Liquid Hydrogen Storage System Research Articles

Theoretical analysis of entropy generation in multilayer insulations: A case study of performance optimization of variable density multilayer insulations for liquid hydrogen storage systems

Liquid hydrogen (LH2) is a promising and economical clean energy for achieving global carbon neutrality. Multi-layer insulation (MLI) with high performance is essential for the safe storage and operation of LH2. To perform a better optimization of MLI, the second law of thermodynamics becomes a complement to the first law of thermodynamics. However, very few studies have carried out the optimization of MLI performance through the second law of thermodynamics. For the sake of achieving more efficient optimization of MLI as well as revealing the fundamental indicators limiting the performance of MLI, this paper analyzes the characteristics of entropy generation produced by the solid heat conduction, thermal radiation, and residual gas conduction distributed in the MLI schemes by a validated layer-by-layer model.For a 40-layer MLI arranged with a constant layer density of 20 layers/cm, the first 15 layers near the cold boundary occupy more than 98% of the total entropy generation, providing an effective range of layers for thermodynamic optimization. Besides, an optimization of variable-density MLI (VDMLI) separated into two segments based on the entropy generation minimization is conducted. The optimal VDMLI has substantially lowered the entropy generation from the solid heat conduction but at the cost of increasing the entropy generation from radiation and residual gas conduction. This study provides a reliable optimization method of MLI, which allows the safe storage of clean energy with a low boiling temperature.

Rapid prediction of water hammer characteristics in liquid hydrogen storage and transportation systems: A theoretical model

A renewable energy liquid hydrogen storage and transportation system is a very complex system, so water hammering due to valve closure cannot be ignored. A theoretical model for the rapid prediction of the water hammer effect in liquid hydrogen pipeline valves was developed in this work. The impact of valve closure characteristics and subcooling on the peak pressure water hammer was analyzed. The results indicate that as the subcooling temperature of liquid hydrogen decreases, the density of subcooled liquid hydrogen increases, leading to larger peak pressures in the water hammer transient. At subcooling temperatures of 14, 16, 18, and 20 K, the maximum instantaneous pressures for the water hammer fluctuation are 51563.02, 50846.76, 50082.40, and 48510.70 Pa, respectively. Under identical boundary conditions, the density of subcooled liquid hydrogen emerges as the primary factor influencing the peak pressure of water hammer. The theoretical model exhibits a significant advantage in terms of computational time cost, saving approximately 9.99 h. However, the accuracy of the theoretical model is slightly inferior to that of the CFD model. The results of the study are expected to provide a technical basis for the design of refueling systems for storage and transportation, as well as densification technology of supercooled renewable liquid hydrogen and safety protection.

Heterogeneous Oxidase-Type Catalysis for H2 Generation at Low Temperatures.

The long-term objective in the field of heterogeneous catalysis is to develop an enzyme-like catalytic pathway that can achieve exceptional catalytic performance even at low temperatures. Herein, we have demonstrated a heterogeneous oxidase-type catalysis on the ZnO-supported Ru clusters (Ru/ZnO) for efficient H2 generation from an aqueous solution of formaldehyde (HCHO) at low temperatures. Due to its unique reaction pathway, the Ru/ZnO catalysts exhibited a temperature-insensitive activity for H2 generation at the temperature of 15 to 45 °C. Remarkably, even at a low temperature of 5 °C, the Ru/ZnO catalysts still enabled an H2 generation rate of 13.8 mmol gcat-1 h-1 with a turnover frequency (TOF) of 1678 h-1. Additionally, instead of producing a CO2/CO molecule, the HCHO molecule underwent a transformation into formic acid and/or formate as the byproduct. This finding presents a novel class of heterogeneous catalysts to expand the potential application scenarios of liquid hydrogen storage and transportation systems.

Liquid hydrogen storage and transfer-control system for integrated zero emission aviation (IZEA)

The growth in the aviation sector has highlighted the need to decrease carbon emissions, a significant factor in climate change. Hydrogen is a potential alternative clean fuel due to its high energy density. As a collaborative effort in developing integrated zero emission aviation (IZEA, a NASA ULI), we present the design concept for a liquid hydrogen storage system for short-range aircraft with a gravimetric index greater than 0.6. Our design leverages the cryogenic cooling power of liquid hydrogen to support the temperature and heat loads of various power system components, such as the high-temperature superconducting (HTS) generator, HTS motor, DC power distribution cable network, and power electronic converters. By controlling the pressure in the storage tank, we demonstrate that it is feasible to deliver the desired mass flow rate of hydrogen while effectively cooling the power system components using practical heat exchangers. Also, since heat exchangers are an integral part of our hydrogen storage and flow system, their design also impacts the overall system storage density. The entire system is designed considering the space and weight factors of an aircraft. This work represents a significant advancement towards developing the complete IZEA thermal management system for a given airplane and flight profile.

TRANSIENT ANALYSIS OF LIQUID-HYDROGEN TRANSFER IN CRYOGENIC STORAGE TANKS

Efficient transfer of liquid hydrogen is critical for a myriad of processes in terrestrial and extraterrestrial applications. The objective of this study is to model and quantify the amount of liquid parahydrogen vaporized during a discharging/charging process in a cryogenic storage system. The effects that are included include geometrical effects (storage tank volume), two-phase compressible flow, choking/unchoking, and wall-fluid heat transfer. A brief description of other physical boil-off mechanisms is also presented. This study provides a foundation for applicationspecific optimization. The storage system studied comprises two interconnected tanks whose transfer line has a variation in the flow area. This simulates current liquid-hydrogen storage and transportation systems. The model tracks the temperature- and pressure-time histories of liquid hydrogen as it flows between storage tanks, in both the choked and unchoked flow regimes. The transfer of liquid is induced solely by the pressure differential that exists between the two storage tanks. An iterative technique helps account for choking, which is likely to exist at the throat in two-phase flow. Cases of zero and infinite tank-wall thermal mass are also discussed. By analyzing the behavior of fundamental variables during the transient transfer of liquid hydrogen, boil-off losses may be minimized if the variables with the greatest effect on boil-off losses are controlled.

Heat Flow Characteristics at the Cryogenic Temperature According to the Distance of Stem in the Liquid Hydrogen Storage System for Hydrogen Electric Vehicles

Heat Flow Characteristics at the Cryogenic Temperature According to the Distance of Stem in the Liquid Hydrogen Storage System for Hydrogen Electric Vehicles

Effects of the wall temperature on the boiling process and the molecular dynamics behavior of the liquid hydrogen on a flat aluminum wall

Understanding the nucleation mechanism and boiling heat transfer characteristics of liquid hydrogen is a key issue in the development of liquid hydrogen storage systems. However, the current methods of experimental and mesoscopic or macroscopic scale continuous flow simulations suffer from the problems of large study scales and undetermined initial boundary conditions. The purpose of this study is to reveal the bubble nucleation mechanism and bubble development process of liquid hydrogen on the surface of heating plate at the molecular scale, and to investigate the effect of different heating plate temperature on bubble growth, during thin film boiling. In this research, molecular dynamics simulation is used to combine molecular position distribution with energy analysis and explain the molecular behavior. The effect of heating temperature on different phase transition stages of liquid hydrogen is also investigated by varying the heating surface temperature. In this study, the bubble nucleation, bubble development and merging of liquid hydrogen on the heating surface were successfully observed. It is shown that increasing the heating temperature has a small effect on the bubble growth rate and liquid layer thickness in the nucleation boiling stage, and mainly affects the gas film growth rate in the film boiling stage. The bubbles are extremely unstable at the initial stage of generation. Within 1 fs of the first appearance of bubbles, which are associated with random micro-pits caused by thermal motion of solid atoms, bubbles move on the surface of the heating plate. This study found a phenomenon that bubbles firstly generated and then disappeared. This paper provides a new idea for the nucleation mechanism and boiling heat transfer study of liquid hydrogen. Moreover, it provides a solution to the problems of liquid hydrogen phase change research.

A quasi-2D thermodynamic model for performance analysis and optimization of liquid hydrogen storage system with multilayer insulation and vapor-cooled shield

Liquid hydrogen (LH2) holds great potential in both aerospace and civil markets due to its high energy density. However, on account of the low boiling point and latent heat of vaporization of LH2, the high performance insulation storage system is the key to its efficient storage. One of the most efficient insulation methods for a LH2 storage system is considered to be Variable Density Multilayer Insulation (VDMLI) coupled with Vapor-Cooled Shield (VCS). This study establishes a quasi-two-dimensional (quasi-2D) thermodynamic model of liquid hydrogen storage system with VDMLI and VCS. The quasi-2D model incorporates the temperature gradient of VCS and its impact on VDMLI. The model can reveal the two-dimensional temperature and heat distribution in insulation systems, predict heat leakage and evaporation rate, and can be utilized for optimizing the design of the VCS structure. Using a NASA's tank as an example, the analysis conducted with the model indicates that the presence of VCS reduces the average temperature gradient of the inner VDMLI. The upper half of the tank exhibits a significantly smaller temperature gradient compared to the lower half, resulting in lower heat leakage. This effect becomes more pronounced as the VCS moves outward of the tank. Additionally, the VCS absorbs more heat in the inlet section than that in the outlet section, and this disparity becomes increasingly significant as the VCS moves outward of the tank. The model can also be employed to optimize the position of the VCS, resulting in a 69.73 % reduction in daily evaporation rate compared to NASA's original design. Lastly, a graphical method for the quick design of VCS structure is proposed which is based on calculated data for daily evaporation rate and apparent thermal conductivity. This method enables the retrieval of the corresponding apparent thermal conductivity based on the desired evaporation rate, facilitates the rapid determination of the range of VCS position, and allows for the quick prediction of the evaporation rate based on the VCS position. In conclusion, this research presents a new approach for the performance analysis and optimization design of liquid hydrogen storage system with VDMLI and VCS.

Liquid hydrogen storage design trades for a short-range aircraft concept

Preliminary design trades for the liquid hydrogen storage system of a short-range aircraft are presented. Two promising insulation methods, namely rigid foam and multilayer insulation, are identified as main design drivers. In addition, the maximal pressure and the shape of the hydrogen storage tank influence the aircraft performance and the insulation efficiency. In this study, the hydrogen storage tanks are integrated in wing pods. The main effects driven by the design parameters are addressed using conceptual and preliminary methods: models are carried out for the storage mass, additional drag, propeller efficiency loss and the dynamical thermodynamic behavior of the liquid hydrogen storage. These effects are coupled making an integrated design method necessary. For the sizing of the liquid hydrogen storage, a multidisciplinary workflow is set up including the aircraft sensitivities on the design mission block fuel. The trade-off study reveals the opposing trend between insulation efficiency and aircraft performance. For the insulation architecture based on rigid foam, the penalties implied by the storage tank on aircraft level and the penalties due to vented hydrogen can be balanced and result in minimal block fuel for the design mission. The application of multilayer insulation avoids venting during the design mission, but has an increased penalty on the aircraft performance compared to rigid foam insulation. Besides the criterion of minimal block fuel, the dormancy time is compared, indicating the thermal efficiency. Applying multilayer insulation, the dormancy time can be increased significantly calling for a discussion of operational requirements for hydrogen-powered aircraft.

Transient flow dynamics behaviors during quick shut-off of ball valves in liquid hydrogen pipelines and storage systems

The cryogenic nature of liquid hydrogen can lead to brittleness in materials, posing a significant risk of severe safety incidents due to liquid shock. In this study, the compressibility of liquid hydrogen and the rapid closing of the valve are described by user defined function (UDF) using Fluent software, and the reliability of the calculation simulation is verified based on the water hammer experiment and theoretical model. The results show that the rapid closure of a valve causes liquid hydrogen to generate a significant pressure change, leading to a swift drop of flow velocity in the liquid hydrogen pipeline. The pressure fluctuation amplitude near the valve is greater than the pressure fluctuation amplitude away from the valve, and the pattern for velocity is reversed. For valve closing time of tvalve is 0.84, 1.68, and 3.36 times of Tp, the maximum transient flow pressure in the pipe is 60.96 kPa, 48.49 kPa, and 39.06 kPa, respectively. The transient flow pressure is 2.4, 1.9, and 1.5 times for the inlet pressure at valve closing times of 0.01, 0.02, and 0.04 s, suggesting that the quicker the valve closes, the higher the maximum transient pressure in tubes. Furthermore, a new pressure fluctuation coefficient is introduced to describe the transient flow characteristics of the liquid hydrogen in the pipelines. The valve closing time is halved, and the pressure fluctuation coefficient doubles. The research results are expected to provide a technical basis for liquid hydrogen pipelines' design and vibration reduction.

Experimental and dynamic simulation study of the Joule-Thomson cryocooler working at liquid hydrogen temperature

With advantages of long-life time, low level vibration and continuous refrigeration, precooling Joule-Thomson cryocooler (PJTC) working at liquid hydrogen temperature has the potential to be applied to liquid hydrogen storage system in space. For the large-cooling-power PJTC working at liquid hydrogen temperature, its dynamic response characteristic to heat load has a great importance on liquid hydrogen storage system, especially in aerospace applications. In order to study dynamic characteristics of PJTC working at liquid hydrogen temperature, an experimental setup for an open-cycle PJTC is built and its dynamic model is established by MATLAB software. Cool-down process and temperature variation characteristic with a heat load of 10.19 W are simulated and verified with experimental results. Meanwhile, the effect of precooling power on the performance of JT cryocooler is analyzed. It is found that if the precooling power is lower than 50% of the original precooling power, the recovery time of JT cryocooler will increase significantly.

Demonstration and thermal equilibrium analysis of a 10 kJ capacity energy storage coil made of MgB2 with liquid hydrogen indirect cooling

We have demonstrated an advanced superconducting power conditioning system, in which a superconducting magnetic energy storage (SMES) device, a generator based on a fuel cell (FC), and an electrolyzer are used to compensate for electricity fluctuations over a wide frequency range, combined with a liquid hydrogen storage system to both cool the SMES and provide pure hydrogen gas to the FC and other gas-dependent systems. To manufacture the coils for the SMES, we used MgB2, whose critical temperature is below the boiling temperature of hydrogen. We developed a 10 kJ SMES coil system indirectly cooled by liquid hydrogen using thermosyphon passive heat exchange to isolate the flammable hydrogen from the electrical components. We performed a successful demonstration of this system for both DC and AC currents ramped at different rates. In the present study, we use computer simulations involving heat balance equations to evaluate the stability of the system. The results obtained are expected to lead to the design of future large-capacity energy storage systems, such as the MJ class, which offer comparable performance to conventional NbTi SMES devices.

Liquid hydrogen storage system for heavy duty trucks: Capacity, dormancy, refueling, and discharge

Continuing the previous work on configuration, performance, cost, and safety of liquid hydrogen (LH2) storage for Class 8 heavy-duty trucks, we examine and demonstrate the feasibility of meeting the targets of 750 mile (1200 km) driving range, 65 kg H2 storage capacity, 8–10 kg/min refueling rate, 4.6 g H2/s peak discharge rate, 1–3 day dormancy, 5000 refueling cycles, 15% gravimetric capacity, 35 g/L volumetric capacity, and $8/kWh total system cost. A thermodynamic model is developed to determine the useable H2 density considering ullage and LH2 heel subject to heat transfer through the multilayer vacuum insulation and dormancy in the limits of “full” and “empty” fuel tanks. Dynamic simulations are conducted to determine the fraction of gaseous H2 returned to the station Dewar during refueling and heat input by H2 recirculation through an in-tank heat exchanger during discharge. The system gravimetric and volumetric capacities are affected by availability of on-board LH2 pump, discharge pressure, and dormancy. Compared to compressed H2 at 350 and 700 bar in carbon fiber wound Type 4 tanks, LH2 storage in double walled, vacuum insulated, low-pressure Type 1 tanks for heavy duty trucks shows advantages of 34–54% higher useable H2 storage density, 59–68% higher gravimetric capacity, 25–48% higher volumetric capacity, and 36–41% lower cost.

Effects of longitudinal excitation on liquid hydrogen sloshing in spacecraft storage tanks under microgravity conditions

Based on the real physical model and operating environment of the spacecraft tank, the numerical model of the tank is established and the sloshing behavior of liquid hydrogen in the tank under different longitudinal excitations is studied in this work. The Realizable k- ε model is used to predict the fluid turbulence, and the mixture model is used to analyze the phase transitions and flows. The harmonic external excitation is loaded by the user-defined function (UDF). Based on the CFD sloshing model verified through comparison with experimental results, the influences of different longitudinal external excitation frequencies and amplitudes on the liquid hydrogen volume fraction in the tank are firstly analyzed. On this basis, including pressure and other physical quantities of the monitoring points and whole internal fluid domain during the sloshing simulation process are studied quantitatively. In addition, the relationship between the carrier amplitude of the sloshing curves and the external excitation amplitude is discussed. The simulation results show that in microgravity environment, compared with large amplitude excitation, high-frequency longitudinal harmonic excitation has a significant effect on the variation of physical parameters in the tank, which may become a negative factor for the safety of liquid hydrogen storage and supply systems. Meanwhile, the traditional baffle design has a limited influence on the liquid hydrogen motion under the high-frequency longitudinal excitation which may occur during the spacecraft changing load process. The results provide valuable information for the understanding of sloshing behavior and safety evaluation of the tank under longitudinal excitation.

Vehicle-mounted Dual Liquid Hydrogen Cylinders Parallel Balanced Transport Experimental and Simulation Research

For heavy vehicle liquid hydrogen storage and supply system, the use of double liquid hydrogen cylinders to increase the supply of liquid hydrogen. When two liquid hydrogen cylinders supply liquid hydrogen in parallel, the flow resistance of the gas and liquid channels of the liquid hydrogen cylinders is difficult to achieve complete consistency, which makes the flow of the two liquid hydrogen cylinders in the process of hydrogen supply different, resulting in inconsistent liquid levels in the two liquid hydrogen cylinders. For this reason, a parallel balanced transport technology scheme of two liquid hydrogen cylinders was proposed. Two liquid hydrogen cylinders with identical size were used to supply liquid hydrogen, and a gas-line connecting pipe was used in the gas path of the liquid hydrogen cylinder to achieve the same pressurization pressure of the two liquid hydrogen cylinders. A regulating valve was used to realize the consistent flow of liquid route at the outlet of liquid hydrogen cylinders. Then, the experimental system modified with real liquid hydrogen cylinder was tested with water medium, and the correctness of the simulation results was verified by the test results. Finally, the simulation results show that the proposed method can ensure that the level difference of liquid hydrogen cylinders meets the requirements in the process of parallel supply of liquid hydrogen.

Liquid hydrogen storage system for heavy duty trucks: Configuration, performance, cost, and safety

Liquid hydrogen storage system for heavy duty trucks: Configuration, performance, cost, and safety

Performance and Total Cost of Ownership of a Fuel Cell Hybrid Mining Truck

The main objective of this work was to investigate the potential of hydrogen and fuel cells replacing diesel and internal combustion engines in the ultraclass haul trucks deployed in the mining sector. Performance, range, durability, and cost are the main criteria considered for comparing the two fuels and engine options. Fuel cell system (FCS) performance is characterized in terms of heat rejection, efficiency, and fuel consumption for a hybrid platform equivalent to a 3500 hp diesel engine operating on a representative open pit mining duty cycle. A hybrid platform was chosen because the heat rejection, with a constrained radiator frontal area, limits the maximum fuel cell-rated power by about 50% compared to that of the diesel truck. The hybrid powertrain was 81–88% more efficient than the diesel powertrain on the truck duty cycle. A liquid hydrogen storage system is required for an equal range or time between refilling, but the packaging remains a challenge. Fuel cell and battery durability were evaluated for their performance degradation and lifetime. Achieving a fuel cell lifetime comparable to the time between major overhauls for diesel trucks necessitates the oversizing of the membrane-active area, catalyst overloading, and voltage clipping. For an equal lifetime, the battery must be oversized to control its depth of discharge and charge/discharge rates. A total cost of ownership (TCO) analysis considering the initial capital expenditures, as well as the lifetime cost of fuel, operation, and maintenance, indicates that fuel cells and hydrogen can compete with diesel. A breakeven fuel cost for TCO parity is obtained if H2 is available at USD 5.79–6.85/kg vs. diesel at USD 3.25/gal and the FCS-specific cost is USD 323/kWe relative to USD 250/kW for a diesel genset. Volume manufacturing is required for FCS cost reduction. High volume is possible through the standardization, modularity, and proliferation of class 8 long-haul truck systems across different heavy-duty applications.

Modeling and Analysis of the Flow Characteristics of Liquid Hydrogen in a Pipe Suffering from External Transient Impact

Pipes can be subjected to external transient impacts such as accidental collision, which affects the safe operation of storage and transportation systems for liquid hydrogen. Fluid–structure coupling calculation for a pipe under external transient impact is performed, and the flow characteristics of liquid hydrogen in the pipe are analyzed. The pipe deforms and vibrates when suffering from external transient impact. Liquid hydrogen pressure in a cross-section plane increases along the pipe deformation direction. Additionally, external transient impact enhances the disturbance of liquid hydrogen near the pipe wall. The increased flow resistance and the energy induced by the deformed pipe both affect the flow of liquid hydrogen, and contribute to the fluctuated characteristics of liquid pressure drop. In addition, the phase state of liquid hydrogen remains unchanged in the pipe, indicating that little of the induced energy is transformed into the internal energy of liquid hydrogen. The work provides theoretical guidance for the safe operation of liquid hydrogen storage and transportation systems.

Opportunities and data requirements for data-driven prognostics and health management in liquid hydrogen storage systems

During the past decade, Prognostics and Health Management (PHM) has become an important set of tools in various areas of industry and academic reliability engineering. PHM consists of a variety of mathematical and computational methods used to support data-driven decision-making to increase the safety, availability, and reliability of complex engineering systems. In particular, PHM can provide crucial insight into reliability and safety design improvements for developing technologies where historical performance and failure data are limited. This is the case of hydrogen fueling and storage technologies. This work presents a high-level approach for designing data-driven PHM applications for bulk liquid hydrogen (LH2) storage systems for hydrogen fueling stations. This paper addresses core aspects of the design, development, and implementation of data-driven PHM applications that can improve the reliability assessment of hydrogen components. The analysis focuses on the relationship between data availability and diagnostic/prognostic capabilities; potential challenges; and integration schemes for current risk mitigation measures. We identify potential condition-monitoring data sources for key components in an LH2 storage system, including storage tanks, piping, and pumps. We determine that the short-term goals for the implementation of data-driven models in PHM frameworks in hydrogen systems should focus on developing adequate data collection and analysis strategies, as well as exploring the effect on reliability, safety, and regulations for hydrogen systems.

High hydrogen release by cryo-adsorption and compression on porous materials

Although hydrogen is a promising energy carrier to replace fossil fuels and reduce CO 2 emissions, its low volumetric energy density remains a major drawback. Indeed, hydrogen storage is one of the main technical obstacles limiting the large-scale use of hydrogen in fuel cell vehicles (FCVs). To solve this problem, there are different technical approaches such as: (i) compression in gas cylinders, (ii) liquefaction in cryogenic tanks, (iii) cryo-compression; and (iii) absorption or adsorption into solids. Cryogenic adsorption pressure systems are a promising approach to hydrogen storage because they require less resistant materials than those needed for compression at 70 MPa at room temperature, and can avoid the gas loss associated with boiling in liquid hydrogen storage systems. In this manuscript, we have reviewed different solutions for hydrogen storage, with a particular focus on hydrogen adsorption at cryogenic temperatures and moderate pressures on high surface area porous materials, namely: activated carbons, hyper-crosslinked polymers and metal organic frameworks. In addition, we discuss the elements involved in the design of rapidly rechargeable, compact, lightweight and cost-effective hydrogen storage systems. We also provide not only hydrogen storage capacities but hydrogen release capacities considering hydrogen at 10 MPa a discharge at 0.5 MPa. • Hydrogen storage by compression, liquefaction and cryo-compression is reviewed. • Hydrogen storage enhancement by adsorption in cryo-compression systems is discussed. • Cryo-adsorption of hydrogen on high surface materials is thoroughly reviewed. • The pros and cons of high surface area polymers, carbons and MOFs are presented. • Data on useable hydrogen in cryo-adsorption systems are reported.