Hydrogen Supply Pressure Research Articles

Quantitative analysis of hydrogen leakage flow measurement and calculation in the on-board hydrogen system pipelines

The mass flow rate of hydrogen leakage directly affects hydrogen diffusion and concentration distribution. In this paper, a test platform was constructed to measure mass flow rates during hydrogen leakage in the supply pipelines of the on-board hydrogen system. Hydrogen leakage tests were conducted under two different conditions. Mass flow rates were measured for tube fittings with various loosening angles and hydrogen supply pressures. The data were then fitted to extrapolate mass flow rates of hydrogen leakage beyond the tested conditions. Additionally, mass flow rates were measured for hydrogen supply pipelines with small holes of different shapes and sizes. The effects of pipeline size, hydrogen supply pressure, hole shape, and size on the hydrogen leakage mass flow rate were analyzed. Hydrogen leakage flow coefficients were corrected, and the accuracy of three calculation methods for hydrogen leakage flow was compared and analyzed based on the test results. The results provide a foundation for future numerical simulation models of hydrogen leakage diffusion.

A parametric study on hydrogen storage in AB5 hydride alloys: Heat and mass transfer, thermodynamics, and design

The design of heat exchangers plays an important role in the performance of solid-state hydrogen storage devices. In this study, three different designs of hydrogen storage devices were investigated, incorporating phase change material (PCM), specifically, RT25HC into their walls in various shapes. A mathematical model, validated using previous experimental data, was employed to calculate heat and mass transfer and determine the reaction time period. The calculations were conducted using ANSYS Fluent, with a constant hydrogen supply pressure of 10 bars and a temperature of 295 K. The absorption properties of the storage reactor were investigated through various parameters such as liquid fraction, hydrogen concentration, and natural convection heat transfer coefficients. Results showed that the geometric structure and PCM distribution significantly impacted the performance of the hydrogen storage devices. Design 1, with a centralized PCM distribution, demonstrated moderate heat transfer rates and a longer reaction time. Design 2, featuring a more distributed PCM layout, improved heat transfer rates and reduced hydrogen kinetics time by 40%. Design 3, which optimized the geometric structure with advanced PCM shapes, achieved the highest heat transfer rates and improved hydrogen kinetics time by 50%. This design also enabled the storage of thermal energy at a high density, ranging from 10.2 J/g to approximately 190.5 J/g. The study provides critical information on the design of efficient solid hydrogen storage processes. The findings suggest significant potential for improved performance in industrial applications such as electric vehicles and domestic energy supply. The high efficiency of the large-scale reactor is due to its well-designed system, which effectively converts chemical energy into thermal energy. Optimizing the reactor geometry and PCM distribution is crucial for achieving superior hydrogen storage and retrieval performance.

Research Progress on Gas Supply System of Proton Exchange Membrane Fuel Cells

Proton exchange membrane fuel cells (PEMFCs) are attracting attention for their green, energy-saving, and high-efficiency advantages, becoming one of the future development trends of renewable energy utilization. However, there are still deficiencies in the gas supply system control strategy that plays a crucial role in PEMFCs, which limits the rapid development and application of PEMFCs. This paper provides a comprehensive and in-depth review of the PEMFC air delivery system (ADS) and hydrogen delivery system (HDS) operations. For the ADS, the advantages and disadvantages of the oxygen excess ratio (OER), oxygen pressure, and their decoupling control strategies are systematically described by the following three aspects: single control, hybrid control, and intelligent algorithm control. Additionally, the optimization strategies of the flow field or flow channel for oxygen supply speeds and distribution uniformity are compared and analyzed. For the HDS, a systematic review of hydrogen recirculation control strategies, purge strategies, and hydrogen flow control strategies is conducted. These strategies contribute a lot to improving hydrogen utilization rates. Furthermore, hydrogen supply pressure is summarized from the aspects of hybrid control and intelligent algorithm control. It is hoped to provide guidance or a reference for research on the HDS as well as the ADS control strategy and optimization strategy.

Numerical study of polymer embedded metal hydride-based self-sensing actuator

Metal hydride actuators have amassed increasing attention over the past decade owing to their desirable operational characteristics, such as a high power-to-weight ratio, noiseless and vibration-less operation, lightweight, safety and environmental friendliness. Essentially, there are two ways in which we can attain actuation using hydrides. Primarily, actuation force is generated by the hydrogen gas pressure changes associated with charge–discharge process. Alternatively, the incompressible volumetric changes in the hydride bed during sorption can also result in actuation. However the studies reported on this type of actuators are rare and mostly deal with bimorph actuators. The present study investigates the effect of soft silicone rubber composited metal hydride bed within a hollow stainless steel spring for its potential use as a self-sensing actuator element. LaNi5 is used as the metal hydride alloy. For an equivalent quantity of hydride by mass, the estimated actuation stroke and force for the composite bed actuator are better than their powder bed counterpart (12 mm and 100 N, respectively, in contrast to 5.84 mm and 60 N), due to improved heat transfer. Bed thickness, coil pitch and coil diameter are important geometric parameters which control the performance of the device. As previously reported, hydrogen supply pressure and heat transfer coefficient are found to be important operating parameters controlling the force –stroke characteristics of the actuating element. The simulation study has been executed using COMSOL Multiphysics™ commercial code.

Visualization study of improving anode water management by variable pressure hydrogen supply in proton exchange membrane fuel cell

To alleviate the prolonged closure of anodic outlet, which causes water to gradually accumulate in the porous layers that hinder hydrogen transfer in dead-ended anode mode. This study proposes an anode variable-pressure hydrogen supply strategy. The hydrogen supply pressure is suddenly reduced for a period before triggering purging, creating a pressure difference between the membrane assembly electrode and flow channels to induce water discharging into the flow channels, then directly purging out of the cell. Optical visualization is utilized to observe and analyze the effect of this strategy on water distribution and quantified through voltage, power, purging pressure change, and water coverage rate. Experiments indicate that the sudden pressure change in the variable pressure hydrogen supply mode effectively promotes water discharge from the porous layers, provides higher water coverage within the entire flow field, and promotes the fusion of neighboring droplets to form larger ones for better water management. Compared to normal mode, the proposed strategy achieves 3.4% performance improvement at 0.32A/cm2. Furthermore, a higher abrupt pressure difference favors porous layers drainage, but the optimal low-pressure duration requires a trade-off between drainage facilitating hydrogen transport and recovery of the membrane water content.

Design and optimization of metal hydride reactor with phase change material using fin factor for hydrogen storage

The solid-state hydrogen storage in metal hydride (MH) is safer and energy efficient than the gaseous and liquid storage methods. The absorption of hydrogen in MH is highly exothermic. Hence, a good heat management system is required to increase the charging rate. The phase change material (PCM) can be integrated into the reactor to reuse the absorption heat for hydrogen desorption. The present numerical study models the concentric cylindrical reactor with magnesium (Mg) as MH surrounded by sodium nitrate (NaNO3) as PCM using COMSOL Multiphysics v6.1. The effect of buoyancy inside the PCM domain is investigated. An iterative approach is used to determine the required amount of PCM. Copper fins are added inside both MH and PCM. The effect of the number of fins, corresponding fin thickness and pitch on hydrogen absorption are determined to optimize the MH reactor. The outcomes reveal that the hydrogen absorption rate increases with fin numbers. The reactor with 10 and 30 fins takes 86.5 and 97.3 % less time than without fins for 90 % hydrogen absorption, respectively. The novel approach is proposed to estimate the fin efficiency (ηf) using temperature profiles of MH and fin during prevailing unsteady heat and mass transfer. The fin factor (Ff) is presented using the ηf and mass of MH. The performance evaluation criterion (PEC) is discussed based on hydrogen absorption relative to the system's weight. Further, the effect of operating parameters like hydrogen supply pressure and the initial temperature is studied on the reactor performance.

Storage performance of a novel array metal hydride hydrogen storage reactor based on PCM thermal management

Metal hydrides (MH) are an attractive option for solid hydrogen storage with the large thermal effects of their hydrogen absorption and desorption processes when used in reactors. Phase-change materials (PCM) have been used as thermal management media in the MH reactor. To further improve the performance of the reactor, this study proposed a novel PCM-based MH reactor with array layouts, aiming to construct a heat transfer interface with a high specific surface area. A mathematical model was constructed to elucidate the phenomenon of heat transmission and absorption reaction. It was found that an increase in the number of array units significantly increased the heat transfer area but had a limited impact on enhancing the absorption rate and heat transfer. Nevertheless, the array reactor with seven units had a significant 1.0 times increase in the absorption rate compared to the traditional reactor with only one array unit. Furthermore, the enhancement of thermal conductivity in MH/PCM and the elevation of hydrogen supply pressure have the potential to accelerate the reaction rate and heat transfer during absorption. The enhanced absorption pressure not only enhances the driving force of the reaction directly but also amplifies the temperature difference in heat transfer between PCM and MH. Consequently, this leads to a further improvement in heat transfer and reaction efficiency.

Experimental investigation, development of machine learning model and optimization studies of a metal hydride reactor with embedded helical cooling tube

Metal hydride hydrogen storage systems are gaining popularity due to their advantages and suitability for various applications in variety of fields. In this study, a metal hydride reactor using LaNi5 as metal hydride and using water as heat transfer fluid flowing through embedded helical tube was fabricated and experimentally studied. The aim of this study is to experimentally investigate the effect of internal heat transfer arrangement on the absorption and desorption of hydrogen in a metal hydride system. The effect of mass flow rate and temperature of heat transfer fluid, effect of hydrogen supply pressure on the rate of hydrogen absorption and desorption was investigated. It was found that the increase in the hydrogen supply pressure, increase in mass flow rate and decrease in the temperature of heat transfer fluid, results in faster hydrogen absorption rate. Similarly, the increase in mass flow rate and the temperature of heat transfer fluid results in faster hydrogen desorption rate. It was also found out that maximum hydrogen absorbed inside metal hydride reactor was around 34.5 g which corresponds to a gravimetric capacity of 1.34 wt%. Further based on the experimental data various machine learning models were developed and tested and then these models were used for performance prediction. It was found that tree-based regression machine learning models are better compared to other models. Such models can thus be used for prediction of rate of hydrogen absorbed or desorbed and metal hydride bed temperature for different parametric values without doing detailed experimental and numerical trial. Finally, the brute force approach is used to optimize the system for three different applications. The optimization techniques help to fix the value of parameters for particular application and hence save multiple experimental run of absorption and desorption. This is a novel work in the field of using machine learning for modelling and optimizing the metal hydride-based reactor. Use of such tools can save lot of computational time, efforts and experimental resources.

A dynamic model for predicting the absorption and desorption behaviors of metal hydride systems and its implementation for screening of alloys for metal hydride hydrogen compressor

The goal of the current study is to develop a dynamic model for forecasting the absorption and desorption behavior of metal hydride hydrogen system. The accuracy of the developed dynamic model is verified with the actual model. The effect of reactor diameter (10–25 mm), hydrogen supply pressure (5–20 bar) and desorption temperature (40–70 °C) on the accuracy of the temperature profile predicted by the dynamic model as compared to the actual model is investigated. The results showed that the percentage deviation of the dynamic model with actual model increase with the reactor diameter. The dynamic model predicted the average bed temperature during absorption with a maximum deviation of 4.32% (14 K) for a reactor of 25 mm diameter compared to the actual model. A maximum deviation of only 2.11% (6.32 K) was observed for the same reactor during desorption at 323 K. Further, the percentage deviation increases with the supply pressure and desorption temperature. Overall, it is observed that the slower the absorption/desorption, the better is the prediction accuracy of the dynamic model. On the other hand, the dynamic model is over 300 times faster than the actual, which saves computational time and cost. Furthermore, the dynamic model is extended for studying the coupled reactor system of a dual-stage metal hydride hydrogen compressor. Four alloy pairs are compared in terms of compression ratio, the amount of energy lost due to hysteresis, average hydrogen discharge rate, and isentropic efficiency. The comparison results suggested that an appropriate combination of AB5-AB2 type alloy is suitable for higher delivery plateau pressure, lower energy loss due to hysteresis, and a reasonable compression ratio.

Influence of measurement parameters on hydrogen absorption properties of hydrogen storage alloys

ABSTRACT To predict real-time performance of metal hydride-based systems, La0.9Ce0.1Ni5 and LaNi4.7Al0.3 alloys are opted to investigate the influence of operating temperature and supply pressure on absorption kinetics. For the same, the pressure ratio is varied from 1.5 to 4 by keeping the temperature constant. Later, the operating temperature is varied (20–80°C) for the above range of pressure ratio. The study revealed that the absorption kinetics of metal hydrides is substantially influenced by operating temperature and supply pressure. It is observed that with an increase in pressure ratio (1.5, 2, 2.5, 3, and 3.5), the hydrogen supply pressure increases (9.75, 13, 16.25, 19.5, and 22.75), which creates high driving potential consequently results in faster reaction rates. However, increase in operating temperature (20°C and 40°C) at constant supply pressure (25 bar) results in slower reaction rates due to decrease in driving potential because the equilibrium pressure of La0.9Ce0.1Ni5 is higher at high temperature. The similar effect is obtained for LaNi4.7Al0.3. The experimental measurements are carried out using an in-house Sievert’s apparatus and are compared with numerical results obtained through a mathematical model that results in good agreement.

Thermal performance enhancement of metal hydride reactor for hydrogen storage with graphene oxide nanofluid: Model prediction with machine learning

Some metals and metal alloys can store gaseous hydrogen, making the storage of hydrogen in metal hydrides (MHs) possible. For the MH reactor to store hydrogen at a higher rate, improved heat transfer is required. The 2-D material graphene oxide (GO) attracted researchers’ attention due to its excellent thermal properties. The present work aims to improve heat transfer and hydrogen storage rate of the LaNi5 MH reactor. A 2-D axis-symmetric numerical model of the reactor is formed and simulated using COMSOL Multiphysics 5.6 software. Water and its based nanofluids (NFs), namely, GO, GO-SiO2 (50:50), GO-TiO2 (50:50), and Al2O3 are employed as heat transfer fluids (HTFs). The effect of inlet temperature and flow velocity of the HTF; and hydrogen supply pressure on the reactor performance is examined. The findings demonstrate that the storage rate is greatly improved by lowering the HTF inlet temperature; and increasing its inlet velocity and hydrogen supply pressure. In comparison to water and all other NFs, the GO NF with 1 vol% demonstrated comparatively better heat transfer. It reduces the duration by 61.7% of that of water to attain 90% hydrogen storage capacity at similar conditions. The data acquired in the numerical investigations were used to build a prediction metamodel using the evolutionary machine learning (ML) technique of gene expression programming (GEP).

Effect of fuel injection timing on performance and emissions with a dedicated direct injector in a hydrogen engine

In this study, hydrogen fuel was injected directly into a cylinder using a prototype of a dedicated hydrogen direct injector (HDI). The effects of fuel injection timing and amount of hydrogen fuel injected on engine output performance and emissions (e.g., nitrogen oxides and carbon dioxide) were investigated by varying the fuel injection timing from before top dead center (BTDC) 190 crank angle degree (CAD) toward BTDC 60 CAD. Strategies for maximizing the engine’s output performance when an after-treatment system for nitrogen oxide removal catalysts is not used were assessed. When using the HDI, a torque improvement result (up to 35.9%) can be obtained even under the condition that the hydrogen supply pressure was half as low as compared to the case of using a gasoline direct injector for hydrogen fuel. Under the condition of retarded fuel injection timing, a locally rich mixture is formed to increase the emission of nitrogen oxides at a level of 50 ppm or higher. The engine oil is burned to affect the emission of carbon dioxide (CO2), which is proportional to the load.

Performance optimization of metal hydride hydrogen storage reactors based on PCM thermal management

Metal hydrides (MH) are considered promising hydrogen storage materials. In applications, the heat transfer characteristics of MH hydrogen storage reactors are closely related to their storage performance. Phase change materials (PCM) were proven to integrate with MH reactors for effective thermal management. Nevertheless, the PCM based MH reactors (MH-PCM reactors) still need to overcome the heat transfer resistance and the loss of volumetric hydrogen storage capacity caused by the PCM volume proportion. The present work established a mathematical model to describe the transfer and reaction process in the MH-PCM reactor. Various parameters were discussed in the current work. It was found that the increased PCM's amount and latent heat have a restricted effect on the enhancement of heat transfer and absorption reaction rate. The higher PCM's thermal conductivity and hydrogen supply pressure effectively enhanced the heat transfer and reaction rate. Furthermore, the increased absorption pressure can improve PCM's sensible heat storage capacity, which provides a new approach for optimizing PCM consumption. Finally, the quantitative relationship among the volumetric hydrogen storage capacity, the volume fraction and thermophysical properties of PCM, and the absorption pressure were established by systematic analysis, which provides an essential theoretical basis for the optimization of MH-PCM reactors.

Hydrogen refueling stations and fuel cell buses four year operational analysis under real-world conditions

Worldwide about 550 hydrogen refueling stations (HRS) were in operation in 2021, of which 38% were in Europe. With their number expected to grow even further, the collection and investigation of real-world station operative data are fundamental to tracking their activity in terms of safety issues, performances, maintenance, reliability, and energy use. This paper analyses the parameters that characterize the refueling of 350 bar fuel cell buses (FCB) in five HRS within the 3Emotion project. The HRS are characterized by different refueling capacities, hydrogen supply schemes, storage volumes and pressures, and operational strategies. The FCB operate over various duty cycles circulating on urban and extra-urban routes. From data logs provided by the operators, a dataset of four years of operation has been created. The results show a similar hydrogen amount per fill distribution but quite different refueling times among the stations. The average daily mass per bus and refueling time are around 14.62 kg and 10.28 min. About 50% of the total amount of hydrogen is dispensed overnight, and the refueling events per bus are typically every 24 h. On average, the buses' time spent in service is 10 h per day. The hydrogen consumption is approximately 7 kg/100 km, a rather effective result reached by the technology. The station utilization is below 30% for all sites, the buses availability hardly exceeds 80%.

Performance tests on embedded cooling tube type metal hydride reactor for heating and cooling applications

• Heating and cooling traits of two AB 5 -type metal hydride alloys were investigated. • Heating performances of the alloys were found to be superior compared to cooling. • Peak heating rate of 3.5 kW was accomplished, producing 514 kJ heat within 361 s. • A decentralized heating cum H 2 storage system was suggested based on test results. The present work reports the heating and cooling characteristics of two AB 5 type metal hydride (MH) alloys commercially labelled as A3® and LCC1®. A cylindrical MH reactor configuration comprising 48 Embedded Cooling Tubes (ECT) in a circular pattern and an outer jacket was considered to accomplish the set objectives. Two identical reactors were each filled with 3.4 kg of one of the alloys. The reactor configuration allows MH alloy to be filled in the shell space while the heat transfer fluid (HTF) could flow through the tubes and the outer jacket. A set of parametric investigations was conducted on the aforementioned alloys by varying the operational parameters. During the absorption set of the parametric study, hydrogen supply pressure was varied from 10 bar to 30 bar, and HTF temperature was varied from 15 °C to 35 °C, while during the desorption study, HTF temperature was varied from 5 °C to 25 °C. At the absorption condition of 30 bar and 25 °C, the alloys A3® and LCC1® attained absorption capacity of 1.24 wt.% and 1.38 wt.%, respectively. At this condition, LCC1® was able to generate 514.5 kJ cumulative heat output in 361 s, yielding a maximum heating rate of 3.57 kW. The parametric study revealed that the absorption behaviour of A3® was more sensitive towards changes in supply pressure as well as HTF temperature compared to LCC1®. Compared to heating performance, the cooling performance of both the alloys was lower. Based on the outcomes of the experimental study, it was suggested to utilize LCC1® for decentralized hydrogen storage cum heating applications in the temperature range of 15–35 °C.

Bio-inspired leaf-vein type fins for performance enhancement of metal hydride reactors

Hydrogenation of metals is an exothermic and reversible process. Thus, metal hydride reactors/devices become essentially heat-driven. Excellent heat control in the MH reactor is required to develop metal hydride devices such as H2 storage systems successfully. Few attempts at nature-inspired designs have proven to have good heat transfer capabilities. Based on this idea, the present study investigates novel bio-inspired leaf-vein type fins for the metal hydride reactor. Two reactor designs are proposed for heat transfer fluid flow, namely (i) central straight tube and (ii) narrow trapezoidal channels with 10 kg of LaNi5 as a sample alloy. Compared to longitudinal finned single tube reactors (LFSTR), these designs provided better heat transmission and temperature uniformity. For LFSTR, Case-1, and Case-2, 90% storage capacity was reached in 210, 145, and 80 s. Different fin configurations, such as parallel, inclined fins, and fins of different thicknesses, are investigated further in the design with narrow trapezoidal channels. The inclined fin configuration shows better performance, and it is further optimized by varying the inclination angle from 3 to 9° and the fin number from 2 to 4. The optimized design with a 7° inclination angle and four fins required 57 s to attain 90% storage capacity and reduced absorption time by 73% compared to LFSTR. The influence of operating parameters such as hydrogen supply pressure, inlet temperature, and velocity of the heat transfer fluid on the performance is evaluated for the optimized design.

Experiments on a novel metal hydride cartridge for hydrogen storage and low temperature thermal storage

Even though metal hydrides have been mainly studied for hydrogen storage, their applications can be extended to thermal energy storage by utilizing the exothermic and endothermic reactions during the hydride formation and decomposition processes, respectively. In this paper, a low temperature hydride, La0.75Ce0.25Ni5 is experimentally investigated for hydrogen storage and thermal energy storage applications. Heat and mass transfer characteristics of a novel scalable cartridge type reactor is studied at various heat transfer fluid temperatures and hydrogen supply pressures. Maximum hydrogen storage capacity of 1.38 wt% and a gravimetric thermal energy storage capacity of 127.01 kJ.kgMH-1 at about 70% efficiency were achieved. The energy storage capacity achieved during experiments is compared with the theoretically possible output by defining a performance index, namely, the energy storage effectiveness, and its maximum value was found to be 0.67 at 20 °C and 20 bar.

Four years of operational data for five hydrogen refueling stations

Worldwide about 550 hydrogen refueling stations (HRS) were in operation in 2021, of which 38%. were in Europe. With their number expected to grow even further, the collection and investigation of real-world station operative data are fundamental to tracking their activity in terms of safety issues, performances, costs, maintenance, reliability, and energy use. This paper shows and analyses the parameters that characterize the refueling of 350 bar fuel cell buses in four HRS within the 3Emotion project. The HRS are characterized by different refueling capacities, hydrogen supply schemes, storage volumes and pressures, and operational strategies. From data logs provided by the operators, a dataset of three years of operation has been created. In particular total hydrogen quantity, the fill amount dispensed to each bus, the refueling duration, the average mass flow rate, the number of refueling events and the daily number of refills, the daily profile, the utilization factor, and the availability are investigated. The results show similar hydrogen amount per fill distribution, but quite different refueling times among the stations. The average daily mass per bus is around 12.95 kg, the most frequent value 15 kg, the standard deviation 7.46. About 50% of the total amount of hydrogen is dispensed overnight and the refueling events per bus are typically every 24 hours. Finally, the station utilization is below 30% for all sites.

Experimental analysis of an ejector for anode recirculation in a 10 kW polymer electrolyte membrane fuel cell system

For analyzing ejector's performance in the system, an ejector for a 10 kW polymer electrolyte membrane fuel cell (PEMFC) system was first designed, manufactured, and a 10 kW PEMFC system bench was built up. A proportional valve and PI pressure feedback control method were adopted to control the hydrogen supply and anode inlet pressure. During the test, performances between dead-ended anode (DEA) mode and ejector mode were compared. Ejector's performances in the system, i.e., volume flow recirculated ratio, difference pressure, dynamic responses of primary pressure, anode inlet pressure, and recirculated gas flow rate during the purge process and current variation condition, were investigated. The results show that pressure adjustment is accurate, continuous, and fast using the proportional valve and PI pressure feedback control method. The hydrogen consumption rate in the ejector mode can reduce from 5% to 10% compared with the rate in the DEA mode except for the stack current 5 A and 10 A conditions. For better water removal out of the anode channel in ejector mode, the maximum stack power increases from 5.11 kW (DEA mode) to 9.56 kW (ejector mode). Anode pressure surge caused by the purge valve switching enhances the ejector's recirculated performance significantly.

Experimental study on temperature variation of metal hydride reactor incorporating helically coiled heat exchanger during absorption

Incorporating the helically coiled heat exchanger (HCHE) into the metal hydride (MH) reactors is an effective way to improve the hydrogen absorption rate. In the present study, an MH reactor incorporating a HCHE was built to investigate the influences of various operating parameters on the bed temperature and the heat transfer fluid outlet temperature at the hydrogen supply pressure (ps) of 0.8–1.2 MPa, the fluid inlet temperature (Tin) of 20–40 °C, and the fluid flow rate (qf) of 10–50 L h−1. The experimental results show that the increase in the ps and qf can improve the heat transfer performance and accelerate the hydrogen absorption process. Nevertheless, increasing ps makes the temporal variations of the bed temperature and fluid outlet temperature more unevenly, which limits the utilization for the heating system. Furthermore, the recommended fluid velocity (1.0–3.0 m s−1) inside heat exchanger tubes is not suitable for the MH reactor design. Compared with the hydrogen supply at constant pressure, the highest values of the MH bed temperature and the fluid outlet temperature rise are lower at constant flow rate of hydrogen. In addition, the hydrogen absorption process can be controlled by changing the hydrogen flow rate.