Variation Of Hydrogen Concentration Research Articles

Simulation and Experimental Verification of Dispersion and Explosion of Hydrogen–Methane Mixture in a Domestic Kitchen

Hydrogen is a carbon-free energy source that can be obtained from various sources. The blending of hydrogen represents a transitional phase in the shift from natural gas systems to hydrogen-based systems. However, concerns about the safety implications of introducing hydrogen have led to extensive discussions. This paper utilizes Fluent 17.0 numerical simulation software to simulate the leakage of hydrogen-blended natural gas in a closed domestic kitchen and analyze the concentration distribution and its variation pattern after a leakage. An experimental platform is set up, and a mixture of nitrogen and helium gas is used as a substitute for hydrogen-blended natural gas for the simulations and experiments. The simulation results demonstrate that the leaked gas spreads and accumulates towards the top of the space, gradually filling the entire area as the leak persists. As the hydrogen content in the leaked gas increases, the dispersion capacity of the gas in the confined space also increases. Furthermore, as the flow rate of the leaked gas increases, the average concentration of the leaked gas rises, and the gas stratification in the confined kitchen diminishes. The concentration distribution observed in the experiments aligns with the simulation results. After establishing the feasibility conditions of the model, the dispersion of the hydrogen-blended natural gas in the kitchen is further simulated. The results suggest that blending hydrogen into the gas enhances the dispersion of the gas after a leak, leading to a wider distribution within the kitchen and an increased risk in the event of a leak. Additionally, this paper employs the CASD module of FLACS 11.0 software to construct a three-dimensional geometric model of the domestic kitchen for simulation studies on the explosion of hydrogen-blended natural gas in a confined space. By adjusting the hydrogen ratio in the combustible gases present in the space and examining the variations in hydrogen concentration and external conditions, such as opening or closing the door, the influence on parameters including the peak explosion pressure, explosion overpressure, explosion flame temperature, and explosion response time are examined. Furthermore, the extent of the explosion area is determined, and the effect of hydrogen on the blast is clarified.

Effect of hydrogen traps on hydrogen permeation in X80 pipeline steel —— a joint experimental and modelling study

The permeation of hydrogen in the X80 steel was studied in this paper through thermal desorption spectroscopy, stepwise hydrogen permeation experiments and finite element modelling. Firstly, one kind of shallow trap and deep traps in X80 steel were identified through thermal desorption spectroscopy and the corresponding binding energies were obtained. According to the experiment and simulation, the deep hydrogen traps can significantly retard the first hydrogen permeation process but have almost no effect during the following charging. The X80 steel used in hydrogen compressed natural gas pipelines is exposed to hydrogen for long periods and deep traps are filled, its hydrogen permeation process is more in line with the stepwise hydrogen charging. Therefore, the stepwise hydrogen charging experiments were performed and the apparent diffusion coefficients (Dapp) and the hydrogen trap density involved in the hydrogen permeation transient (N1) were obtained using three different thickness samples. Then, a quantitative relationship in X80 steel was fitted between the N1 and the variation of hydrogen concentration. Based on the quantitative relationship and the hydrogen trap binding energies, a hydrogen permeation model in X80 steel was established. By comparing the hydrogen permeation curves obtained by our model under different boundary conditions with experiment curves, it is found that the constant concentration boundary condition model can better describe the hydrogen permeation kinetic in X80 steel under electrochemical hydrogen charging. As a result, this model can be used to predict the distribution of hydrogen in X80 steel, laying the foundation for predicting the occurrence of hydrogen embrittlement in pipeline steels.

Comparative study on the crack growth behaviours of E690 steel and heat-affected zone microstructures under cathodic potential in artificial seawater based on mechano-electrochemical effect at crack tip

The crack growth behaviours of E690 steel and HAZ microstructures under cathodic potential in artificial seawater were investigated and compared. The crack growth behaviours of three HAZ microstructures and basic metal are determined by mechano-electrochemical interaction at crack tip, and growth paths are different due to the change of microstructures. As cathodic potential negatively decreases, the crack growth rates (CGRs) of four microstructures first decrease and then increase with the minimum CGR at − 750 mV, which depends on the variation of hydrogen concentration. Applying cathodic potential is impossible to restrain crack growth, but can slow the CGR at an optimized potential.

New insights on LeTID/BO-LID in p-type mono-crystalline silicon

In this work, light-induced degradation (LID) experiments were performed on p-type boron-doped Czochralski silicon (Cz-Si) wafers under different conditions, aiming to separately characterize boron-oxygen related LID (BO-LID) and “light and elevated temperature-induced degradation” (LeTID). We found that the regeneration rate of BO-LID, as well as the extent and kinetics of LeTID, were strongly influenced by peak firing temperature. These dependences can be explained by the variation of hydrogen concentration, which was modulated by peak firing temperature. Furthermore, we found that extending the duration of dark annealing pre-treatment decelerates the subsequent regeneration of BO defects. This result revealed that, under dark annealing, the evolution of LeTID was accompanied by a notable decrease in the mobile hydrogen concentration. Supported by this phenomenon, a hydrogen-related model based on reversible reaction is proposed to describe the LeTID behavior in crystalline silicon.

Investigation on Experimental Method for Validating Performance of Passive Autocatalytic Hydrogen Recombiner

The startup and stop threshold of hydrogen recombination and the hydrogen removing rate are key performance indexes for the passive autocatalytic hydrogen recombiner (PAR). A straightforward and convenient experimental method for validating the performance of PAR is proposed. Put PAR in an airtight vessel, and hydrogen is feed to the vessel. If the PAR start hydrogen recombination and whole inlet hydrogen concentration variation curve versus time is under given line A, the startup threshold is confirmed to be not greater than A. If the final horizontal segment of the inlet hydrogen concentration variation curve versus time is under given line B, the stop threshold is confirmed to be not greater than B. If PAR realized steady operation status, the average flow rate of hydrogen fed into the vessel is the hydrogen removing rate. Test rig is designed and setup, and the experiment for validating the performance of PARQX-15 PAR is carried out. Successfully, the startup threshold is confirmed to be not greater than 2(v)%, and stop threshold is confirmed to be not greater than 0.5(v)%, and the hydrogen removing rate is greater than 536 g/h. Conclusion can be made that this method is practical and effective.

Hydrogen effect modeling on Ziegler-Natta catalyst and final product properties in propylene polymerization

Abstract
 
 Hydrogen, as chain transfer agent, effects on kinetic of propylene polymerization; consequently variation of hydrogen concentration leads to change final product properties and also activates site of used catalyst. This phenomenon is one of the most important process variables is to adjust the final product properties and optimize the operating conditions. This work has attempted to present a mathematical model that cable to calculate the most important indices of end used product, such as melt flow index, number and weight average molecular weight and poly dispersity index. The model can predict profile polymerization rates determining important kinetic parameters such as the activation energy, lumped deactivation reaction initial reaction rate and deactivation constant. The mathematical model was implemented in Matlab/Simulink environment for slurry polymerization in laboratory scale. The modeling approach is based on polymer moment balance method in the slurry semi-batch reactor. In addition, in this work have provided a model that calculating fraction activated sites catalyst via hydrogen concentration. The model was validated by experimental data from lab scale, reactor. The experimental and model outputs were compared; consequently, the errors were within acceptable range.
 KEY WORDS: Mathematical modeling, Propylene polymerization, Kinetics study, Hydrogen response, population balance
 Bull. Chem. Soc. Ethiop. 2018, 32(2), 371-386.
 DOI:https://dx.doi.org/10.4314/bcse.v32i2.15

Plasmonic Metal-Hybrid Hydrogen Sensor Based on Semiconductor Nanocrystal Micro Ring

ABSTRACTWe have proposed and demonstrated numerically an ultra-small (4×4μm2) hydrogen sensor based on micro ring resonator. With a palladium or platinum layer coated on the inner surface of the micro ring resonator, the device is highly sensitive to the low hydrogen concentration variation and the sensitivity is at least one magnitude order larger than the optical fiber-based hydrogen sensor. We have also investigated the tradeoff between the portion coverage of palladium/platinum layer and the sensitivity. The width of the hydrogen sensitive layer is also studied and the minimum feature width is determined to be the length of the ring waveguide evanescent wave. This ultra-small optical hydrogen sensor will be promising to realize highly compact sensor with integration capability for applications on hydrogen fuel economy.

A New Hydrogen Sensor Based on SNS Fiber Interferometer with Pd/WO₃ Coating.

This paper presents a new hydrogen sensor based on a single mode–no core–single mode (SNS) fiber interferometer structure. The surface of the no core fiber (NCF) was coated by Pd/WO3 film to detect the variation of hydrogen concentration. If the hydrogen concentration changes, the refractive index of the Pd/WO3 film as well as the boundary condition for light propagating in the NCF will all be changed, which will then cause a shift into the resonant wavelength of interferometer. Therefore, the hydrogen concentration can be deduced by measuring the shift of the resonant wavelength. Experimental results demonstrated that this proposed sensor had a high detection sensitivity of 1.26857 nm/%, with good linearity and high accuracy (maximum 0.0055% hydrogen volume error). Besides, it also possessed the advantages of simple structure, low cost, good stability, and repeatability.

Factors influencing hydrogen flux in a fault zone of Henan Province, China

This research investigates the main factors influencing changes in hydrogen concentration in a fault zone and analyzes the relationship between hydrogen and tectonic activity. Based on the hydrogen concentration in the fault gas and continuous observation data from Mashankou, Neixiang County, Henan Province, the relationships between the variation in hydrogen concentration and ground temperature, atmospheric temperature, and atmospheric pressure are analyzed. In addition, the earth tide effect on hydrogen in the fault zone is discussed. The results show that the direct influence of atmospheric or ground temperatures on the hydrogen concentration is not significant. The atmospheric and ground temperatures have some impact on the hydrogen concentration only when ground temperature increases. By means of a wavelet analysis method, which separates the semidiurnal wave and diurnal wave signals of hydrogen, the results show that the hydrogen concentration is capable of indicating the solid earth tide when comparing the pressure tide and solid earth tide signals in the same period.

Ring Resonator-Based Optical Hydrogen Sensor

We have proposed and demonstrated numerically a ultra-small and highly sensitive hydrogen sensor, based on micro ring resonator with a footprint size as small as 4×4 μm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . With a palladium or platinum hydrogen sensitive layer coated on the inner surface of the micro ring resonator, the device is highly sensitive to the low hydrogen concentration variation and the sensitivity is at least one magnitude order larger than the optical fiber-based hydrogen sensor. We have also investigated the tradeoff between the portion coverage of palladium/platinum layer and the sensitivity. The width of the hydrogen sensitive layer is also studied and the minimum feature width is determined to be the length of the ring waveguide evanescent wave. This ultra-small optical hydrogen sensor will be promising to realize highly compact sensor with integration capability for applications on hydrogen fuel economy.

Effects of hydrogen pressure on hydrogenated amorphous silicon thin films prepared by low‐temperature reactive pulsed laser deposition

We deposit intrinsic hydrogenated amorphous silicon (a‐Si:H) thin films by reactive pulsed laser deposition, for various hydrogen pressures in the 0–20 Pa range, at a low deposition temperature of 120 °C, and investigate the hydrogen incorporation, structural, optical, and electrical properties of the films, as a function of the ambient hydrogen pressure. The film thickness decreases linearly as the hydrogen pressure increases. The hydrogen content of the films is determined by infrared spectroscopy and the optical bandgap from UV‐Vis‐NIR transmittance and reflectance measurements. Electric measurements yield the dark conductivity of the films. The hydrogen concentration of the films lies in the 1021–1022cm–3 range and increases with the hydrogen pressure until the latter reaches 15 Pa, beyond which the hydrogen concentration decreases. The optical bandgap and dark conductivity follow the hydrogen concentration variation of the films. The dark conductivity lies in the 10–9–10–10S/cm range. An unusually wide optical bandgap of 2.2–2.6 eV is observed.

Modelling of measured optical properties of Pd–Au alloy ultrathin film for room temperature hydrogen sensing

A theoretical framework is presented to describe optical properties of palladium gold alloy ultra‐thin film of thickness about 5 nm. Density functional theory is employed to calculate complex dielectric function of hydrogen loaded Pd3Au alloy. Using Bruggeman's effective medium theory, the effective dielectric function of hydrogenated alloy is calculated in case of non‐uniform diffusion of hydrogen starting from very low concentration. Reflectance of deposited film on silica substrate is calculated using transfer matrix method and results are compared with the measured reflectance of sputter deposited thin film of alloy on identical substrate. The change of reflectance with hydrogen concentration is also calculated and verified experimentally. In both the cases, hydrogen loaded films show low reflectance due to reduction of the available electronic states near Fermi level compared to unloaded films. From TEM images and Grazing Incidence X‐ray diffraction analyses, crystal structure of the deposited alloy film is predicted. Using this alloy a four‐layered plasmonic waveguide is designed for room temperature hydrogen sensing. Analytical calculations show that absorption loss of fundamental TM mode of the waveguide at 633 nm changes almost linearly with hydrogen concentration variation. The loss will decrease about 5 dB/100% atomic concentration of hydrogen for 10 µm device length.

About Nuclear Resonant Reaction Analysis for Hydrogen Investigations in Amorphous Silicon

Nuclear Resonant Reaction Analysis (NRRA) is a common method detecting the nearsurface hydrogen distribution of a sample in a depth of up to a few microns. The mass density and related stopping power of a hydrogenated amorphous silicon (a-Si:H) layer depends on the hydrogen content. Correct hydrogen depth profiles are calculated considering the effective ion beam stopping crosssection as well as the related stopping power of the investigated film. The consideration of the local hydrogen concentration is important to avoid misinterpretations of the hydrogen distribution regarding profile depth. Therefore, stopping powers have to be considered carefully when interpreting hydrogen depth profiles especially of films that exhibit variations in hydrogen concentration. Moreover, further investigations like morphology dependent changes of the effective stoppingcross section are not possible without correctly calculated hydrogen depth profiles. Here the correct way is presented how to consider the embedded hydrogen of an a-Si:H layer when calculating absolute depth information of a NRRA measured hydrogen depth profile.

Hydrogen concentration variation and examination of PAR installation in reactor containment building during hydrogen release from different direction failure places

Concentration on a hydrogen explosion mitigation strategy increased after the accident in Fukushima. A passive autocatalytic recombiner (PAR) is considered as the most realistic mitigation technology during a severe accident where electric power is lost. Hydrogen distribution and concentration might be accurately predicted because PAR must be installed in a place having a proper amount of hydrogen in order to produce positive performance. In this paper, hydrogen distributions and concentrations were predicted and analyzed during hydrogen release from different direction failure places, and then PAR installation was examined. The result shows that the hydrogen concentrations are randomly changed in the containment overall, and the behavior of hydrogen in the case of upper part failure is completely different from the case of a side part failure. It is expected that PAR works well in the area among small compartments located at the lower part of the containment building; however, the performance of PAR installed on another area is inferior.

Hydrogen trapping in high strength martensitic steel after austenitized at different temperatures

Hydrogen trapping behavior has been investigated by means of thermal desorption spectrometry (TDS) for a high strength steel after it is austenitized at the temperature range of 880–1250 °C, oil quenched, and tempered at 200 °C. Results show that with increasing austenitizing temperature, the pre-charged hydrogen concentration in the steel first decreases and then increases, being the lowest value at the austenitizing temperature of 1050 °C. The variation of hydrogen concentration with austenitizing temperature is related to the differences in the prior austenite grain size and solute Nb content, which may act as shallow hydrogen traps in the steel. The difference in the pre-charged hydrogen concentration can account for the previously reported result on delayed fracture resistance of the steel after austenitized at different temperatures.

Hydrogen Absorption and Magnetic Properties of HO&lt;sub&gt;2&lt;/sub&gt;Fe&lt;sub&gt;14&lt;/sub&gt;BH&lt;sub&gt;x&lt;/sub&gt; Hydrides

Magnetic properties of the hydrides of an intermetallic compound Ho2Fe14B are studied in the temperature range 78 700 K. The temperature dependencies of magnetization σ (Т) are obtained under continuous control of the hydrogen content in the samples investigated. The dependence of the Curie (TC) and the spin-reorientation transition (TSR) temperatures on hydrogen pressure (P) and its concentration (x) are determined. The dependence of hydrogen concentration on pressure at constant temperatures (isotherms x (P)) in the vicinity of TC and the temperature variation of hydrogen concentration at a constant pressure (isobars x (T)) are investigated.

A passive wireless hydrogen surface acoustic wave sensor based on Pt-coated ZnOnanorods

Using a passive wireless sensor to detect hydrogen can reach the goals of reducing cost andincreasing the lifetime since the sensor can work without batteries. In this paper, a passivewireless hydrogen SAW sensor operating at room temperature has been achieved bycombining a SAW tag and a resistive hydrogen sensor. The SAW tag is fabricated on a128°YX-LiNbO3 substrate and its central frequency is 433 MHz. The resistive hydrogen sensor with thePt-coated ZnO nanorods as the sensing film has the advantages of high stability, goodrepeatability and simple fabrication. The ZnO nanorods are synthesized by using theaqueous solution method and the Pt coating is employed as a catalyst for the hydrogendetection. The property of the resistive hydrogen sensor is examined before combining withthe SAW tag. Results show that the resistance changes caused by the variations of relativehumidity and temperature are negligible. Finally, the hydrogen SAW sensor is configuredand measured wirelessly for various hydrogen concentrations at room temperature. Thedifference of the relative return loss caused by the hydrogen concentration variation isobvious and recognizable. All responses show that the proposed hydrogen sensor not onlyhas good repeatability and high sensitivity but is capable of passive wireless detection.

Influence of hydrogen on the formation of a thin layer of carbon nanofibers on Ni foam

Carbon nanofibers (CNFs) were catalytically grown on Ni foam by decomposing ethylene in the presence of hydrogen. Variation of hydrogen concentration during CNF growth resulted in significant manipulation of the properties of a thin layer of CNFs. Addition of hydrogen retards carbon deposition and increases the surface area of the CNF layer because of formation of thinner fibers. The thickness of CNF layer shows an optimum at intermediate hydrogen concentrations. These effects contribute to the competitive adsorption of hydrogen and ethylene, influencing the availability of carbon on the Ni surface, which is necessary for both the formation of small Ni particles by fragmentation of polycrystalline Ni, as well as for CNF growth after formation of small particles. Furthermore, decreasing the carbon supply via adding hydrogen also delays deactivation by encapsulation of Ni particles. The thickness of the micro-porous C-layer between the Ni surface and the CNF layer decreases with hydrogen addition, at the expense of a slight loss in the attachment of the CNFs to the foam, supporting the proposition that CNFs are attached by roots in the C-layer. The addition of hydrogen after the initial CNF formation in ethylene only causes fragmentation of the C-layer, inducing significant loss of CNFs.

Swine manure fermentation for hydrogen production

Biohydrogen fermentation using liquid swine manure as substrate supplemented with glucose was investigated in this project. Experiments were conducted using a semi-continuously-fed fermenter (8 L in total volume and 4 L in working volume) with varying pHs from 4.7 through 5.9 under controlled temperature (35 ± 1 °C). The hydraulic retention time (HRT) tested include 16, 20, and 24 h; however, in two pH conditions (5.0 and 5.3), an additional HRT of 12 h was also tried. The experimental design combining HRT and pH provided insight on the fermenter performance in terms of hydrogen generation. The results indicated that both HRT and pH had profound influences on fermentative hydrogen productivity. A rising HRT would lead to greater variation in hydrogen concentration in the offgas and the best HRT was found to be 16 h for the fermenter in this study. The best pH value in correspondence to the highest hydrogen generation was revealed to be 5.0 among all the pHs studied. There was no obvious inhibition on hydrogen production by methanogenesis when methane content in the offgas was lower than 2%. Otherwise, an inverse linear relationship between hydrogen and methane content was observed with a correlation coefficient of 0.9699. Therefore, to increase hydrogen content in the offgas, methane production has to be limited to below 2%.

A room temperature surface acoustic wave hydrogen sensor with Pt coated ZnOnanorods

A surface acoustic wave (SAW) sensor with Pt coated ZnO nanorods as the selective layerhas been investigated for hydrogen detection. The SAW sensor was fabricated based on a128°YX-LiNbO3 substrate with a operating frequency of 145 MHz. A dual delay line configuration wasadopted to eliminate external environmental fluctuations. The Pt coated ZnO nanorodswere chosen as a selective layer due to their high surface-to-volume ratio, large penetrationdepth, and fast charge diffusion rate. The ZnO nanorods were synthesized byan aqueous solution method and coated with the noble metal Pt as a catalyst.Finally, the SAW sensor responses to humidity and hydrogen were tested. Resultsshow that the sensor is not sensitive to humidity; moreover, the frequency shiftfor a hydrogen concentration variation of 6000 ppm is 26 kHz while operating atroom temperature. It can be concluded that the Pt coated ZnO nanorod basedSAW hydrogen sensor exhibits fast response, good sensitivity and short-termrepeatability. It is worth noting that not only is the sensor sensitive enough tooperate at room temperature, but also it can avoid the influence of humidity.