Hydrogen Supply Pressure Research Articles

Thermal Modeling of Mg2Ni-Based Solid-State Hydrogen Storage Reactor

In this paper, a numerical study of coupled heat and hydrogen transfer characteristics in an annular cylindrical hydrogen storage reactor filled with Mg2Ni is presented. An unsteady, two-dimensional (2-D) mathematical model of a metal hydride reaction bed of cylindrical configuration is developed for predicting the hydrogen storage capacity. The effect of volumetric radiation is accounted in the thermal model. Effects of hydride bed thickness, initial absorption temperature, hydride bed thermal conductivity, and hydrogen supply pressure on the hydrogen storage capacity are studied. A thinner hydride bed is found to enhance the hydriding rate, accomplishing a rapid reaction. At an operating condition of 20 bar supply pressure and 573 K initial absorption temperature, Mg2Ni stores about 36.7 g hydrogen per kg alloy. For a given bed thickness and an overall heat transfer coefficient, there exists an optimum value of hydride bed thermal conductivity. The present numerical results are compared with the experimental data reported in the literature, and good agreement was observed.

Tests on LmNi4.91Sn0.15 based solid state hydrogen storage device with embedded cooling tubes – Part A: Absorption process

In Part A of this manuscript which consists of two parts, the experimental investigations pertaining to the absorption of hydrogen in an LmNi4.91Sn0.15 based solid state hydrogen storage device with embedded cooling tubes (ECT) are presented. Two metal hydride based hydrogen storage devices with 36 and 60 ECT filled with 2.75 kg of LmNi4.91Sn0.15 were fabricated. Performances of the hydrogen storage devices in terms of hydrogen absorption rate and amount of hydrogen absorbed are reported for different supply pressures (10–35 bar), absorption temperatures (20–30 °C) and cooling fluid flow rates (2.2–30 l/min). At any given absorption temperature, the rate of hydrogen absorption and the amount of hydrogen absorbed are found to increase with hydrogen supply pressure up to about 35 bar. At the supply condition of 35 bar hydrogen pressure and 30 °C absorption temperature, with oil as a heat transfer fluid at a flow rate of 3.2 l/min, the maximum amount of hydrogen absorbed are ≈1.18 wt% in 10 min for 36 ECT, and 8 min for 60 ECT. At the absorption condition of 25 bar supply pressure, 30 l/min water flow rate and 30 °C absorption temperature, the absorption time of the reactor with 60 ECT was reduced to 5 min.

Performance simulation and experimental confirmation of a mini-channel metal hydrides reactor

A theoretical and experimental study about a proposed mini-channel reactor was carried out to enhance heat transfer performance for metal hydrides applications, such as hydrogen storage, hydrogen compression and chemical heat pumps. The configuration of the reactor and working principles are described in detail. The predicted hydride bed temperature profiles in the reactor are compared with the experimental data from the performance test system, and a reasonable agreement is observed. The simulation of the hydrogen adsorption and desorption processes in a mini-channel reactor packed with LaNi5 is conducted, and the influences of some important parameters, e.g. the bed thickness, the number of the mini-channels, hydrogen supply and discharge pressure are analyzed. Comparing with the traditional reactors, such as tubular reactor and disc reactor, the mini-channel reactor has some obvious advantages, therefore can be recommended for applications.

Simulation studies on heat and mass transfer in high-temperature magnesium hydride reactors

Magnesium hydride is one of the most promising materials for hydrogen storage and high-temperature heat storage. The heat and mass transfer processes occurring in magnesium hydride reactors are very complicated. In the present study, a mathematical model for a magnesium hydride reactor is developed to investigate the mass and heat transfer characteristics under various operating conditions. The distributions of gas velocity, gas pressure, temperature and reacted fraction are obtained by solving the rigorous model. Two versions of the model, which are respectively applied on two different computational domains, are investigated. The simplified version of the model is proved capable of predicting the performance of the magnesium hydride reactor, with high computation efficiency and acceptable accuracy. The simulation results indicate that an increase in hydrogen supply pressure (pin) accelerates the absorption process due to enhanced absorption reaction kinetics. The hydriding time decreases when heat transfer fluid (HTF) velocity (uf) goes up, because the convection heat transfer coefficient between HTF and the magnesium hydride rises with increasing HTF inlet velocity. Moreover, an increase in HTF inlet temperature (Tin) leads to an increase in the equilibrium pressure of the magnesium hydride which decelerates the hydrogen absorption reaction. The optimal setting of the three operating parameters for the magnesium hydride reactor is determined based on the mathematical model, and the corresponding values of the parameters are as follows: pin=2.6MPa, Tin=473K and uf=5ms−1.

Effects of reactor design on TiFe-hydride's hydrogen storage

SUMMARY The experimental investigation of TiFe-hydride has been performed for rapid and high-rate storage of hydrogen under low operating pressure. Three different reactors are designed, manufactured and tested to investigate the effect of reactor design. The reactors are a tubular-shaped simple one, a tubular-shaped reactor with fins and a tubular-shaped reactor with liquid cooling channels. All of the reactors are filled with same amount of TiFe alloy and charged under various hydrogen supply pressures. The charging time and the role of the heat transfer mechanism are investigated by obtaining temperature histories which are measured at several points on the reactors. It has been found that the reactor design and activation process of metal-hydride alloy are significant parameters on the amount of hydrogen stored in the reactor and the elapsed time for storing. The charging time was 84% less, and storage rate was 39% higher for Reactor-3 compared to Reactor-1. The hydrogen storage rate was approximately 0.44% which is achieved at relatively low charging pressure of 12 bar. Copyright © 2012 John Wiley & Sons, Ltd.

Experimental study on the hydrogen charge and discharge rates of metal hydride tanks using heat pipes to enhance heat transfer

Heat transfer is a critical factor affecting the performance of metal hydrogen storage tanks. Many studies have proposed inner tubular heat exchangers for increasing the heat transfer rate between the metal powders and the exterior environment of the tanks. However, connecting cooling and heating fluid tubes to the storage tanks can be a tedious task, especially for large-scale hydrogen storage systems with a large array of tanks. This study presents a novel design for a metal hydride vessel equipped with heat pipes. These heat pipes enhance heat transfer for hydrogen charge and discharge without the need for tubing through the metal bed. This study experimentally demonstrates the effects of using heat pipes to enhance heat transfer in a hydrogen storage tank using LaNi5 as the storage media and comparing tanks with and without heat pipes. Results show that heat pipes can enhance the hydrogen storage rates in both absorption and desorption. The absorption time was reduced more than half with a 10atm hydrogen supply pressure, and the desorption time for hydrogen discharge at 1L/min was increased by 44%.

Tests on a metal hydride based thermal energy storage system

In this paper, the performance tests on Mg + 30% MmNi4 based thermal energy storage device is presented. Experiments were carried out at different supply pressures (10–30 bar) and absorption temperatures (120–150 °C). The effects of hydrogen supply pressure and absorption temperature on the amount of hydrogen/heat stored and thermal energy storage coefficient are presented. The maximum hydrogen storage capacity of 2.5wt% is reported at the operating conditions of 20 bar supply pressure and 150 °C absorption temperature. For a given absorption temperature of 150 °C, the thermal energy storage coefficient is found to increase from 0.5 at 10 bar to 0.74 at 30 bar supply pressure. For the given operating conditions of 20 bar supply pressure and 150 °C absorption temperature, the maximum amount of heat stored is about 0.714 MJ/kg and the corresponding thermal energy storage coefficient is 0.74.

Study of coupled heat and mass transfer during absorption of hydrogen in MmNi4·6Al0·4 based hydrogen storage device

A two-dimensional numerical analysis of coupled heat and mass transfer processes in a cylindrical metal hydride reactor containing MmNi4·6Al0·4 is presented. To understand the hydrogen absorption mechanism the governing equations for energy, momentum and mass conservation and reaction kinetic equations are solved simultaneously using the finite volume method (FVM). Performance studies on MmNi4·6Al0·4 based hydrogen storage device are carried out by varying the hydrogen supply pressure, absorption (cooling fluid) temperature, overall heat transfer coefficient and hydride bed thickness. Effect of convection terms in the energy equation on hydrogen storage performance is found to be negligible. The results obtained from the computer simulation showed good agreement with the available experimental data. At the supply conditions of 30 bar and 298 K, MmNi4·6Al0·4 stores about 1·28 wt%, which is very close to the experimental value of 1·3 wt%. Overall high heat transfer coefficients are found to reduce the absorption time significantly.

Performance of air cooled hydrogen storage device with external fins

Minimization of total weight is the major criterion in the design of a solid state hydrogen storage device for mobile or portable applications. The design should also address the requirements such as storage capacity, charge/discharge rates, space constraints, coolant temperature and hydrogen supply pressure. To achieve this, one should be able to reliably predict the dynamic performance of the storage device. In this paper, a parametric study of hydrogen sorption in an air-cooled annular cylindrical hydrogen storage device with external fins is reported. LaNi 5 , which has excellent hydrogen storage properties is used as the hydriding material. The influence of different geometric parameters such as hydride bed thickness and fin height, and operational parameters such as hydrogen supply pressure and cooling air temperature are studied. Copyright , Manchester University Press.

Parametric studies on a metal hydride based hydrogen storage device

In this paper, a two-dimensional computational investigation of coupled heat and mass transfer process in an annular cylindrical hydrogen storage device filled with MmNi 4.6 Al 0.4 is presented using a commercial software FLUENT 6.1.22. Hydrogen storage performance of the device is studied by varying the operating parameters such as hydrogen supply pressure and absorption temperature. Further, the effects of various bed parameters such as hydride bed thickness and overall heat transfer coefficient on the storage performance of the device are also studied. The average temperature of the hydriding bed and hydrogen storage capacity at different supply pressures showed good agreement with the experimental data reported in the literature. It is observed that as the hydriding process is initiated, the absorption of hydrogen increases rapidly and then it slows down after the temperature of the hydride bed increases due to the heat of the reaction. At any given absorption temperature, the hydrogen absorption rate and hydrogen storage capacity are found to increase with the supply pressure. The variation in the hydrogen absorption capacity, rate of reaction and temperature profiles at different supply pressures from 5 to 35 bar in steps of 5 bar are presented. Further, the effects of overall heat transfer coefficients from 750 to 1250 W/m 2 K and cooling fluid temperatures from 288 to 298 K on hydrogen storage capacity are also investigated. It is shown that the heat transfer rate enhances the hydriding rate by accomplishing a rapid reaction. At the supply condition of 35 bar and 298 K, MmNi 4.6 Al 0.4 stores about 13.1 g of hydrogen per kg of alloy.