the HPMH powder. A systematic approach to modeling the dehydriding process is presented, which is validated against experimental data using two drastically different heat exchangers, one using a modular tube-fin design and the other a simpler coiled-tube design. Experiments were performed inside a 101.6-mm (4-in) diameter pressure vessel to investigate the influences of hydrogen release rate, heat exchanger fluid flow rate and fluid temperature on the dehydriding process for the HPMH Ti1.1CrMn. It is shown the dehydriding reaction rate can be accelerated by increasing the fluid temperature and/or the rate of pressure drop. HPMH particles located in warmer locations close to heat exchanger surfaces both began and finished dehydriding earlier than particles farther away. 2-D and 3-D models were created in Fluent to assess the dehydriding performances of the modular tube-fin heat exchanger and coiled-tube heat exchanger, respectively. The models are shown to be quite accurate at predicting the spatial and temporal variations of metal hydride temperature during the dehydriding reaction.

Coiled-tube heat exchanger for high-pressure metal hydride hydrogen storage systems – Part 2. Computational model

This second part of a two-part study presents a transient, three-dimensional numerical model for a high-pressure metal hydride (HPMH) hydrogen storage system that is cooled by a coiled-tube heat exchanger. The model uses the same geometry examined in the first part of the study and its predictions are compared to experimental results also discussed in the first part. The model involves solving coupled heat diffusion and hydriding reaction equations for Ti 1.1CrMn. These equations are solved to determine the spatial distribution of hydride temperature as a function of time over the entire duration of the hydriding reaction, which is shown to agree favorably with the experimental data. The model also serves as an effective means for tracking the detailed temporal variations of the heat exchanger’s key performance parameters for different hydride locations relative to the coolant tube. These variations can aid in determining optimum placement of the coolant tube relative the hydride powder. Like the experimental study, the model proves that coolant temperature has the greatest influence on the time needed to complete the hydriding reaction.

Coiled-tube heat exchanger for High-Pressure Metal Hydride hydrogen storage systems – Part 1. Experimental study

This two-part study explores the development and thermal performance of a coiled-tube heat exchanger for hydrogen fuel cell storage systems utilizing High-Pressure Metal Hydride (HPMH). The primary purpose of this heat exchanger is to tackle the large amounts of heat released from the exothermic hydriding reaction that occurs when the hydrogen is charged into the storage vessel and is absorbed by the HPMH. The performance of heat exchanger was tested using 4 kg of Ti 1.1CrMn at pressures up to 280 bar. Tests were performed to assess the influence of different operating conditions on the effectiveness of the heat exchanger at removing the heat in a practical fill time (time required to complete 90% of the hydriding reaction). It is shown that distance of metal hydride particles from the coolant tube has the most dominant influence on hydriding rate, with particles closer to the tube completing their hydriding reaction sooner. Faster fill times were achieved by reducing coolant temperature and to a lesser extent by increasing pressurization rate. By comparing tests with and without coolant flow, it is shown that the heat exchanger reduces fill time by 75% while occupying only 7% of the storage pressure vessel volume. The second part of this study will present a 3D computational heat transfer model of the storage vessel and heat exchanger, and compare the model predictions to the experimental data.

Development of a hydrogen catalytic heater for heating metal hydride hydrogen storage systems

This paper describes the design, fabrication and performance evaluation of a high efficiency, compact heater that uses the catalytic oxidation of hydrogen to provide heat to a hydrogen storage system. The heater was designed to transfer up to 30 kW of heat from the catalytic reaction to the hydrogen storage system via a recirculating heat transfer fluid. The catalytic heater consists of three main parts: 1) the reactor, 2) the gas heat recuperator, and 3) oil and gas flow distribution manifolds. The reactor and recuperator are integrated, compact, finned-plate heat exchangers to maximize heat transfer efficiency and minimize mass and volume. Detailed, three-dimensional, multi-physics computational models were used to design and optimize the system. At full power the heater was able to catalytically combust a 10% hydrogen/air mixture flowing at over 80 cubic feet per minute and transfer 30 kW of heat to a 30 gallon per minute flow of oil over a temperature range from 100 °C to 220 °C. The total efficiency of the catalytic heater, defined as the heat transferred to the oil divided by the inlet hydrogen chemical energy, was determined to exceed the design goal of 80% for oil temperatures from 60 °C to 165 °C.

Reversible hydrogen-storage at reduced temperatures in the intermetallic compound Mg6(Ni,Pd)

A rapidly-solidified Mg–Ni–Pd alloy is shown to exhibit reversible hydrogen-storage of 5 mass % H at a temperature of 473 K, nearly 100 K below temperatures typically required for Mg-based alloys, with an equilibrium absorption plateau near 1 atm H2 pressure. Additionally, a single plateau is observed in the pressure–composition isotherm where MgH2 and Mg2NiH4 form and decompose simultaneously during the absorption/desorption process. The increase in absorption plateau pressure to 100 kPa suggests a decrease in the free energy by as much as 15 kJ/mol resulting from either a decrease in enthalpy or an increase in entropy of reaction between the hydride and metallic phases. The improved thermodynamics are discussed in terms of the formation of a new equilibrium metallic phase, Mg6(Ni,Pd). The phase alters the thermodynamics of the hydriding reaction, allowing both MgH2 and Mg2NiH4 to form cooperatively in a single reaction. This method for reducing the free energy of the hydriding reaction is promising, and may prove useful in a variety of other metal-hydride hydrogen-storage systems.

Charging dynamics of metal hydride hydrogen storage bed for small wind hybrid systems

Small hybrid wind systems are capable of storing and supplying power for residential applications. In this paper, the excess wind energy is converted into hydrogen by electrolysis and is stored in a metal hydride. Metal hydride beds are known for their high volumetric capacity compared to the compressed hydrogen storage, and offers hydrogen storage at a reasonable operating temperature and pressure. A system simulation model is developed in Matlab/Simulink platform for the dynamics of the metal hydride hydrogen storage system, which is charged by the wind energy. The thermal loads of the metal hydride storage system is met by passing water at ambient temperature for cooling the bed while hydrogen is being absorbed. The effect of the transient turbulent wind velocity profile on the storage system is analyzed. The thermal management of the storage system plays an important role in the overall design, and hence it is discussed in detail.

Model-based design of an automotive-scale, metal hydride hydrogen storage system

Sandia and General Motors have successfully designed, fabricated, and experimentally operated a vehicle-scale hydrogen storage demonstration system using sodium alanates. The demonstration system module design and the system control strategies were enabled by experiment-based, computational simulations that included heat and mass transfer coupled with chemical kinetics. Module heat exchange systems were optimized using multi-dimensional models of coupled fluid dynamics and heat transfer. Chemical kinetics models were coupled with both heat and mass transfer calculations to design the sodium alanate vessels. Fluid flow distribution was a key aspect of the design for the hydrogen storage modules and computational simulations were used to balance heat transfer with fluid pressure requirements. An overview of the hydrogen storage system will be given, and examples of these models and simulation results will be described and related to component design. In addition, comparisons of demonstration system experimental results to model predictions will be reported.

System simulation model for high-pressure metal hydride hydrogen storage systems

On-board hydrogen storage systems employing high-pressure metal hydrides promise advantages including high volumetric capacities and cold start capability. In this paper, we discuss the development of a system simulation model in Matlab/Simulink platform. Transient equations for mass balance and energy balance are presented. Appropriate kinetic expressions are used for the absorption/desorption reactions for the Ti 1.1CrMn metal hydride. During refueling, the bed is cooled by passing a coolant through tubes embedded within the bed while during driving, the bed is heated by pumping the radiator fluid through same set of tubes. The feasibility of using a high-pressure metal hydride storage system for automotive applications is discussed. Drive cycle simulations for a fuel cell vehicle are performed and detailed results are presented.

Catalyzed Light Hydride Nanomaterials Embedded in a Micro-Channels Hydrogen Storage Container

Activated alloys synthesized by arc-melting were examined as catalysts for improving the hydrogen sorption characteristics of nanostructured magnesium hydride, proposed as a reversible hydrogen storage material. The MgH(2)-catalyst absorbing materials were prepared by ball milling of pure MgH(2) with hydrided Zr(47)Ni(53), Zr(9)Ni(11), and other alloys investigated. The nanostructured MgH(2)-intermetallic systems were tested at 250 degrees C and catalyst addition of eutectoid Zr(47)Ni(53) resulted in the fastest desorption time and highest initial desorption rate. The catalyzed Mg-hydride with activated Zr(9)Ni(11) and Zr(7)Ni(10) phases showed fast desorption kinetics. Moreover, the results demonstrated that the composition of dispersed Zr(x)Ni(y)catalysts has a strong influence on the amount of accumulated hydrogen and desorption rate of Mg-nanocomposite. Part two covers advanced micro-channels hydrogen storage module design based on the results of semi-empirical computer simulations of heat and mass transfers in the container. The micro-channels reservoir concept offers many advantages over the conventional metal hydride hydrogen storage system. It is a micro-structured system that can pack a lot of power into a small space and dissipate effectively the heat of the sorption reactions. This review summarizes recent patents related to CNTS.

Experimental and numerical analysis of dynamic metal hydride hydrogen storage systems

This paper examines the dynamics of metal hydride storage systems by experimentation and numerical modelling. A specially designed and instrumented metal hydride tank is used to gather data for a cyclic external hydrogen load. Thermocouples provide temperature measurements at various radial and axial locations in the metal hydride bed. This data is used to validate a two-dimensional mathematical model previously developed by the authors. The model is then used to perform a parametric study on some of the key variables describing metal hydride systems. These variables are the equilibrium pressure, where the tails and concentration dependence are investigated, and the effective thermal conductivity of the metal hydride bed, where the pressure and concentration dependence are analyzed. Including tails on the equilibrium pressure curves was found to be important particularly for the accuracy of the initial cycles. Introducing a concentration dependence for the plateau region of the equilibrium pressure curve was found to be important for both pressure and temperature results. Effective thermal conductivity was found to be important, and the inclusion of pressure and concentration dependence produced more precise modelling results.

Two Dimensional Model for the Design of Metal Hydride Hydrogen Storage Systems

A 2-D mathematical description of a metal hydride hydrogen storage vessel was developed. This 2-D model was calibrated against experimental discharge data obtained from a commercially viable system containing Lm1.06Ni4.96Al0.04 metal hydride. The model was capable of predicting the performance of the vessel for both the discharge and charge processes over a wide range of conditions. This model should thus be very useful for the design and development of the next generation of metal hydride hydrogen storage systems.

Simulation of a thermally coupled metal-hydride hydrogen storage and fuel cell system

For the first time, the dynamic behavior of a thermally coupled hydrogen storage and fuel cell system was studied using experimentally validated models of a metal-hydride hydrogen storage system and a proton exchange membrane (PEM) fuel cell stack. Two specific situations were studied: in the first scenario, the fuel cell and metal hydride bed were thermally coupled; in the second scenario, they were thermally uncoupled. The results from these simulations clearly exposed unique and subtle behavior associated with thermally coupled systems that could not be easily gleaned from simulating each device alone, as revealed from studying the uncoupled case. The most important result exemplified the importance of providing waste (excess) energy from the PEM fuel cell to the metal hydride bed to facilitate the removal of hydrogen during a discharge process. A detailed parametric study is forthcoming.

Hydrogen drive for road vehicles-results from the fleet test run in Berlin

Years of basic research carried out at Mercedes-Benz to find solutions for the storage of hydrogen in metal hydrides and for running of internal combustion engines on hydrogen as well as the experience gained from several experimental vehicles formed the basis for a fleet test. As part of the project sponsored by the German Federal Ministry for Research and Technology (BMFT) ten vehicles were taken into operation in Berlin between October 1984 and June 1985. After one and a half years of testing, a positive conclusion can be drawn. A total of 160,000 km has been covered up to now. The malfunctions which arose in the vehicles and at the filling station were within the acceptable limits of such a test. The following accompanying tests were carried out in addition to the operational tests: • - regular check of emission and fuel consumption characteristics • - testing the metal hydride hydrogen storage system used in the vehicles • - determination and analysis of the data obtained during the fleet test. Problems are not foreseeable for the further course of the large-scale test due to run until the end of March 1988.