Hydrogen Concentration In Air Research Articles

Low frequency quartz tuning fork as hydrogen sensor

The use of hydrogen as a sustainable energy source is pushing the development of innovative sensing strategies for the monitoring of H2 concentration during its production processes and transportation. In this work, we propose a custom quartz tuning fork (QTF) as sensor for the detection of high concentrations of hydrogen in air. The selectivity derives directly from values of molar mass and the viscosity of hydrogen molecules, significantly different from those of the other main constituents of air. Exciting the fundamental flexural mode of a commercially available 12.4 kHz-QTF, we demonstrated the linear dependence of its resonance frequency and quality factor on the H2 concentration, passing through their relationship with molar mass and the viscosity of the H2-air mixture. Monitoring the shift of the resonance frequency of the QTF, the H2-component in air can be estimated with a precision level of 0.74% and accuracy error of 1.82%. The same parameters resulted 0.40% and 4.29%, respectively, when Q values are evaluated. Finally, a beat-frequency approach was proposed to speed up the acquisition in few seconds, monitoring both resonance parameters of the QTF.

Minimum Detection Concentration of Hydrogen in Air Depending on Substrate Type and Design of the 3ω Sensor.

Hydrogen has emerged as a promising carbon-neutral fuel source, spurring research and development efforts to facilitate its widespread adoption. However, the safe handling of hydrogen requires precise leak detection sensors due to its low activation energy and explosive potential. Various detection methods exist, with thermal conductivity measurement being a prominent technique for quantifying hydrogen concentrations. However, challenges remain in achieving high measurement sensitivity at low hydrogen concentrations below 1% for thermal-conductivity-based hydrogen sensors. Recent research explores the 3ω method's application for measuring hydrogen concentrations in ambient air, offering high spatial and temporal resolutions. This study aims to enhance hydrogen leak detection sensitivity using the 3ω method by conducting thermal analyses on sensor design variables. Factors including substrate material, type, and sensor geometry significantly impact the measurement sensitivity. Comparative evaluations consider the minimum detectable hydrogen concentration while accounting for the uncertainty of the 3ω signal. The proposed suspended-type 3ω sensor is capable of detecting hydrogen leaks in ambient air and provides real-time measurements that are ideal for monitoring hydrogen diffusion. This research serves to bridge the gap between precision and real-time monitoring of hydrogen leak detection, promising significant advancements in the related safety applications.

The critical mass for the unconfined vapour cloud explosion of compressed and liquid hydrogen

AbstractThe (unconfined) vapour cloud explosion (VCE) is a dramatic phenomenon that generates a severe pressure wave with a high potential to damage assets and produce injuries in the far field. This definition applies also to hydrogen. Nevertheless, no clear tools and methodology have been so far developed and tested for this highly reactive gas, and even advanced numerical simulations lack validation and suffer from large uncertainties. In this view, the comprehension of the physic which subtends this dramatic phenomenon for the specific case of hydrogen is still a central issue. This paper revises some of the most adopted theories on VCE based on classical acoustic theory and models for pressure wave propagation and provides a consequence‐based, threshold (minimum) value for the critical mass of hydrogen which is needed—at a stoichiometric concentration in air—for a vapour cloud to behave as a VCE. To this regard, any non‐stoichiometric hydrogen concentration in air or lower amount of hydrogen would decrease either the flame Mach number or the total energy, thus resulting in negligible overpressure. In this sense, the effects of buoyancy, diffusivity, and weather conditions on the dispersion of hydrogen should be taken into account. The results are valid either for compressed or cryogenic liquid tanks and can be adopted for the sake of distinction between hydrogen flash fire and VCE; for the hazard analysis of hydrogen production and storage; and more in general for the risk assessment of hydrogen systems.

Solid-Oxide Amperometric Sensor for Hydrogen Detection in Air

An amperometric sensor based on CaZr0.95Sc0.05O3−δ (CZS) proton-conducting oxide for the measurement of hydrogen concentration in air was designed and tested. Dense CZS ceramics were fabricated through uniaxial pressing the powder synthesized by the solid-state method and sintering at 1650 °C for 2 h. The conductivity of CZS was shown to increase with increasing air humidity, which indicates the proton type of conductivity. The sensor was made from two CZS plates, one of which had a cavity was drilled to form an inner chamber, that were then pressed against each other and sealed around the perimeter to prevent gas leaking. The inner chamber of the sensor was connected with the outer atmosphere via an alumina ceramic capillary, which acted as a diffusion barrier. The sensor performance was studied in the temperature range of 600–700 °C in the mixtures of air with hydrogen. The sensor signal, or the limiting current, was found to linearly increase with the hydrogen concentration, which simplifies the sensor calibration. The sensor demonstrated a high sensitivity of ~60 μA per 1% H2 at 700 °C, a fast response, high reproducibility, good selectivity, and long-term stability.

Sensor Based on a Solid Oxide Electrolyte for Measuring the Water-Vapor and Hydrogen Content in Air

The present communication describes the results of the performance and the assessment of a sensor based on a solid oxide electrolyte with a composition of 0.9ZrO2 + 0.1Y2O3 (YSZ), equipped with a ceramic diffusion barrier for measuring the water vapor and hydrogen content in air. The possibility of determining the concentration of water vapor and hydrogen in the air is based on the measurement of the limiting current value. For the calculation of the steam and hydrogen concentration in ambient air, analytical expressions were obtained and applied, using the limiting current values measured in air with a standard oxygen concentration of 20.9 vol.% and in the analyzed air. A two-stage method for the determination of the hydrogen and steam amount in ambient air is proposed. It is stated that the sensor operates successfully at the temperature of 700 °C and can be applied for the continuous determination of steam or hydrogen concentrations in air.

Development of Highly Sensitive and Stable Surface Acoustic Wave‐Based Hydrogen Sensor and Its Interface Electronics

AbstractA surface acoustic wave (SAW)‐based hydrogen sensor and its corresponding interface electronics have been developed to measure the hydrogen concentration in air at room temperature. Two SAW delay lines with center frequencies of 284 and 284.3 MHz are employed for the sensor system to eliminate any environmental disturbances emerging from temperature and humidity variations on a sensor output. A beehive‐configured and Cu‐doped SnO2 nanostructure is used as a hydrogen‐sensitive material to have a high surface to volume ratio, high sensitivity, and selectivity for the target hydrogen. The smallest frequency difference detectable in our sensor system including oscillator, mixer, low pass filter, comparator, and field programmable gate array (FPGA) was ≈1 Hz, which is a significant output value that can sufficiently detect hydrogen concentrations below 1 ppm. Compared with pure SnO2, 3D Cu (3%)‐doped SnO2 nanostructure based‐SAW sensor exhibited the highest response to hydrogen gas. The elevated response of the 3D Cu‐doped SnO2 based SAW sensor to hydrogen gas is mainly attributed to the acoustoelectric interaction. Photoluminescence and X‐ray photoelectron spectroscopy analysis divulged that Cu‐doping in SnO2 produces a large number of surface oxygen vacancies, which enhances the hydrogen adsorption on the SnO2 surface, resulting in a significant improvement in the response to hydrogen gas. The sensor characteristics at the system level showed excellent selectivity, repeatability, and long‐term stability to hydrogen gas. The sensing mechanisms (mass loading and acoustoelectric interaction) in the SAW sensor due to hydrogen adsorption have been experimentally investigated and the obtained results are discussed in detail.

Anomalous Hall effect of PdCo alloy thin films to detect low hydrogen concentration in air

The anomalous Hall effect of thin PdCo films (Pd0.8Co0.2 alloy films; 5, 15, and 30 nm thick) subjected to various hydrogen concentrations in the gas phase was investigated. The Hall voltage of the 15 and 30 nm thick PdCo films against an external magnetic field exhibited hysteresis, indicating the anomalous Hall effect of PdCo. The hydrogen absorption in the 5 nm PdCo film decreased the Hall voltage in all considered magnetic fields. Moreover, the slope of the Hall voltage around a zero magnetic field decreased. When N2 was used as the carrier gas, the slope was proportional to the logarithm of the hydrogen concentration. For dry air, the slope differed from and was similar to that for N2 below and above hydrogen concentrations of 0.5% and 1.0%, respectively. The adsorbed oxygen on the PdCo surface disturbed the dissolved hydrogen in PdCo at low hydrogen concentrations in dry air.

Study of the Sensitivity of Porous SnO2-Based Thick-Film Elements to the Hydrogen Concentration in Air

Study of the Sensitivity of Porous SnO2-Based Thick-Film Elements to the Hydrogen Concentration in Air

Investigation on Characteristic of Tritium Oxidation by Natural Soils

A passive catalytic reactor without heating is required to enhance the safety of a fusion facility. A precious metal catalyst without heating is not suitable to oxidize tritium under conditions of low hydrogen concentration and room temperature. In addition, under a moisture condition, tritium oxidation of a precious metal catalyst drops drastically since moisture adsorbs active sites on the surface of the catalyst. Hence, as a method of tritium oxidation under a moisture condition at room temperature, we have focused on bacterial oxidation of tritium by hydrogen-oxidizing bacteria in natural soil to realize a passive reactor. In this study, we investigated the effect of hydrogen concentration on tritium oxidation by hydrogen-oxidizing bacteria in natural soils to understand the characteristic of tritium oxidation by hydrogen-oxidizing bacteria from the viewpoint of engineering. In our experiment, efficiency of tritium oxidation by a natural soil was obtained at room temperature in the range of hydrogen concentration from 0.5 to 10 000 parts per million (ppm) under a moisture condition. The efficiency of tritium oxidation was the highest at a hydrogen concentration of 0.5 ppm, which equals the value of the hydrogen concentration in air. Our results show that hydrogen-oxidizing bacteria could efficiently oxidize tritium with a low concentration of hydrogen, at room temperature, with high moisture. This showed a tendency opposite to a metal catalyst. A bioreactor using hydrogen-oxidizing bacteria complemented a conventional catalytic reactor using a precious metal catalyst since hydrogen-oxidizing bacteria could oxidize tritium efficiently with a low concentration of hydrogen, at room temperature, with high moisture.

Tritium oxidation test by platinum-alumina catalyst under moisture and hydrocarbons atmosphere

To design a detritiation system (DS) applicable to a fire event, it is important to investigate influence of moisture and hydrocarbons produced by combustion of cables in fire on tritium oxidation efficiency of a catalytic reactor. In our experiments, when we assumed that tritium release in a simulated room in the following scenarios as fire situation, (I) tritium only; (II) tritium and excess moisture; (III) tritium and excess hydrocarbons, we conducted demonstration test of tritium oxidation using by DS consist of a catalytic reactor packed with platinum-alumina catalyst and a dryer with molecular sieves. We investigated the detritiation behavior and determined the volume of catalyst to satisfy requirement of tritium oxidation efficiency of a catalytic reactor packed with the catalyst. The tritium concentration theoretically decreased by DS since the tritium oxidation efficiency kept high under the conditions of three scenarios. Our results showed that the concentration of hydrogen in air and temperature of catalyst had an influence on the tritium oxidation efficiency of the catalytic reactor. We determined the worst scenario for tritium oxidation and evaluated the amount of catalyst to meet the requirement of the tritium oxidation efficiency.

Influence on moisture and hydrocarbons on conversion rate of tritium in catalytic reactors of fusion-DEMO detritiation system

ABSTRACTThoughtful consideration of abnormal events such as fire is required to design and qualify a detritiation system (DS) of a nuclear fusion facility. Since conversion of tritium to tritiated vapor over catalyst is the key process of the DS, it is indispensable to evaluate the effect of excess moisture and hydrocarbons produced by combustion of cables on tritium conversion rate considering fire events. We conducted demonstration tests on tritium conversion under the following representative conditions: (I) leakage of tritium, (II) leakage of tritium plus moisture, and (III) leakage of tritium plus hydrocarbons. Detritiation behavior in the simulated room was assessed, and the amount of catalyst to fulfill the requirement on tritium conversion rate was evaluated. The dominant parameters for detritiation are the concentration of hydrogen in air and catalyst temperature. The tritium in the simulated room was decreased for condition (I) following ventilation theory. An initial reduction in conversion rate was measured for condition (II). To recover the reduction smoothly, it is suggested to optimize the power of preheater. An increase in catalyst temperature by heat of reaction of hydrocarbon combustion was evaluated for condition (III). The heat balance of catalytic reactor is a point to be carefully investigated to avoid runaway of catalyst temperature.

Pt–WO3 porous composite ceramics outstanding for sensing low concentrations of hydrogen in air at room temperature

Pt–WO3 porous composite ceramics have been prepared from Pt and WO3 nanoparticles through pressing and sintering. These ceramics exhibit extraordinary room-temperature sensing capabilities, including high sensitivities, fast response and recovery speeds, and good stability, for low concentrations of hydrogen (at and below 1000 ppm) in air; while for high concentrations of hydrogen (above 2000 ppm) in air, the recoveries in air are only partial in given amounts of time. We propose that for low concentrations of hydrogen, the response results from the reaction of hydrogen with chemisorbed oxygen on WO3; while for high concentrations of hydrogen, hydrogen chemisorption on WO3 will occur after all chemisorbed oxygen on WO3 is reacted. The relatively high stability of chemisorbed hydrogen on WO3 is responsible for the observed partial recoveries. Our results show that Pt–WO3 composite ceramics are highly competitive for sensing low concentrations of hydrogen in air at room temperature among various metal oxide semiconductor bulk materials.

Analytical and numerical assessments of local overpressure from hydrogen gas explosions in petrochemical plants

SummaryAccurate prediction of pressure rise is important for safety assessments of a petrochemical plant in the event of an explosion accident. The sudden pressures arising from gas explosions at various hydrogen concentrations in air have been predicted analytically and numerically. These solutions were compared against experimental data. The analytical solution, based on the self‐similar solution for pointwise strong explosions in an open space, which assumed no energy loss and premixed fuel‐air mixture, reasonably predicted the explosive‐ignition detonation case while the numerical solutions were more suitable to model spark‐ignition deflagration cases that accounted for the effect of turbulence arising from three‐dimensionality and presence of obstacles in the computational domain. Comparison of both analytical and numerical results against experimental data indicates that their differences are within a 30% margin. The analytical model presented herein can be useful for field engineers who want conservative estimates of the overpressure resulting from explosive‐ignition detonation. Copyright © 2016 John Wiley & Sons, Ltd.

Characterization and hydrogen gas sensing performance of Al-doped ZnO thin films synthesized by low energy plasma focus device

Nanocrystalline Al-doped ZnO (AZO) thin films were deposited on glass substrates at room temperature by Mather-type plasma focus device using a ZnO target with an Al content of 3 wt%. The effect of number of focus shots on the microstructure, elemental composition, surface morphology and H2 gas sensor performance of AZO deposited thin films were investigated. X-ray diffraction (XRD) analysis confirmed the polycrystalline nature of the all deposited AZO thin films. XRD results also indicated strong dependence of crystallinity and crystallite size of deposited thin films on number of focus shots. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) analyses led to the conclusion that the size of grains/clusters on the surface of thin films and the surface roughness of deposited samples enhance with increasing of focus shots. The experiments and measurements involving the AZO deposited thin films towards hydrogen were carried out at different operating temperatures within 150–400 °C for various concentrations of hydrogen in air. The H2 sensing response enhanced with concentration and operating temperature, and reached its maximum at 300 °C–1000 ppm concentration of hydrogen gas. The results also indicated shorter response times for samples deposited with less focus shots.

Growth, characterization, and investigation of H2 gas sensing performance of Al-doped ZnO thin films synthesized by plasma focus device

This paper reports characterization of Al-doped ZnO (AZO) thin films deposited on glass substrates at room temperature by a low energy (1.3 kJ) plasma focus device using a ZnO target with an Al content of 3wt%. A particular focus of investigation is on properties relevant to the usage of thin films as hydrogen gas sensors. Indeed, the dependence of angular position of substrate on structural, morphological and gas sensing properties of AZO thin films is investigated. The results obtained from X-ray diffraction (XRD) reveal that all the films are of polycrystalline zinc oxide in nature, possessing hexagonal wurtzite structure. Also XRD results indicate strong dependence of crystallinity of deposited thin films on angular position of samples. Scanning electron microscopy and atomic force microscopy results reveal the structure growth and enhancement of surface roughness with decreasing the angle with respect to anode axis. The experiments and measurements involving the AZO deposited thin films towards hydrogen were carried out at different operating temperatures within 150–400 °C for various concentrations of hydrogen in air. The H2 sensing response enhanced with concentration and operating temperature, and reached its maximum at 300 °C to 1000 ppm concentration of hydrogen gas. The results also indicated shorter response times for samples deposited at larger angular positions.

A study on the characteristics of the deflagration of hydrogen-air mixture under the effect of a mesh aluminum alloy

Mesh aluminum alloys (MAAs) have been widely used in military and civilian applications to suppress the explosion of flammable gases (fluids) inside containers. However, MAAs have not been tested in or applied to the hydrogen suppression-explosions. Hence, a typical MAA product, i.e., one that has been in wide use, is selected as the experimental material in the present study. The characteristics of the deflagration of hydrogen-air mixture inside an MAA-filled tube are investigated, and the effects of the filling density of the MAA and the concentration of hydrogen in air on the deflagration are examined. The suppressing effect of the MAA on the deflagration of hydrogen-air mixture is compared with its effect on the deflagration of a typical hydrocarbon fuel in air. The results show that not only is the existing MAA product unable to effectively suppress the deflagration of hydrogen-air mixture, but it also increases the maximum explosion pressure, which is opposite to the satisfactory suppressing effect of the MAA product on the deflagration of hydrocarbon fuels such as methane. The results of this study provide a scientific basis for the effective prevention of explosion accidents with hydrogen and for the development of explosion-suppression products.

Flame instability of lean hydrogen–air mixtures in a smooth open-ended vertical channel

This work addresses the experimental investigation and analytical interpretation of a flame subject to acoustic–parametric instability exited by self-generated pressure pulses. The research presented herein was carried out with lean hydrogen–air mixtures during flame propagation in a smooth channel with an open end. It was found that very lean mixtures with hydrogen concentrations in air of less than 14% vol. H2 generate acoustic oscillations due to flame instabilities, which, in turn, significantly influence the propagation of the flame. Above a 14% vol. H2 concentration in the air, the flame becomes relatively stable with respect to self-generated acoustic perturbations. It was also found that an external polychromatic sound with a dominant frequency of 1000Hz inhibits the instabilities and results in a reduced flame propagation velocity. Numerical solutions of the Searby and Rochwerger analytical formulation for the acoustic–parametric instability were utilized in order to analyze the experiments and study the influence of different parameters on the existence of a spontaneous transition from the acoustic to the parametric instability.

Hydrogen–air deflagrations: Vent sizing correlation for low-strength equipment and buildings

This paper aims to improve prediction capability of the vent sizing correlation presented in the form of functional dependence of the dimensionless deflagration overpressure on the turbulent Bradley number similar to our previous studies. The correlation is essentially upgraded based on recent advancements in understanding and modelling of combustion phenomena relevant to hydrogen–air vented deflagrations and unique large-scale tests carried out by different research groups. The focus is on hydrogen–air deflagrations in low-strength equipment and buildings when the reduced pressure is accepted to be below 0.1 MPa. The combustion phenomena accounted for by the correlation include: turbulence generated by the flame front itself; leading point mechanism stemming from the preferential diffusion of hydrogen in air in stretched flames; growth of the fractal area of the turbulent flame surface; initial turbulence in the flammable mixture; as well as effects of enclosure aspect ratio and presence of obstacles. The correlation is validated against the widest range of experimental conditions available to date (76 experimental points). The validation covers a wide range of test conditions: different shape enclosures of volume up to 120 m3; initially quiescent and turbulent hydrogen–air mixtures; hydrogen concentration in air from 6% to 30% by volume; ignition source location at enclosure centre, near and far from a vent; empty enclosures and enclosures with obstacles.

Hydrogen sensing by sol–gel grown NiO and NiO:Li thin films

Hydrogen sensors have been prepared using nickel oxide (NiO) and lithium-doped nickel oxide (NiO:Li) thin films, deposited on glass substrates by the sol–gel spin coating technique. The surface morphology, structure, optical and electrical properties of the obtained films were studied. Hydrogen sensing results are presented for three operating temperatures (140, 160, and 180°C) and for hydrogen concentrations ranging from 1000 to 15,000ppm in synthetic air. The NiO and NiO:Li (2% and 8% doping concentrations) sensors show maximum responses for the operating temperature of 180°C. When tested at different hydrogen concentrations in air, the lithium-doped NiO sensors showed a higher response than the undoped NiO films.

Experimental investigation on the kinetics of catalytic recombination of hydrogen with oxygen in air

Catalytic recombination of hydrogen with oxygen is one of the most attractive options to control the hydrogen concentration in air. The basic pre-requisite for the process design of any catalytic reactor is the knowledge of kinetic data. In the present study, the kinetic data for the catalytic recombination of hydrogen in presence of 0.5% Pd on alumina catalyst were generated using a packed bed reactor with complete recycle. The experiments were conducted using low concentration of hydrogen in air at different temperatures and the apparent rate constants were estimated assuming a first order reaction with respect to hydrogen. The resistances due to internal and external mass transfer were decoupled from the apparent kinetics and estimated separately. The activation energy and frequency factor were found out using the slope and intercept of the Arrhenius plot. The effect of different process parameters such as temperature, superficial velocity and the catalyst particle size on the overall reaction rate was also studied. The knowledge of the intrinsic kinetics along with the mass transfer can be easily extended for the design of catalytic recombination reactors during scale up.