Hydrogen Concentration Distribution Research Articles

Influence of the Stress-Strain State on the Distribution of Hydrogen Concentration in the Process Zone

We propose a theoretical-experimental approach to the determination of the concentration of hydrogen in the process zone. The plots of the dependences of the concentration of hydrogen on the mechanical characteristics of the material and external load are constructed.

Analysis of the Kinetics of Hydrogen Redistribution in Bimetallic Joints

We propose an algorithm for the solution of the problem of heat conduction and hydrogen diffusion with variable coefficients of diffusion and solubility for structurally inhomogeneous materials. As an example, we test the algorithm by solving the problem for bimetallic cylindrical specimens used, according to the ASTM G146-01 standard, for the investigation of the hydrogen resistance of bimetallic joints. We determine the distribution of hydrogen concentration in cylindrical specimens with weld overlay obtained as a result of cooling at different rates after high-temperature hydrogenation. It is shown that, in the fusion zone (on the side of the coating), we observe the formation of the zones of superequilibrium supersaturation with hydrogen, which may result in the exfoliation of the weld overlay from the base metal.

Highly sensitive secondary ion mass spectrometric analysis of time variation of hydrogen spatial distribution in austenitic stainless steel at room temperature in vacuum

Hydrogen contained in austenitic stainless steel is classified as diffusible or nondiffusible. The hydrogen distribution in austenitic stainless steel changes with time owing to hydrogen diffusion at room temperature, and such changes in hydrogen distribution cause the mechanical properties of the steel to change as well. It is therefore important to analyze the time variation of the hydrogen distribution in austenitic stainless steel at room temperature to elucidate the effects of hydrogen on the steel's mechanical properties. In this study, we used secondary ion mass spectrometry (SIMS), a highly sensitive detection method, to analyze the time variation of the distribution of hydrogen charged into 316L austenitic stainless steel. SIMS depth profiles of hydrogen that were acquired at the three measurement times were analyzed, and the results were compared among the measurement times. 1H− intensities and distribution of the intensities changed with time due to diffusion of hydrogen in the hydrogen-charged 316L steel sample at room temperature. Moreover, the time variation of the hydrogen concentration distribution of the hydrogen-charged 316L sample was calculated using a one-dimensional model based on Fick's second law. The time variations of the measured hydrogen intensities and of the calculated values are compared.

PTFE-nafion membrane reactor for hydrogen production

This paper presents an experimental and modelling study of the kinetics of hydrogen production through the methanol steam reforming (MSR) process using a membrane reactor with a self-made, porous PTFE-nafion membrane. The operating conditions were optimised through an analysis of the hydrogen recovery and the CO selectivity. The membrane reactor was modelled based on the hydrogen production rate, which was linked (chain) to the changes in the reactant concentrations. The analysis of the reaction kinetics provided an overview of the reaction process and the factors that affect the process. Moreover, the size of the membrane was estimated using the distribution of hydrogen concentrations along the reactor. The separation factors, particularly the separation of hydrogen from CO and CO2, are some of the factors that can influence the performance of a membrane reactor.

Simulation of Flow Field Pattern Influence on the Hydrogen Consumption in A PEMFC

Simulations results are presented in this paper, which were obtained on investigating the effects of flow patterns on the hydrogen consumption in a proton exchange membrane fuel cell (PEMFC). In this study, a 3-D computational model was developed to investigate the influence of the flow and depth of the channels on hydrogen consumption. Simulation results showed the influence of depth in the distribution of hydrogen concentration. The flow channel pattern adopted in this study is the serpentine flow channel.

The failure criterion based on hydrogen distribution ahead of the fatigue crack tip

The hydrogen effect on the fracture toughness and fatigue crack growth behaviour in the martensitic high strength steel is investigated. The secondary ion mass spectrometry method has been employed to analyse the distribution of hydrogen concentration in the zone of the crack tip and at its edges. Changes in hydrogen concentration are observed in the vicinity of the propagating crack tip and at a remote site. The hydrogen peak H C is reduced and moves away from the fatigue crack tip with the increase of the maximum stress intensity factor max K . The concept of damage evolution is used to explain fatigue crack propagation in connection with the hydrogen redistribution ahead of the crack tip. The physical failure criterion based on the hydrogen peak in the vicinity of the fatigue crack tip and the maximum stress intensity factor has been proposed. The criterion reflects changes in the hydrogen peak which resulted from the hydrogen redistribution due to the increase of the maximum stress intensity factor as the crack length increases under fatigue loading.

Ignition and heat radiation of cryogenic hydrogen jets

In the present work release and ignition experiments with horizontal cryogenic hydrogen jets at temperatures of 35–65 K and pressures from 0.7 to 3.5 MPa were performed in the ICESAFE facility at KIT. This facility is specially designed for experiments under steady-state sonic release conditions with constant temperature and pressure in the hydrogen reservoir. In distribution experiments the temperature, velocity, turbulence and concentration distribution of hydrogen with different circular nozzle diameters and reservoir conditions was investigated for releases into stagnant ambient air. Subsequent combustion experiments of hydrogen jets included investigations on the stability of the flame and its propagation behaviour as function of the ignition position. Furthermore combustion pressures and heat radiation from the sonic jet flame during the combustion process were measured. Safety distances were evaluated and an extrapolation model to other jet conditions was proposed. The results of this work provide novel data on cryogenic sonic hydrogen jets and give information on the hazard potential arising from leaks in liquid hydrogen reservoirs.

Simulation of hydrogen distribution in an Indian Nuclear Reactor Containment

The management of hydrogen in a Nuclear Reactor Containment after LOCA (Loss Of Coolant Accident) is of practical importance to preserve the structural integrity of the containment. This paper presents the results of systematic work carried out using the commercial Computational Fluid Dynamics (CFD) software FLUENT to assess the concentration distribution of hydrogen in a typical Indian Nuclear Reactor Containment. In order to obtain an accurate estimate of hydrogen concentration distribution, a suitable model for turbulence closure is required to be selected. Using guidelines from the previous studies reported in the literature and a comparative simulation study using simple benchmark problems, the most suitable turbulence model for hydrogen mixing prediction was identified. Subsequently, unstructured meshes were generated to represent the containment of a typical Indian Nuclear Reactor. Analyses were carried out to quantify the hydrogen distribution for three cases. These were (1) Uniform injection of hydrogen for a given period of time at room temperature, (2) Time varying injection as has been computed from an accident analysis code, (3) Time varying injection (as used in case (2)) at a high temperature. A parametric exercise was also carried out in case (1) where the effect of various inlet orientations and locations on hydrogen distribution was studied. The results indicate that the process of hydrogen dispersal is buoyancy dominated. Further for typical injection rates encountered following LOCA, the dispersal is quite poor and most hydrogen is confined to the fuelling machine vault.

Cr-Mo-V鋼多層溶接部における水素濃度分布

It has developed the numerical simulation method of hydrogen diffusion for multi-layer weld on Cr-Mo-V steel. The developed simulation method can estimate the distribution of hydrogen concentration on weld metal and predict reduction of hydrogen by various dehydrogenation heat treatment conditions. The accuracy of calculation is practically enough for selecting the condition to prevent a cold cracking.In order to improve the accuracy of the calculation of hydrogen diffusion on weld, it is necessary to input the actual thermal history and initial hydrogen concentration into the calculation model. Also, it is important to model the hydrogen diffusion corresponding to the real phenomenon. It has found that the hydrogen degassing rate of Cr-Mo-V steel was slower than the conventional steel from measured data by gas chromatography. The hydrogen concentration was the maximum at the position of slightly inside from surface of last weld side. If it was compared the reduction of hydrogen concentration of 623K 4 hours and 553K 6 hours, the 623K 4 hours is much effected. However, when the longer time at 553K DHT is applied, it is expected further reduction of hydrogen concentration.

Two-Dimensional Numerical Modelling of Hydrogen Diffusion in Metals Assisted by Both Stress and Strain

The present work is based on previous research on the one-dimensional (1D) analysis of the hydrogen diffusion process, and proposes a numerical approach of the same phenomenon in two-dimensional (2D) situations, e.g. notches. The weighted residual method was used to solve numerically the differential equations set out when the geometry was discretized through the application of the finite element method. Three-node triangular elements were used in the discretization, due to its simplicity, and a numerical algorithm was numerically implemented to obtain the hydrogen concentration distribution in the material at different time increments. The model is a powerful tool to analyze hydrogen embrittlement phenomena in structural materials.

The structure and flame propagation regimes in turbulent hydrogen jets

Experiments on flame propagation regimes in a turbulent hydrogen jet with velocity and hydrogen concentration gradients have been performed. Horizontal stationary hydrogen jets released at normal and cryogenic temperatures of 290, 80 and 35K with different nozzle diameters and mass flow rates have been investigated. Sampling probe method and laser PIV techniques have been used to evaluate the distribution of hydrogen concentration and flow velocity. High-speed photography combined with a Background Oriented Schlieren (BOS) system was used for the visual observation of the turbulent flame propagation. In order to investigate different flame propagation regimes the ignition position was changed along the jet axis. It was found that the flame propagates in both directions, up- and downstream of the jet flow if hydrogen concentration is >11%, whereas in case [H2] < 11%, the flame propagates only downstream. This means that at normal temperature the flame is able to accelerate effectively only if the expansion ratio σ of the H2-air mixture is higher than a critical value σ* = 3.75 defined for a closed geometry.

Simulation of small-scale releases from liquid hydrogen storage systems

Knowledge of the concentration field and flammability envelope from small-scale leaks is important for the safe use of hydrogen. These small-scale leaks may occur from leaky fittings or o-ring seals on liquid hydrogen-based systems. The present study focuses on steady-state leaks with large amounts of pressure drop along the leak path such that hydrogen enters the atmosphere at near atmospheric pressure (i.e. Very low Mach number). A three-stage buoyant turbulent entrainment model is developed to predict the properties (trajectory, hydrogen concentration and temperature) of a jet emanating from the leak. Atmospheric hydrogen properties (temperature and quality) at the leak plane depend on the storage pressure and whether the leak occurs from the saturated vapor space or saturated liquid space. In the first stage of the entrainment model ambient temperature air (295 K) mixes with the leaking hydrogen (20–30 K) over a short distance creating an ideal gas mixture at low temperature (∼65 K). During this process states of hydrogen and air are determined from equilibrium thermodynamics using models developed by NIST. In the second stage of the model (also relatively short in distance) the radial distribution of hydrogen concentration and velocity in the jet develops into a Gaussian profile characteristic of free jets. The third and by far the longest stage is the part of the jet trajectory where flow is fully developed. Results show that flammability envelopes for cold hydrogen jets are generally larger than those of ambient temperature jets. While trajectories for ambient temperature jets depend solely on the leak densimetric Froude number, results from the present study show that cold jet trajectories depend on the Froude number and the initial jet density ratio. Furthermore, the flammability envelope is influenced by the hydrogen concentration in the jet at the beginning of fully developed flow.

Numerical modeling of detonation combustion of hydrogen-air mixtures in a convergent-divergent nozzle

The flow of igniting hydrogen-air mixtures entering an axisymmetric convergent-divergent nozzle at a supersonic velocity is considered. A possibility of stabilizing detonation combustion is numerically investigated at different freestream Mach numbers with account for nonuniform distribution of hydrogen concentration at the nozzle entry. The investigation is performed on the basis of the two-dimensional gasdynamic Euler equations for a multicomponent reacting gas. A detailed model of chemical reactions is used. The calculated thrust is compared with the drag of a conical housing containing the supersonic nozzle considered.

Ex-situ and in-situ Neutron Radiography Investigations of the Hydrogen Uptake of Nuclear Fuel Cladding Materials During Steam Oxidation at 1000°C and Above

AbstractNeutron radiography is a powerful tool for the investigation of the hydrogen uptake of zirconium alloys. It is fast, fully quantitative, non-destructive and provides a spatial resolution of 30 μm. The non-destructive character of neutron radiography provides the possibility of in-situ investigations. The paper describes the calibration of the method and delivers results of ex-situ measurements of the hydrogen concentration distribution after steam oxidation, as well as in-situ experiments of hydrogen diffusion in β-Zr and in-situ investigations of the hydrogen uptake during steam oxidation.

Behavior of Hydrogen Atoms in Perovskite-Type Oxide Thin Films under Electric Fields

The behavior of hydrogen in (Ba,Sr)TiO3 (BST) thin film capacitors under electric fields was investigated by performing secondary ion mass spectroscopy (SIMS) analyses. It was clearly observed that the ingress of atmospheric hydrogen into BST thin film capacitors occurred through the anode and that it diffused toward the cathode under electric fields. In addition, it was found that the deterioration of the I-V properties of the BST thin film capacitors can be interpreted in terms of the distribution of hydrogen concentration in the BST thin films.

Mixture distribution measurement using laser induced breakdown spectroscopy in hydrogen direct injection stratified charge

Reduction in cooling loss due to the heat transfer from burning gas to the combustion chamber wall is very important for improving the thermal efficiency in hydrogen engines. The previous research has shown that the direct injection stratified charge can be a technique to reduce the cooling loss and improve thermal efficiency in hydrogen combustion. For effective reductions in cooling loss by the stratified charge, it is very important to know the relation between the fuel injection conditions and mixture distribution. The current research employs the laser induced breakdown spectroscopy as a method to measure the hydrogen concentration distribution in the direct injection stratified charge. Measurement of instantaneous local equivalence ratio by the method clears the characteristics of mixture formation in hydrogen direct injection stratified charge. This research also tries to actively control the mixture distribution using a split fuel injection.

Boundary layer theory approach to the concentration layer adjacent to a ceiling wall of a hydrogen leakage: Far region

The field of the hydrogen leakage in partially open space can be divided into two main regions according to the importance of the hydrogen concentration distribution and the flow behavior. These two regions are the jet region and the boundary layer region which are adjacent to the ceiling wall of the space, resulting from impinging the hydrogen jet to the wall. The boundary layer region in turn can be divided into two regions, according to the modeling of the flow. These regions are the stagnation-point boundary layer region and the far boundary layer region. Previously, we studied the region of stagnation-point flow (Hiemenz flow) [El-Amin MF, Kanayama H. Boundary layer theory approach to the concentration layer adjacent to a ceiling wall at impinging region of a hydrogen leakage. Int J Hydrogen Energy, in press.]. The current paper is devoted to analyze the far region of the boundary layer adjacent to the ceiling wall using the boundary layer theory. Also, an experiment has been conducted on the hydrogen leakage in partially open space to estimate the concentration distribution vertically at the center of the domain under the ceiling wall. In order to verify the boundary layer theory approach, a comparison between the measurements and the boundary layer theory approximations is investigated and the results showed a good agreement. The wall shear stress, the local friction factor, the friction drag and the non-dimensional drag coefficient of the ceiling wall are calculated. Also, both momentum and concentration boundary layer thicknesses are estimated.

The effect of ventilation system design on hydrogen dispersion in a sedan

The dispersion of hydrogen leaking from a fuel tank of a hydrogen-powered sedan into its interior is simulated in this paper. The effects of two different ventilation systems on the evacuation of the hydrogen are compared. Results are presented as illustrations of the steady state hydrogen concentration distribution in the sedan. The study demonstrates that a modified ventilation system can greatly reduce the risk of hydrogen combustion or explosion in the sedan interior.

Hydrogen Concentration Distribution in Simulated Spaces for a Hydrogen System Installed in a Large Bus in Case of Hydrogen Leakage

Hydrogen Concentration Distribution in Simulated Spaces for a Hydrogen System Installed in a Large Bus in Case of Hydrogen Leakage

Consequence analysis and safety verification of hydrogen fueling stations using CFD simulation

Now that environmental awareness is enhanced on a global basis, great hopes are placed on the expanded use of hydrogen stations and fuel-cell vehicles (FCVs) that economize hydrogen energy. Hydrogen stations must be safe and secure because they store large quantities of hydrogen under higher pressure than the hydrogen actually consumed by FCVs. Thus, multiple safety measures are taken to ensure that hydrogen does not leak from the stations. Furthermore, in the unlikely event of leakage, the damage needs to be kept on an allowable level. For this reason, it is necessary to understand the behavior of hydrogen gas leaking from the stations.It is well known that hydrogen is a highly explosive gas, being combustible over a wide range of concentrations. Due to this property of hydrogen, tests for verifying its behavior must be done outdoors. In the open air, however, tests are affected by weather conditions and hydrogen sensors’ responses are delayed, which makes it difficult to observe an accurate distribution of hydrogen concentrations. Therefore, with respect to assumed cases of hydrogen leakage, a concentration distribution of hydrogen gas was obtained by means of computational fluid dynamics (CFD). The analysis results were used for verifying the safety of hydrogen stations.