Metal Hydride Reactor Research Articles

Performance analysis of metal hydride heat pump system with CFD modelling development and actual reactor designs

Hydrogen and metal hydride reactions in a decarbonized heat pump system with low-grade waste heat recovery offer a promising path for sustainable energy storage and conversion. Based on actual metal hydride reactor designs, this study developed a 2D transient Computational Fluid Dynamics (CFD) model for such a heat pump system working with hydrogen and a metal hydride alloy pair of Zr0.9Ti0.1Cr0.6Fe1.4 and LaNi4.25Al0.75. The effects of operating temperatures on the coefficient of performance (COP) and specific heat power (SHP) of the system have been presented and analyzed. Subsequently, raising the medium-temperature heat sink (TM) from 358.15 K to 373.15 K, and low-temperature heat source (TL) from 308.15 K to 323.15 K, results in a decrease in the COP by 25.57%, and an increase in the COP by 38.2%, respectively. An optimum value of high-temperature heat source (TH) exists at 493.15 K for a maximum COP. In addition, the higher thermal conductivity increases the absorption and desorption capacity of hydrogen.

Experimental study on absorption and desorption behavior of a novel metal hydride reactor for stationary hydrogen storage applications

Metal hydrides have captured significant attention for hydrogen storage because of their high energy density and safety. However, the performance of these systems is largely influenced by the design of the storage reactor. In this perspective, a novel compact, lightweight, and effective multi tube MH reactor was designed, fabricated, and experimentally tested. The absorption and desorption behavior of the newly developed Ti0.9Zr0.1Mn1.46V0.45Fe0.09 alloy using the proposed MH reactor for hydrogen storage applications was analysed. At 30 bar supply pressure, the MH reactor absorbed 164.3 g (1.58 wt.%) of hydrogen in 894 s and delivered specific energy at an average rate of 94.7 W/kgMH. Further, the reactor released 153.6 g (1.48 wt.%) of hydrogen in 2246 s, when the desorption temperature was set at 50 °C. Moreover, the parametric study revealed that by raising the supply pressure from 10 bar to 20 bar and 30 bar, the stored capacity was improved by 11 % and 18.9 %, respectively, whereas the absorption time was drastically reduced by 43 % and 61.5 %, respectively. Furthermore, the fabricated reactor achieved gravimetric and volumetric storage densities of 0.75 % and 20.6 kg/m3 of H2. Also, the MH reactor achieved a maximum hydrogen storage efficiency of 82.3 %. Finally, the comparative results indicated that the MH reactor studied in this work demonstrated a faster hydrogen release rate compared to other medium to large capacity MH reactors reported in the literature.

Performance improvement of magnesium-based hydrogen storage tanks by using carbon nanotubes addition and finned heat exchanger: Numerical simulation and experimental verification

One of the important tasks of improving the properties of metal hydride reactors is the design of system with optimized heat and mass transfer. Many works are devoted to the selection of the optimal heat exchanger for metal hydride hydrogen storage systems. At the same time, it is necessary to consider the composition of the metal hydride bed, which affects thermal conductivity as well. Little attention has been paid to the study of heat transfer properties in hydrogen storage systems with a heat exchanger and a metal hydride bed based on magnesium hydride and carbon nanotubes. In this work we used numerical simulation to determine the effectiveness of carbon nanotubes addition and heat exchangers with different fin number and geometries on high-temperature magnesium-based hydrogen storage tanks performance. It was found, that increasing the number of fins from three to five makes a smaller contribution in the temperature increasing as compared to the addition of three fins to the heater. The three solid, radial and complex fins have a similar effect on the average Mg/MgH2 bed temperature at 60 min. The most optimal fin number and geometry is three radial fins in terms of the efficiency and the volume it occupies. The addition of carbon nanotubes increases the average temperature of the Mg/MgH2 bed by 67 K for a reactor equipped with a heater without fins. Hydrogen storage system with three radial fins and Mg/MgH2 bed enhanced with carbon nanotubes provides an increase in the average bed temperature of about 180 K as compared to system without fins and nanotubes. This leads to a reduction in the hydrogen absorption time to reach 90% saturation by almost 63% for the three radial fins reactor with carbon nanotubes addition to the metal hydride bed. It has been confirmed that the addition of carbon nanotubes to Mg/MgH2 makes a significant contribution to the heat transfer in the metal hydride bed. In addition, it is shown that both an increase in the heat transfer area and the thermal conductivity coefficient leads to a significant improvement in the efficiency of the metal hydride reactor. In the future, the obtained results can be taken into account when designing hydrogen storage systems based on these materials.

Performance optimization of hydrogen storage reactors based on PCM coupled with heat transfer fins or metal foams

Metal hydride is a type of solid hydrogen storage material that offers excellent hydrogen absorption and desorption reaction properties. However, there is a strong thermal effect during the reaction process when the materials are applied in reactors. Thus, effective thermal management techniques are crucial for promoting efficient reactions. Prior studies on the subject have shown that phase change materials can be coupled with metal hydride reactors to transfer the reaction heat. To further enhance the transfer of heat and reaction efficiency of the metal hydride reactors based on phase change materials, this study explored heat transfer enhancement methods on the phase change materials side, including adding heat transfer fins and discussing the fin parameters and composite foam metal. The findings of the study showed that in comparison to the reactor without fins, the absorption rate of adding 10 sets of fins can increase by 28%, and as the number of fins increased to 14, this value could increase to 39.4%. The use of Y-shaped fins did not substantially improve the reaction rate, mainly due to the sufficient number of straight fins, and the heat transfer area reaching the limit of the fin enhanced the process of heat transport. Thus, the improved method of using copper foam is further considered. Compared with the reactor with and without fins, the absorption rate of the copper foam coupled reactor is increased by 23.4% and 61.3%, respectively.

Understanding Solid Oxide Fuel Cell Hybridization: A Critical Review

A holistic literature review of 399 articles is presented on hybrid solid oxide fuel cell (SOFC) systems and taxonomized through a unique classification methodology that considers primary energy sources, component configurations, system outputs and relevant analysis. In the reviewed research articles, primarily four different types of technologies are used to complement the energy production of the fuel cell stack. As a result, four respective categories were established in terms of the coupling components, inclusive of (1) wind turbines (WTs), (2) solar systems (SS), (3) thermal power plant turbines (TPPTs) and (4) piston engines (PEs). Additional classification was needed to further subdivide the evaluated system configurations, due to the wide spectrum of system outputs encountered in the reviewed literature. That involved (a) electrical power generation (PG), (b) four types of cogeneration (CG), (c) four types of trigeneration (TG) and (d) two types of multigeneration (MG). Depending on the type of assessment in respective research, literature was further categorized as computational, experimental, or both computational and experimental. The most prevalent hybrid system amongst the 102 designs, as adapted from the reviewed literature, is the SOFC/gas turbine (GT) application, with the overwhelming majority producing exclusively electrical power output. The particular system is physically demonstrated in an existing 220-kW experimental facility established by the National Fuel Cell Research Center (NFCRC). The identified systems were predominantly computationally examined and research focused on operating conditions around specific design load ratings. Energy, exergy, economic, and environmental assessments were typically followed by sensitivity studies in the reviewed literature. The primary decision variables in most cases revolved around SOFC operating conditions, such as temperatures over 1000 °C as well as elevated pressures. Those resulted in the deterioration of the electrochemical cell and failed to be addressed by the majority of encountered studies. Improvements in the conversion efficiency of PG applications were enabled by natural gas (NG)-fed pressurized SOFCs, directly coupled to GTs. The most efficient power configuration in terms of thermodynamic performance was achieved by coupling PEs to SOFCs and a metal hydride reactor (MHR) to unlock a maximum net system efficiency of 79.54%. CG systems integrating solar cells (SCs) and photovoltaic panels (PVs) to SOFC subsystems can result in a combined efficiency of approximately 90% and sustain this over a broad energy demand range. TG systems incorporating gasifiers to SOFC/GT subsystems achieved a combined efficiency of 93%, whereas the optimal combined efficiency in MG configurations was identified at 79.5% by coupling SCs to the SOFC/GT/organic Rankine cycle turbine (ORCT) subsystems. In terms of cost-effectiveness, configurations that relied on increasing levels of renewable energy (RE) technologies resulted in high overall levelized cost of electricity (LCOE). This cost was increased further when power storage units were deployed to address wind and solar intermittency challenges. Configurations classified under TPPTs operating on low carbon-content fuels were preferred in terms of providing lower LCOE, while applications operating on gasified biomass and coal blends should deploy additional CO2 capture and storage units to mitigate respective emissions.

Optimization on distribution of high thermal conductivity materials in metal hydride reactor for improving heat transfer performance

The poor heat transfer performance significantly limits the reaction rate of hydrogen storage and release in metal hydrides reactors. In this work, the expanded graphite was used as high thermal conductivity materials (HTCMs), its optimal distribution in metal hydrides reactor was obtained by topology optimization method to enhance the heat transfer performance. Comparative studies on the hydrogen storage and release performance were conducted for the optimal HTCMs distribution model, uniform HTCMs distribution model, reconstructed model, and unimproved model to validate the optimization results. Finally, the effect of HTCMs contents was also studied. The results show that the optimization results shorten the hydrogen storage and release time by 32.3 % and 15.9 %, respectively, compared to the uniform distribution model. Besides, the proposed optimization scheme exhibits good performance under different HTCMs contents. When the content was set to 12 %, the optimized model reduces the hydrogen storage and release time by 28.5 % and 10.8 %, compared to the results of uniform distribution. The method and results of topology optimization have high reliability, and the HTCMs distribution designed by topology optimization has better hydrogen storage and release performance compared to original designs, it is widely applicable.

Compressor‐Driven Titanium and Magnesium Hydride Systems for Thermal Energy Storage: Thermodynamic Assessment

ABSTRACTMetal hydrides enable excellent thermal energy storage due to their high energy density, extended storage capability, and cost‐effective operation. A metal hydride‐driven storage system couples two reactors that assist in thermochemical storage using cyclic operation. Metal hydride reactors, operating at both low and high temperatures, serve for the storage of hydrogen and thermal energy, respectively. The integration of efficient thermal energy storage technology is known to enhance the efficiency of solar thermal systems. In this regard, during the peak hours of solar energy, the high‐temperature supply heat can be utilized to store hydrogen gas in the low‐temperature reactor, which simultaneously facilitates energy storage in the high‐temperature reactor. Moreover, the temperature and energy released from the reactors are highly dependent on the pressure of the gas. As a result, installing a compressor between the low and high‐temperature metal hydride reactors can help generate additional outputs, such as a cooling effect. This paper conducts a thermodynamic analysis to assess the system's performance, considering parameters such as thermal storage efficiency, coefficient of performance (COP), and COPCCH (combined cooling and heating based COP). Moreover, the performance analysis was carried out for two cases, that is, high‐temperature titanium hydride (TiH2) and magnesium hydride (MgH2). The results show that MgH2 and TiH2 achieve a maximum COPCCH of 1.08 and 0.9, respectively, and system storage efficiency of 76.15% and 74.34%, respectively. In spite of having lower efficiency than MgH2, the TiH2‐based system has the ability to recover heat at a very high temperature.

Strategic integration of metamaterials properties and topology optimization of gyroid metal hydride reactor for high-density hydrogen storage

Metal hydride (MH) is considered to be one of the potential materials for storing hydrogen. It has a substantial limitation to wide use in the mobility sector, which is its low gravimetric hydrogen storage density. A novel canister design utilizing the optimization of gyroid structure for MH-based hydrogen storage is proposed to enhance reactor strength and capacity, increasing the favor of using it outside stationary applications. Topology optimization (TO) of the reactor increases the capacity by 49 % while maintaining the capability of this reactor to sustain 5000 N of bending case. On top of that, changing the metamaterial properties of the gyroid results in a larger chamber size for storing a larger amount of MH by the maximum amount of 30 %. However, increasing the chamber size comes with a cost of a lower charging rate and a considerable area of non-reacted hydride at the same charging time compared to the non-modified structure. By evaluating the MH bed that consists of lanthanum nickel (LaNi5), the topologically optimized reactor design is varied with different chamber offsets of 0, 2, and 4 mm. The results show that using a 2 mm offset in this study case can increase hydrogen storage capacity by 22 % while maintaining the same charging time of less than 4500 s. The combination of both proposed methods can increase the overall MH bed chamber by 66.22 % compared to previous initial research that acts as proof of concept.

Effect of partition arrangement of metal hydrides and phase change materials on hydrogen absorption performance in the metal hydride reactor

Metal hydride (MH) suffers from strong thermal effects during hydrogen absorption. To fully utilize the reaction heat during hydrogen absorption, phase change material (PCM) can be used to achieve efficient thermal management in the reactor. A novel MH-PCM reactor with the partition arrangement of MH and PCM was proposed in this paper. Then, the two-dimensional multiphysics coupled model of the reactor was developed, and the effects of the number of partitions n, the mass of PCM and the hydrogen absorption pressure Pa on the hydrogen absorption performance were discussed detailedly. The results indicated that the novel MH-PCM reactor not only increases the heat transfer area and boots the hydrogen absorption rate, but also improves the uniformity of temperature distribution. As the n increases from 2 to 5, the hydrogen absorption time gradually shortens. Compared to the conventional MH-PCM reactor, the time for 90% hydrogen absorption shortens by 67.13%. Furthermore, the hydrogen absorption rate can be enhanced with the increasing mass of PCM and Pa. However, the larger these values are, the weaker the enhancement effect becomes. The results of this paper may provide a new direction for the optimized design and engineering application of MH-PCM reactors.

Exploring hydrogen storage safety research by bibliometric analysis

The application of hydrogen energy is affected by the safety of hydrogen storage system. To grasp the current status of research and application in the research field of hydrogen storage safety and explore its research development trend, data analysis techniques, such as co-occurrence, co-citation, and burst detection, were adopted to conduct bibliometric analysis of the relevant literature. The study results show that the research hotspots of hydrogen storage safety mainly concentrate on six aspects: the stability of metal hydride hydrogen storage materials, the study of thermal management and stress relief in metal hydride reactors, the safety analysis of hydrogen fuel cells and hydrogen leakage monitoring, the analysis of leakage and explosion risks in hydrogen refueling stations, the study of filling pressure and temperature distribution in hydrogen storage tanks, and the study of safety issues in underground hydrogen storage. Mg-based hydride stability and underground hydrogen storage risk analyses are current research frontiers in hydrogen storage safety.

Influence of corrugated tube structure and flow rate on the hydrogen absorption performance of metal hydride reactor and structural optimization

The metal hydride bed (MHB) reactor is an effective instrument for storing hydrogen. However, thermal stress causes the cooling tube expansion inside the MHB. The long-term effects will lead to the failure of the cooling tube. To absorb the thermal stress and reduce the deformation of the cooling tubes, this article establishes an MHB reactor with corrugated cooling tubes to study its hydrogen absorption performance. The results prove that some parameters are adversarial and flow rate patterns are complex (such as extreme flow rate and insufficient flow rate) in the hydrogen absorption process of the corrugated tube MHB reactor, which makes it impossible to optimize the structure of the corrugated tube through the gradient method. Under the condition of a fixed corrugated tube volume of 3×10−6m3 and a cooling water volumetric flow rate of 0.5×10−4m3/s, the structural parameters of the corrugated tube are optimized by the Monte Carlo algorithm. According to the optimized results (N=8, ro=4.25 mm, ri=3.98 mm, do=3.17 mm, di=4.33 mm), the hydrogen absorption efficiency of the corrugated tube MHB reactor (reaction fraction 0.758) is 1.36 times that of the straight tube (reaction fraction 0.557) at 560 s. Thus, the corrugated tube can reduce thermal stress and improve the heat transfer effect. This research is beneficial in improving long-term stability, enhancing operational efficiency, and reducing the volume and weight of large MHB reactors.

AB5-based metal hydride embedded in polyethylene and polymethylmethacrylate for hydrogen storage

Loose powder in metal hydride reactors poses challenges, such as poor thermal conductivity and tube deformation. To address these issues, the metal powder can be encapsulated in a polymer-based matrix to form pellets. This encapsulation helps make the pellets oxygen-impermeable, capable of accommodating the volumetric expansion of metal hydrides, and increases system processability. This study investigates the use of polymer-based pellets containing AB5-based compounds for ambient hydrogen storage. Polymers were selected using ANSYS Granta software, and polyethylene and polymethylmethacrylate were chosen. The AB5 alloy activation in the pellet occurs efficiently after 3 min at 20 °C and 30 bar of hydrogen, facilitated by ball milling-induced reactive surfaces and increased grain boundaries. The optimized pellet, comprising 90 wt% AB5 powder in a PE matrix, exhibits stable hydrogen storage properties, with good mechanical resistance and minimal powder loss (below 3%) over 20 hydrogen sorption cycles in an in-house fabricated single-tube metal hydride reactor.

Hydrogen storage systems performance and design parameters using response surface methods and sensitivity analysis

DesignDesign of metal hydride-based hydrogen storage reactors is often performed using numerical/experimental modelling which is computationally/economically difficult. This paper investigates the applicability of Response Surface Methodology (RSM) coupled Local/Global Sensitivity Analysis (L/GSA) to investigate – i) the applicability of advanced RSMs in predicting the responses for storage systems efficiently, ii) the applicability of advanced RSMs to perform L/GSA to identify the sensitive input design parameters based on their effect on the Outputs of Interests (OIs), i.e., reaction fraction (i.e., C) and bed temperature (i.e., T), and iii) the dependence of importance ranking of design parameters on the employed L/GSA methodology. The study is conducted in two stages. In the first stage, the most accurate RSM was identified among fourteen traditional and advanced RSMs, i.e., radial basis, kriging, quadratic, moving least square, support vector machine etc., employing a measure of precision, i.e., Nash–Sutcliffe Efficiency (NSE). RSMs were constructed based on the values of OIs estimated using finite element simulation using COMSOL software for random realizations of inputs generated via Latin Hypercube Sampling (LHS). In the second stage, the importance ranking of design parameters was estimated for both OIs using six different L/GSAs based on the input-output relationships estimated in stage one. All the codes of RSMs and L/GSAs were written and validated in MATLAB. Finite element simulations of the random realizations were performed using COMSOL software. For the present study, NSEs of the considered RSMs were ranging between 0.6262-0.8544 and 0.4652–0.8081 for C and T respectively, indicating the importance of selection of appropriate RSM. RBF-augmented Compact-I and kriging were the most accurate RSMs with NSEs approximately 10%–20 % higher to those of frequently used polynomial RSM. Time (t) and mass of hydrogen to be stored (MH) were the most; and external temperature (Text) and porosity (E) were the least sensitive inputs corresponding to C and T, with differences of 80–90 % in the sensitivity indices respectively. The ranking prediction was highly dependent upon the employed L/GSA methodology, with Morris's screening observed to be the least accurate. The RSM methods described in this study help to design and investigate the metal hydride reactors for various applications (space heating, hydrogen storage, storage for vehicular application, metal hydride compressor) without undergoing detailed mathematical modelling of the system. The proposed methodology may significantly assist the designers to focus (or vary) on the sensitive inputs only during the physical modelling of systems to improve their performance. This sensitivity analysis is helpful to find out the most advance sensitivity analysis method which can be used to find out the most sensitivity parameter which can be varied according to their rankings to achieve the required performance of metal hydride reactor for the particular application. The advanced RSMs assist to identify these sensitive inputs quickly by reducing the mathematical efforts in the L/GSA by providing the accurate input-OIs relationships based on the limited numerical simulations. This will significantly save the resources and time of industries required in physical modelling/numerical simulations significantly, which otherwise would have been invested on investigating the non-sensitive inputs.

Experimental and numerical investigations on synergistic coupling of metal hydride hydrogen storage systems with low-temperature proton exchange membrane fuel-cell

Hydrogen has emerged as a promising alternative for various energy needs, and metal hydride hydrogen systems offer significant potential due to their near-ambient working conditions and safe storage. This study presents experimental and numerical investigations on a lab-scale metal hydride fuel cell system to showcase its viability in addressing future energy demands. The experimental setup includes a 41-tube Metal Hydride (MH) reactor with an outer cooling jacket, containing 3.75 kg of La0.7Ce0.1Ca0.3Ni5. The output of the reactor is coupled to a 1 kW fuel cell, with controlled hydrogen discharge at temperatures ranging from 30 to 50 °C through numerical modelling. The study found that maintaining the reactor at 40 °C was sufficient to sustain the required bed pressure for a 1 kW fuel cell. Numerical simulations revealed that a 1 kW fuel cell operating at a current density of 0.8 A/cm2 and 50 °C rejected approximately 1.3 kW of waste heat. Moreover, 3.75 kg MH reactor could discharge hydrogen at a constant rate of 13 l/min for 36.3 min with just 125–225 W of heat input, highlighting the thermal coupling potential between these systems. The energy efficiency of the coupled MH-PEMFC system increased by 1.8 times to reach 49% at 50 °C. Additionally, the waste heat generated proved sufficient to provide the required endothermic heat to multiple MH reactors, with a single reactor utilizing only 16.3% of the total waste heat. This integrated system demonstrates promising efficiency and sustainability for future energy applications.

Impact of fins and cooling fluid on the hydrogenation process in a LaNi5-Based metal hydride reactor for hydrogen storage

This study investigates the influence of different reactors incorporating copper circular fins within the hydride, along with variations in the reactor coolant—specifically water, oil, and nitrogen. Employing user-defined functions in the commercial software Ansys Fluent 15, a 2D numerical model was developed to assess thermal characteristics (temperature, heat flux, etc.) and kinetics of MH-hydrogenation, with a focus on the cooling fluid type. The reactor experiences diverse pressures (5–15 bar), an initial temperature of 298 K, and a coolant speed of 1 m/s. Validation of numerical results was performed against experimental data. The study delves into absorption properties of the storage reactor, examining crucial parameters such as hydrogen concentration, heat transfer coefficient of forced convection, and average temperature within the reactor. The findings reveal that coupling internal fins with water or oil as a coolant yields optimal performance, especially on an industrial scale. Nitrogen, on the other hand, exhibited the least favorable thermal performance, while the addition of fins significantly improved the cooling performance of the storage unit. Results were quantitatively analyzed across various scenarios to enhance understanding of the synergistic role of fins and cooling fluids in the storage performance of H2 within LaNi5 alloy.

Thermal management techniques for enhancing hydrogen adsorption and desorption in metal hydride reactors: a short recent review

This manuscript presents a short recent review of various techniques used for thermal management enhancement in metal hydride reactors, emphasizing their effect on hydrogen adsorption and desorption. Mainly, the article highlights 4 techniques: The incorporation of various fin types, the integration of heat exchangers within the metal hydride reactor, the addition of heat transfer enhancing material into the MH bed, and the addition of phase change material (PCM). The analysis presented provides brief insightful information about the state of Metal hydride reactors now, laying the groundwork for future studies and advancements in this area.

Experiment and model results of a first bidirectional active temperature control module with metal hydrides for a fuel cell

Many temperature control techniques are based on active heating and passive cooling and thus have a lack of active bidirectional controllability. Whereas, several applications need a precise bidirectional temperature control. The present study demonstrates a novel bidirectional and active temperature control unit (TCU). This unit heats and cools a fluid with the reversible reaction between metals and hydrogen. The reaction of metal hydrides is characterized by a pressure temperature correlation. Hence, the thermal power and the temperature can be regulated by the gas pressure in the TCU. This enables temperature controllers with the pressure as actuating variable on the metal hydride. In this study, an existing LaNi5 reactor is modelled as 0D model. A PID controller is implemented in the simulation and in the experimental setup to stabilize the temperature with the regulation of the pressure in the reactor. Results from experiment and simulation show the stabilization of the temperature.

Performance improvement of metal hydride hydrogen compressors using electromagnetic induction heating

While there are some hydrogen refueling stations (HRS) functioning in different parts of the world, their use is not widespread enough, primarily due to their expensive cost. Hydrogen compression is a main contributor to the capital and operation costs of the HRS. By improving H2 compression technology, it is possible to optimize the infrastructure for refueling with hydrogen in terms of cost and performance. The use of metal hydride hydrogen compressors (MHHCs), which have the potential to be inexpensive and have the ability to use waste heat and renewable energy sources for the H2 compression, is a promising solution to overcome this issue. The duration of the H2 compression cycle is nevertheless a serious challenge due to the metal hydride (MH) bed's low heat conductivity. As a heating technique to improve the performance of MHHCs, electromagnetic induction (EMI) is examined numerically for the first time in this work. The dynamic behavior of a two-stage MHHC with each MH reactor having an external heat exchanger and being ringed by a copper coil traversed by an alternating current is described by a two-dimensional mathematical model, which was established and successfully verified by the reference data. Numerical simulations were performed with the help of this model, and the findings showed that the EMI heating method is faster than the heat transfer fluid (HTF) heating technique. For instance, at a delivery temperature of 373 K and a supply pressure of 20 bar, it is possible to produce 106 NL H2 per kilogram of HPMH at a pressure of 97 bar with a 74 % shorter compression time than with the HTF heating technique.

CFD simulation of heat and mass transfer processes in a metal hydride hydrogen storage system, taking into account changes in the bed structure

CFD modelling of heat-and-mass transfer in metal hydride (MH) beds is an important step in the development and optimisation of MH reactors for hydrogen storage, compression and separation/purification. In the existing models, the mass conservation equation includes the density of solid in the non-hydrogenated (ρs) and hydrogen-saturated (ρss) states. To provide constant porosity of the MH bed during H2 absorption/desorption, assumption ρs<ρss is typically taken. However, this assumption contradicts to well-known fact that hydrogenation of hydride-forming alloys is accompanied by the expansion of crystal lattice of the metallic matrix and, therefore, by the decrease of the solid density by 15–25%.This work presents results of the modelling which takes this effect into account. The model assumes that the density of the MH changes linearly as the starting hydride-forming alloy is saturated with hydrogen, while the volume of the MH bed remains constant. The last assumption is a limiting estimation because it provides the maximum possible reduction in the porosity during H2 absorption process.The model was validated using published experimental data on a cylindrical MH reactor filled with 422 g of LaNi5. It was shown that accounting the realistic changes in the MH density can significantly affect the simulation results.

Topology optimization of gyroid structure-based metal hydride reactor for high-performance hydrogen storage

Numerous engineering applications stand to gain substantial advantages by mitigating structural weight. While methods for optimizing continuous solids and discrete frame structures have long been available, the advent of additive manufacturing techniques has ushered in the potential for intricate geometries. In contrast, the hydrogen fuel sector confronts a pivotal challenge: the need to develop efficient hydrogen storage systems. Solid-state compounds like metal hydrides (MH) present a compelling solution among various hydrogen storage technologies thanks to their inherent safety attributes and superior hydrogen volumetric density. Nonetheless, the limitation of MH lies in its gravimetric density, impeding its application in mobility contexts. A transformative strategy addresses this limitation by seamlessly integrating the reactor tank into the vehicle's frame and chassis. This study introduces a pioneering concept—an optimally designed MH container incorporating a gyroid structure. Subsequently, this innovative design underwent rigorous analysis, employing finite element analysis (FEA) and computational fluid dynamics, assessing mechanical properties, heat transfer capabilities, and the efficiency of hydrogen charging into the MH within the structure. Using topology optimization of solid isotropic material with penalization method, a 17 % increase in the chamber volume and a concurrent reduction of the material by nearly 50 %. This profound transformation positively impacted the reactor's volumetric and gravimetric density. Despite a measurable reduction in strength, the optimized structure demonstrated resilience, successfully withstanding prescribed mechanical shear loads. Furthermore, the structure exhibited impressive rigidity, with displacement below 0.2 mm, rendering it suitable and highly competent for integration into assembly components like vehicle frames or chassis. Notably, the optimized structure exhibited a promising enhancement in hydrogen charging rate.