Liquid Hydrogen Systems Research Articles

Contact electrification characteristics of solid oxygen particle-laden flows in liquid hydrogen transportation

The issue of electrostatic safety in liquid hydrogen systems has garnered increasing attention, especially concerning the potential threat of electrostatic explosions due to the collision-electrification phenomenon of solid oxygen particles formed after air leakage in liquid hydrogen pipelines. To delve into the contact electrification characteristics of solid oxygen particle-laden flows in liquid hydrogen transportation, a mathematical model based on the computational fluid dynamics-discrete element method (CFD-DEM) two-phase flow dynamics has been developed. This model integrates the Hertz contact theory for describing particle collision processes and the condenser model for describing particle collision-electrification. The reliability of this model has been validated in existing literature through its ability to capture the flow characteristics of two-phase flow and the electrification characteristics of particle groups. Using density functional theory to compute the solid oxygen work function and considering the low-temperature properties of liquid hydrogen, a series of numerical studies on the flow sedimentation and electrification characteristics of solid oxygen particle-laden flows in liquid hydrogen pipelines have been conducted. The results indicate that particles carry negative charges after colliding with stainless steel pipe walls, with single charge exchange magnitudes of approximately 10−12C for particle-wall continuous collision processes and 10−14C for particle-particle collision processes, resulting in particle charge-to-mass ratios on the order of tens of μC/kg at the outlet interface. The impact of electrostatic forces on particle motion is significant and cannot be overlooked. Furthermore, the effects of velocity, particle diameter, and pipe diameter on particle charge characteristics have been thoroughly analyzed. At low flow velocities, severe particle settlement occurs, leading to increased collision frequency between particles and walls and significant charge accumulation. Increasing flow velocity can mitigate particle settlement and reduce charge levels. Changes in particle and pipe diameters have a minor impact on particle settlement but can increase single charge amounts with larger particle diameters and intensify particle charging with reduced pipe diameters due to shortened radial travel distances, leading to increased collision frequency. Our study meticulously illustrates the charge characteristics of individual particles and particle groups, providing a theoretical basis for assessing the electrostatic safety of liquid hydrogen transportation systems under extreme conditions.

Model Based Exploration of Physical Parameters for Liquid Hydrogen System Insulation Performance

Cryogenic Systems require a highly efficient insulation so as to limit the heat ingress and boil-off, which is generally achieved through the use of vacuum combined with an insulated media. The performance of Multi layer Insulation (MLI) will be investigated with detailed thermal models developed to account for all the heat transfer contributions, solid conduction, gaseous conduction and radiation. Results are presented for an usual cold vacuum pressure (CVP) corresponding to high vacuum (<10−6 torr) and compared with available experimental measurements for state of the art technologies. The nominal thermal performances are then evaluated for a cold temperature of 20K (representative of liquid hydrogen storage temperature), for a degraded CVP with hydrogen and nitrogen as residual gasses and for increased hot boundary temperatures. Other parameters are also discussed such as, the number of layers, material, layers density, venting options, assembly process and material optical properties. Finally, a sensitivity of the thermal performance is also presented with a pressure gradient through the insulation thickness, that could be induced by cryopumping, materials outgassing, pumping times or small leakages.

Simulation and analysis of fire and pressure reducing valve damage in on-board liquid hydrogen system of heavy-duty fuel cell trucks

Simulation and analysis of fire and pressure reducing valve damage in on-board liquid hydrogen system of heavy-duty fuel cell trucks

Modeling of solid-air multi-dendrite growth evolution driven by coupled thermal-solute using non-isothermal quantitative phase field method

The safety hazard posed by residual or infiltrated air condensing into external oxygen-rich solid-air (SA) particles in the liquid hydrogen container deserves attention. In this study, the patterns of morphological evolution, oxygen solute distribution, and growth rate of SA single- and multi-dendrite under various thermal environments are investigated using a non-isothermal quantitative phase field model for the first time. The lattice anisotropy problem of six-fold symmetric dendrites is effectively avoided. The results show that the Type II boundary condition is more suitable for the simulation of dendrite growth, which can avoid the influence of boundary conditions on dendrite growth. In addition, the suitability of the isotropic difference method for simulating the growth of SA multi-dendrites with six-fold symmetry is verified in this paper. The maximum values of solid fraction and oxygen solute concentration within the simulated domain are 0.62 and 0.435, respectively, for an initial subcooling degree of 4 K. The temperature distribution is significantly altered by the application of boundary heat flux and affects the growth pattern of SA dendrites. Compared to the scenario with no boundary heat flux, unilateral heat input and heat extraction decreased the solid fraction of SA dendrites by 31% and increased it by 43%, respectively, while the maximum concentration of oxygen solute was reduced to 144.8% and 97.3%, respectively. When boundary heat flux was applied to all quadrilateral boundaries, the solid fraction under heat extraction and heat input conditions is reduced by 82% and enhanced by 138%, respectively, compared to the scenario with no boundary heat flux. Additionally, the maximum concentration of oxygen solute is found to be 197.6% and 69.5% of that without boundary heat flux, respectively. This study improves the understanding of the evolution of solid-air dendrite growth and can provide theoretical guidance for the safe use of liquid hydrogen systems.

Numerical simulation of air solidification process in liquid hydrogen with LBM-CA coupled method

The solidification process of solid-air is a significant risk in liquid hydrogen system. To predict the solidification of air in liquid hydrogen, the coupled model of Lattice Boltzmann Method (LBM) and Cellular Automation (CA) has been proposed. Results shows that the local oxygen mass ratio can reach up to 30% at 0.1s when the air-proportioned nitrogen and oxygen mixture is solidified. The LBM-CA method is further used to study the effects of forced convection on the solid-air dendrite. It is shown that the upstream latent heat and the rejected solutes accumulate in the downstream with the flow field, leading to higher oxygen concentration in the downstream as the flow velocity increases. In addition, the solid-phase fraction of solid-air increases faster with the increasing flow velocity which indicates an increasing safety risk for the liquid hydrogen with solid-air system.

Investigation of boiling hydrogen heat transfer characteristics under low-pressure conditions

Understanding the heat transfer characteristics of boiling hydrogen is a critical issue in developing of liquid hydrogen system. However, there has been insufficient systematic research on boiling hydrogen flow characteristics. This report investigates the heat transfer characteristics of boiling hydrogen, following our previously reported gas-liquid mixing characteristics and flow regime transition characteristics. This study generated an arbitrary gas-liquid two-phase flow state in 15 mm tube by experimentally heating liquid hydrogen with an electric current. The experimental conditions were a pressure of 250 – 300 ▪, a mass flux of 50 – 110 ▪, and a heat flux of 0 – 12 ▪. Based on the experimentally obtained heat transfer coefficients, a heat transfer prediction model for boiling hydrogen was constructed, considering the change in the heat transfer process from liquid single-phase to saturated boiling. A one-dimensional flow simulator was also constructed that applies the proposed model and confirms that the model can be reduced the wall temperature error to about 1/10 against the conventional models.

Valve design considerations in liquid hydrogen systems to prevent failure

Hydrogen has potential as an alternative source of energy (energy carrier) because it can be converted, stored, and used efficiently, with a wide range of applications. It can be created from renewable energy sources and can thus serve as storage of renewable energy like wind- and sun-power. It shall be noted that Hydrogen liquefies at -252.9 °C, so cryogenic systems and sophisticated insulation techniques are necessary. Control of the flow has always been carried out by valve assemblies in processing plants. The proper design of industrial valves in every industry, including hydrogen systems, can significantly improve the safety and reliability of the valves specifically, as well as the plant as a whole. An overview of various previous studies is presented in this paper, discussing important design concepts for cryogenic valves. The main research question is to determine what are the main design considerations for valves used in liquid hydrogen systems, to minimize the risk of leakage from the valves to ensure required safety. In this study, different aspects of valve design for liquid hydrogen are examined, such as selection of steel materials, steel wall thickness calculations, stem design, sealing material selection, fire-safe design, cavity over-pressure protection, and body and bonnet extension.

DYNAMIC MODELLING OF AMMONIA CRACKERS AND HYDROGEN PEM FUEL CELLS FOR SHIPPING APPLICATIONS

The pathway towards sustainable maritime propulsion is unclear. One concept is using ammonia as a fuel. This study investigated using an ammonia cracker (a device to convert ammonia to hydrogen) and a Proton Exchange Membrane fuel cell. This requires a hydrogen buffer tank and purification, each process has been dynamically modelled. Simulations show the power demand for different vessel types (cargo and survey) for several routes. This enabled analysis of ammonia demand and system requirements during: in port; manoeuvring; cruising; surveying. The same simulations ran for other potential setups to facilitate a fair comparison of the technical challenges, storage requirements, and support system requirements (e.g. batteries). Results showed that the total system plus fuel for this concept for a case study cargo voyage would weigh 150 tonnes and require 586 m3 of volume. For comparison, a liquid hydrogen system for the same voyage weighed 35 tonnes and required 222 m3 .

Modeling on transient microstructure evolution of solid-air solidification process under continuous cooling in liquid hydrogen

The safety hazard brought by the oxygen-rich solid formed by the solidification of air in liquid hydrogen cannot be ignored. A numerical model describing the evolution of dendrite during solidification of nitrogen-oxygen binary solutions in liquid hydrogen is developed. By introducing the reduction factor, the growth anisotropy of the six-fold symmetric dendrite simulated by the Cartesian grid is effectively reduced. The reliability of the model is verified by comparing the tip growth rate of dendrites with six-fold symmetry with analytical models. On this basis, the microstructure evolution and solute segregation of solid-air dendrites are investigated. The results show that with the increase of the cooling rate, the dendrite growth rate accelerates while aggravating the solute segregation, and the outer edge of the dendrite is more likely to reach the oxygen-rich state. The improvement in solute diffusibility enables dendrites to reach an oxygen-rich state at larger sizes, but also accelerates dendrite growth. The initial composition has little effect on the microstructure evolution and growth rate of the solid-air dendrite. However, in the presence of forced convection, the solid-air dendrite morphology loses its symmetry and makes the upstream dendrite arms reach an oxygen-rich state at a smaller size. This study helps to understand the air solidification process in liquid hydrogen and provides theoretical guidance for the safety research of liquid hydrogen system.

Computing the Heat Conductivity of Fluids from Density Fluctuations.

Equilibrium molecular dynamics simulations, in combination with the Green-Kubo (GK) method, have been extensively used to compute the thermal conductivity of liquids. However, the GK method relies on an ambiguous definition of the microscopic heat flux, which depends on how one chooses to distribute energies over atoms. This ambiguity makes it problematic to employ the GK method for systems with nonpairwise interactions. In this work, we show that the hydrodynamic description of thermally driven density fluctuations can be used to obtain the thermal conductivity of a bulk fluid unambiguously, thereby bypassing the need to define the heat flux. We verify that, for a model fluid with only pairwise interactions, our method yields estimates of thermal conductivity consistent with the GK approach. We apply our approach to compute the thermal conductivity of a nonpairwise additive water model at supercritical conditions, and of a liquid hydrogen system described by a machine-learning interatomic potential, at 33GPa and 2000K.

The liquid-hydrogen absorber for MICE

This paper describes the liquid hydrogen system constructed for The Muon Ionization Cooling Experiment (MICE); MICE was built at the STFC Rutherford Appleton Laboratory to demonstrate the principle of muon beam phase-space reduction via ionization cooling. Muon beam cooling will be required at a future proton-derived neutrino factory or muon collider. Ionization cooling is achieved by passing the beam through an energy-absorbing material, such as liquid hydrogen, and then re-accelerating the beam using RF cavities. This paper describes the system creating the 22l of liquid hydrogen within the MICE beamline; the necessary safety engineering, the liquid hydrogen absorber and its associated cryogenic and gas systems are presented, along with its performance.

Consideration on possibility of cavitation induced ignition in liquid hydrogen system

Consideration on possibility of cavitation induced ignition in liquid hydrogen system

Development of a 1 L/h Scale Liquid Hydrogen System

A small-scale hydrogen liquefaction plant consists of cryocooler, cryostat, liquid nitrogen (LN2) precooling bath, two ortho–para (o–p) hydrogen converters, a heat pipe, multilayer insulations (MLI), sensors and auxiliary components. The liquefaction plant was designed as both a cryocooler-cooled liquefier and a long-term zero boil-off liquid storage reservoir. A Gifford–McMahon (GM) cryocooler was selected as a cold sink and purchased from Cryomech Inc. A vacuum-jacketed 200 L capacity cryostat was designed to provide highly efficient thermal protection to LH2 storage space. A heat pipe was uniquely designed and installed in the cryostat to enhance heat transfer between the cryocooler and hydrogen gas and liquid. A LN2-cooled precooling bath was designed to act as a precooler and an o–p hydrogen converter. MLT blankets with hydrogen getter under high vacuum in the cryostat minimize heat loss into LH2 storage. All the components were carefully assembled in dust, oil and solvent-free environment with extra caution of vacuum tightness followed by dry nitrogen and helium purge. After initial cool-down of the cryocooler under vacuum, 99.999% of 300 K hydrogen gas was introduced to the liquefaction plant. From a series of liquefaction tests with or without LN2 precooling, the hydrogen liquefaction plant successfully demonstrated 1.4 L/h of hydrogen liquefaction with LN2 precooling and two o–p hydrogen converters, and 0.7 L/h without LN2 precooling.

Influential factors for liquid acquisition device screen selection for cryogenic propulsion systems

This paper presents the influential factors which govern screen selection for liquid acquisition devices (LADs) operating in microgravity conditions for future in-space cryogenic propulsion engines and cryogenic propellant depots. Space flight requirements, which include mass flow rate, acceleration level and direction, and thermal environment, dictate screen selection for a particular mission. The five influential factors include bubble point pressure, flow-through-screen pressure drop, wicking rate, screen compliance, and material compatibility. Governing equations and analytical models for these parameters are developed from first principles. A comprehensive survey of the historical data on coarser LAD meshes over four decades of work is conducted, and liquid hydrogen data for finer Dutch Twill meshes (325 × 2300, 450 × 2750, 510 × 3600) from recently concluded experiments is also presented to validate analytical models. Each of these parameters is measurable from ground based tests, making it facile to predict flight system performance. Therefore analytical models in this paper will be valuable for future LAD designs for both cryogenic and storable propulsion systems. Additionally, analysis will be given on the impact of the factors on liquid hydrogen systems.

Special structures and properties of hydrogen nanowire confined in a single walled carbon nanotube at extreme high pressure

Extensive ab initio molecular dynamics simulations indicate that hydrogen can be confined in single walled carbon nanotubes to form high density and high pressure H2 molecular lattice, which has peculiar shell and axial structures depending on the density or pressure. The band gap of the confined H2 lattice is sensitive to the pressure. Heating the system at 2000K, the H2 lattice is firstly melted to form H2 molecular liquid, and then some of the H2 molecules dissociate accompanied by drastic molecular and atomic reactions, which have essential effect on the electronic structure of the hydrogen system. The liquid hydrogen system at 2000K is found to be a particular mixed liquid, which consists of H2 molecules, H atoms, and H-H-H trimers. The dissociated H atoms and the trimers in the liquid contribute resonance electron states at the Fermi energy to change the material properties substantially. Rapidly cooling the system from 2000K to 0.01 K, the mixed liquid is frozen to form a mixed solid melt with a clear trend of band gap closure. It indicates that this solid melt may become a superconducting nanowire when it is further compressed.

Design of a superhigh-speed cryogenic permanent magnet synchronous motor

This paper presents the design and simulation of a superhigh-speed permanent magnet synchronous motor (PMSM) that operates in the cryogenic temperature of 77 K. The designed PMSM is used to drive a two-stage cryocooler for zero boil-off and long duration storage of liquid hydrogen systems. The paper addresses electromagnetic and thermal finite-element analysis, selection of materials for cryogenic applications, stress analysis, rotor dynamic analysis, and some tradeoffs used in the design. A prototype PMSM was built to verify the design methodology.

The HARP liquid hydrogen system

A liquid hydrogen system has been developed that serves as a scatterer for the High-Acceptance Recoil Polarimeter (HARP). In order to satisfy the conflicting design requirements regarding safety, the volume of the system, the energy loss of the recoiling protons, and the location of the cryogenic unit, a self-supporting thin-walled modular cryogenic system has been developed. The system was successfully operated during two commissioning runs of HARP in a high-luminosity electron scattering environment. The operational parameters of the system have been continuously monitored and are quantitatively understood.

Damping criteria for thermal acoustic oscillations in slush and liquid hydrogen systems

Thermal acoustic oscillations in cryogenic systems are generally highly undesirable since large amounts of heat can be transferred into these systems during such oscillations. Further, the vibrations in these systems due to thermal oscillations can cause measurement and even structural difficulties. Considerable effort has been devoted in developing techniques for damping such oscillations by attaching resonators, inserting wires, etc. A theoretical analysis of these damping techniques has recently been completed. In this study a number of the damping criteria were investigated. These damping criteria were developed by investigating the stability characteristics obtained in an earlier analysis. This study indicates that thermal acoustic oscillations can be damped effectively by a number of approaches such as changing the tube radius, adjusting the length ratio of the warm section to the cold section and varying the temperature ratio or temperature profile along the tube.

Thermal acoustic oscillations in triple point liquid hydrogen systems

Thermal acoustic oscillations are often observed in tubes which penetrate a cryogenic system and are closed at the warm end and open at the cold end. Such tubes are genrally used for filling or vetning the tank, providing relief pressure or inserting instruments taps. Large amounts of heat (of the order of ten to a thousand times more than by normal heat conduction) can be transferred into a cryogenic system when such thermaloscillations occur. A number of studies examining thermal acoustic oscillations in liquid helium systems have been performed by Rott et al. However, only minimal consideration has been given to such oscillationsin liquid and sluch hydrogen systems. This study extends Rott's theory to the stability aspects of thermal acoustic oscillations for a straight tube closed at the warm end and inserted into a Dewar flask filled with triple point liquid hydrogen when the cold open end is located above the liquid surface. These results can also be applied to a slush hydrogen when the pressure in the Dewar flask is reduced to the triple point pressure of hydrogen. Numerical results have been obtained in this study for developing stability curves, establishing oscillation frequency characteristics and identifying critical configurations for initiating such oscillation. The mechanisms associated with the two branches of the stability curves for thermal acoustic oscillations have also been investigated.

Nuclear Spin Relaxation in Gases and Liquids. V. Liquid Hydrogen

The theory of nuclear spin relaxation in gases and liquids developed by Bloom and Oppenheim is applied to the liquid-hydrogen system. An explicit expression for T1 in terms of correlation functions of the anisotropic intermolecular potential is obtained. Two terms contribute to T1. The first term is independent of the ortho concentration and arises from the anisotropic potential that exists between an ortho molecule and a para molecule or the spherically symmetric part of another ortho molecule. It is suggested that three-particle correlations must be explicitly considered if one is to understand the magnitude and the temperature and density dependence of this term. The second contribution is linear in the ortho concentration and arises from the anisotropic potential between the asymmetric part of two ortho molecules (quadrupole—quadrupole interaction). Theoretical calculation of this term agrees remarkably well with experiment. It is found that a dynamical model of the molecular motions (CAA) is more satisfactory than a diffusion model (DCAA) in the calculation of the quadrupole—quadrupole interaction effects.