Decrease In Hydrogen Content Research Articles

Oxygen distribution in bed and safety analysis during hydrogen purification process from oxygen-containing feed gas

In order to analysis the oxygen distribution in the adsorption bed during the hydrogen purification process from oxygen-containing feed gas and the safety of device operation, this article established a non-isothermal model for the pressure swing adsorption (PSA) separation process of 4-component (H2/O2/N2/CH4), and adopted a composite adsorption bed of activated carbon and molecular sieve. In this article, the oxygen distribution in the adsorption bed under different feed gas oxygen contents, different adsorption pressures, and different product hydrogen purity was studied for both vacuuming process and purging process. The study shows that during the process from the end of adsorption to the end of providing purging, the peak value of oxygen concentration in the adsorption bed gradually increases, with the highest value exceeding 30 times the oxygen content of the feed gas. Moreover, the concentration multiplier of oxygen in the adsorption bed increases with the increase of the adsorption pressure, decreases with the increase of the oxygen content in the feed gas, and increases with the decrease of the hydrogen product purity. When the oxygen content in the feed gas reaches 0.3% (vol), the peak value of oxygen concentration in the adsorption bed exceeds 10% (vol), which will make the front part of the oxygen concentration peak fall in an explosion limit range. As the decrease of product hydrogen content, the oxygen concentration peak in the adsorption bed will gradually move forward to the adsorption bed outlet, and even penetrate through the adsorption bed. And during the process of the oxygen concentration peak moving forward, the oxygen will enter the pipeline at the outlet of the adsorption bed, which will make the pipeline space of high-speed gas flow into an explosion range, bringing great risk to the device. The preferred option for safe operation of PSA for hydrogen purification from oxygen-containing feed gas is to deoxygenate the feed gas. When deoxygenation is not available, a lower adsorption pressure and a higher product hydrogen purity (greater than or equal to 99.9% (vol)) can be used to avoid the gas in the adsorption bed outlet pipeline being in the explosion range.

Detonation effect of hydrogen-oxygen mixtures at various initial pressures and hydrogen concentrations in obstructed channels

Numerical investigations have been conducted for the effects of initial ambient pressure, hydrogen concentration, and obstacle distribution on the chemical kinetic characteristics of stable detonation propagation, as well as the changes in the shape and size of detonation cells. The configuration studied is a rectangular channel with regularly spaced obstacles containing the mixture of hydrogen and oxygen. The results indicate that under the same blockage ratio conditions, the position where detonation is generated in the channel with obstacles distributed on one side is farther than in the channel with obstacles distributed on both sides. However, there is no significant change in flame speed or detonation cell size after reaching stable detonation in both cases. The study reveals that under fuel-rich conditions, an increase in hydrogen concentration leads to an increasing duration for the flame to propagate to the end of the channel, accompanied by the distance from the ignition point to the occurrence of detonation also increases. Additionally, under fuel-lean conditions, as the hydrogen concentration decreases, the distance from the ignition point to the occurrence of detonation also increases. The study identifies the limiting concentration for hydrogen detonation is in the range of 18.3 %–60 %. As the initial pressure within the channel decreases, the location of detonation occurrence is farther away from the ignition point. And higher initial ambient pressures make detonation more likely to occur within the channel and the size of stable detonation cells decreases as the initial ambient pressure increases.

The influence of solid solution hydrogen and precipitated hydride on the creep behavior of Zircaloy-4

The effect of hydrogen on the creep rates of Zircaloy-4 claddings especially in the low hydrogen concentration remains largely unexplored while creep is considered a main mechanism for spent nuclear fuel failure along with hydride-induced mechanisms. Here, we study the influence of hydrogen on the creep behavior of low burnup Zircaloy-4 cladding from a microstructural perspective. The creep tests at 450 °C and 120 MPa reveal that specimens with hydrogen contents below the terminal solid solubility for dissolution (TSSD) at the test temperature exhibited decreased creep resistance as hydrogen concentration increased, while those with hydrogen contents above the TSSD demonstrated increased creep resistance with higher hydrogen concentration. The lowest creep resistance occurs at the hydrogen concentration corresponding to the TSSD. Additional microstructural analyses using electron backscattered diffraction (EBSD) show the increasing intra-granular/inter-granular hydride ratio in the post-crept specimens as the hydrogen concentration decreases, suggesting that hydrogen atoms in solid solution aid creep progression. Also, an increased amount of twin boundaries is observed in post-crept specimens with hydrogen concentration above TSSD. These results suggest that creep assessment in spent nuclear fuels may require caution especially in low-burnup regime.

Design and performance optimization of diesel engine waste heat recovery methanol reforming hydrogen generation system

Abstract A shell-and-tube Methanol Steam Reformer (MSR) system was designed for diesel engines. The effects of structural and operational parameters of the spiral baffles in the methanol reformer on heat transfer and hydrogen production performance were investigated. Additionally, a multi-objective optimization using response surface methodology was conducted to study the interactive effects of spacing and thickness, as well as liquid hourly space velocity and steam–methanol ratio, on the methanol conversion rate, hydrogen concentration and hydrogen production. The results indicated that reducing the baffle spacing and increasing the baffle thickness further improved heat transfer efficiency. Optimal conditions were achieved at a spacing of 30 mm and a thickness of 2 mm, resulting in a methanol conversion rate of 64.2 %. Increasing the steam–methanol ratio from 0.5 to 2 increased the methanol conversion rate from 50.6 % to 79.7 %, with a subsequent decrease in hydrogen concentration. Increasing the liquid hourly space velocity from 635 h−1 to 1905 h−1 significantly reduced the methanol conversion rate from 94.5 % to 64.2 %, but the hydrogen production increased from 0.111 mol/s to 0.228 mol/s. Optimization results indicate that the liquid hourly space velocity and steam–methanol ratio have a greater influence on the hydrogen production efficiency of the methanol reformer.

MAIN COMPONENTS OF FOSSIL COALS, THEIR CONSUMER QUALITIES AND HAZARDOUS PROPERTIES OF COAL SEAMS

Purpose: the goal is to more fully disclose the essence of the geological processes of coal formation and improve the regulatory framework for the safe conduct of mining operations to establish correlations or trends in changes in the elemental content of the main components of organic mass and mineral impurities for different states of coal during metamorphic transformations of coal seams. Methodology: the technique involves using carbon content as a criterion for assessing the degree of metamorphism of the transformation of coal seams, since it practically functionally controls the sum of the remaining main components of the organic mass throughout the entire range of coalification. This made it possible to use reliable experimental data from technical and elemental analysis of reference and regulatory documents on the consumer qualities of coal in scientific research, established by standard methods over several decades, to predict the hazardous properties of coal seams. Results: The patterns of changes in the elemental content of the main components of organic mass and mineral impurities for different states of coal samples (analytical, organic, working) during metamorphic transformations of coals have been established. Scientific novelty: Based on the change in the elemental content of the relative organic mass of carbon and hydrogen, as well as the moisture of analytical samples, three characteristic stages of metamorphic transformations of coal seams were established, which determine their dangerous properties. With a carbon content of 79÷89%, the hydrogen content per conventional organic mass remains unchanged, and the transformations at this stage are almost completely associated with the reduction of oxygen in other components of mineral impurities. Individual differences between mine layers at this stage of transformation are associated with the moisture content in analytical samples and the amount of external moisture removed during sample preparation. With a further increase in the influence of metamorphic processes (increase in carbon content to 89÷93%), a decrease in hydrogen content occurs, which indicates the removal of a certain proportion of moisture from the analytical samples together with external moisture from the system. At the third stage of metamorphic transformations of coal seams (carbon content more than 93%), together with external moisture, based on the minimum values of hydrogen and moisture in analytical samples, there was a further reduction in the moisture of analytical samples to their minimum values. Practical value: the research results make it possible to develop proposals for improving the regulatory framework for safe mining operations in terms of predicting the manifestation of hazardous properties of coal seams. Keywords: coal seams, hazardous properties, mining operations, coal, samples, condition, analysis, components, organic mass, mineral impurities, metamorphism, forecast, regulatory framework, safety, improvement.

Composition transformation of terrigenous organic matter resinous-asphaltene components in super-deep wells in Siberia during meso- and apocatagenesis

The evolution of the elemental composition of dispersed organic matter (DOM) heterocyclic components during catagenesis was traced via studying samples from the Tyumen (SG-6) and Srednevylyuy-27 (SV-27) super-deep wells of Siberia. During mesocatagenesis, the composition of terrigenous DOM asphaltenes and resins undergoes directed changes: a decrease in hydrogen and oxygen content, enrichment with carbon, and graphitization of the structure. During apocatagenesis, due to high-temperature destruction, on the one hand, there is a condensation of individual blocks of asphaltenes and their transition to an insoluble form (formation of epiasphaltenic kerogens – EPAK). On the other hand, the lighter part of the asphaltenes goes into the formation of hydrocarbons and gas formation – a relative increase in the concentration of the former in % by mass of residual bitumoids is noted, as well as structural redistributions within benzene and spirit-benzene resins. In all studied parameters of the elemental composition, a symmetrical (unidirectional) transformation of resinous and asphaltene components of bitumoids from the SG-6 and SV-27 wells under harsh thermobaric conditions is noted. The obtained results should be taken into account when predicting new oil and gas accumulation zones in deep-laid horizons.

Decreasing Hydrogen Content within Zirconium Using Au and Pd Nanoparticles as Sacrificial Agents under Pressurized Water at High Temperature.

Decreasing hydride-induced embrittlement of zirconium-based cladding is a significant challenge for the successful dry storage of spent nuclear fuel. Herein, to radically minimize hydride-induced embrittlement, we used nanoparticles as sacrificial agents with a greater affinity than zirconium for hydrogen. Corrosion experiments in the presence of gold (Au) and palladium (Pd) nanoparticles under simulated pressurized water reactor (PWR) conditions revealed that the hydrogen content of the zirconium samples was remarkably reduced, with a maximum decrease efficiency of 53.9% using 65 nm Au and 53.8% using 50 nm Pd nanoparticles. This approach provides an effective strategy for preventing hydride-induced embrittlement of zirconium-based cladding.

Magnetism and equation of states of fcc FeHx at high pressure

Abstract Hydrogen is a strong candidate for light alloying elements in terrestrial cores. Previous first-principles studies on non-stoichiometric hexagonal close-packed (hcp) and double hexagonal close-packed (dhcp) FeHx predicted a discontinuous volume expansion across the magnetic phase transition from non-magnetic (NM) or antiferromagnetic (AFM) to ferromagnetic (FM) state with increasing the hydrogen content, x at 0 K. However, previous high-pressure and -temperature neutron diffraction experiments on face-centered cubic (fcc) FeHx did not reveal such nonlinearity. The discrepancy between theory and experiment may be due to differences in the crystal structure, magnetism, or temperature. In this study, we computed the equation of states for fcc FeHx using the Korringa-Kohn-Rostoker method combined with the coherent potential approximation (KKR-CPA). In addition to the four types of ground-state magnetism (FM, AFM-I, AFM-II, and NM), we calculated the local magnetic disorder (LMD) state, which approximates the paramagnetic (PM) state with local spin moment above the Curie temperature. Our results show that even though FM, AFM-I, AFM-II, and NM calculations predict a discontinuity in the volume at 0 K, the volume becomes continuous above the Curie temperature, consistent with the previous neutron experiment. From the enthalpy comparison at 0 K, FM fcc FeH (x = 1) becomes the NM state above ~48 GPa. The magnetic transition pressure decreases with decreasing hydrogen content. Therefore, below the magnetic transition pressure, local spin moments affect the density and elastic wave velocity of fcc FeHx, which may be important for small terrestrial bodies such as Mercury and Ganymede. By contrast, at the Earth’s core pressure above 135 GPa, fcc FeHx becomes NM. Thus, we calculated the density and bulk sound velocity as a function of pressure at 0 K for NM fcc FeHx. The density at 360 GPa decreases with increasing hydrogen content, with FeH0.5 best matching the preliminary reference Earth model (PREM) of the inner core. Since the density decreases with increasing temperature, this value constrains the upper limit of hydrogen content, assuming that the inner core is fcc FeHx. On the other hand, the bulk sound velocity at 360 GPa increases with increasing hydrogen content, with FeH0.3 best matching the PREM, which may give a lower bound. Assuming that Poisson’s ratio of the FeHx alloy is equal to that of the inner core, we examined the effects of temperature on density and bulk sound velocity. The results suggest that the fcc FeHx alloy alone cannot explain the inner core density and bulk sound velocity simultaneously unless the temperature is extremely low (T < 4000 K).

Effect of Quaternary Ammonium Salts and 1,2,4-Triazole Derivatives on Hydrogen Absorption by Mild Steel in Hydrochloric Acid Solution.

The treatment of low-carbon steel items with hydrochloric acid solutions is used in many industrial technologies. This process is accompanied not only by metal corrosion losses, but also by hydrogen absorption by the metal. In this study, the kinetics of hydrogen cathodic reduction on low-carbon steel in 2 M HCl containing corrosion inhibitors, namely, quaternary ammonium salts and a 3-substituted 1,2,4-triazole, have been studied. Adsorption isotherms of corrosion inhibitors on cathodically polarized steel surface have been obtained. XPS data provide valuable information on the composition and structure of protective layers formed on steel in HCl solutions containing inhibitors. The main rate constants of the stages of gaseous hydrogen evolution and incorporation of hydrogen atoms into the metal have been determined. The addition of quaternary ammonium salts or 3-substituted 1,2,4-triazole inhibits the cathodic reduction of hydrogen and its penetration into steel in the HCl solution. 3-substituted 1,2,4-triazole is the most efficient inhibitor of hydrogen absorption. The inhibitory effect of this compound is caused by a decrease in the ratio of the hydrogen concentration in the metal phase to the degree of surface coverage with hydrogen. The maximum decrease in hydrogen concentration in the metal bulk in the presence of the 3-substituted 1,2,4-triazole is 8.2-fold, which determines the preservation of the plastic properties of steel as it corrodes in HCl solutions. The high efficiency of the 3-substituted 1,2,4-triazole as an inhibitor of hydrogen cathodic reduction and absorption results from strong (chemical) adsorption of this compound on the steel surface and the formation of a polymolecular protective layer.

Lewis number effects on laminar and turbulent expanding flames of NH3/H2/air mixtures at elevated pressures

This study clarifies the effects of Lewis number (Le) on laminar and turbulent expanding flames of NH3/H2/air mixtures. The laminar burning velocity (SL) and turbulent burning velocity (ST) were measured using a medium-scale, fan-stirred combustion chamber with ammonia/hydrogen molar ratio (NH3/H2) of 50/50 and 80/20 under the maximum pressures of 5 atm. The lean laminar flame with NH3/H2 = 50/50 is significantly accelerated by the diffusional–thermal instability, which dominated the trend of ST,c=0.1 with the equivalence ratio (ϕ). The lean normalized turbulent burning velocity (ST/SL) increases with the decrease of hydrogen content due to the weakening effects of SL. However, the ST/SL reaches peak with hydrogen volumetric content less than 20% due to effects made by diffusional–thermal instability than SL did. The turbulent flame of NH3/H2/air mixtures is characterized by self-similar acceleration propagation, and propagation with Le < 1 is faster. A modified correlation considering the effects of Le was proposed, as (d<r>/dt)/σSL = 0.118(ReT,flameLe−2)0.57, which was able to predict not only the self-similar propagation of NH3/H2/air but also the previous syngas/air flames. The Kobayashi correlations modified by three kinds of Le power exponents were used to clarify the effects of Le by comparing their fitting parameters and predictive powers on experimental data and literature data. Similar pre-factors, power exponents and the goodness of fit (R2) were obtained with Le ranging from 0.58 to 1.62, which suggested that the determination of Le power exponent had no significant effect on the prediction accuracy of the ST/SL trend with data of Le near unity. This might be attributed to the fact that the variation ranges of the dimensionless number that characterizes the experimental conditions is much larger than that of the Le.

Analytical methods for the effect of anode nitrogen concentration on performance and voltage consistency of proton exchange membrane fuel cell stack

Buckets effect remains one of the most important factors limiting the fuel cell stack performance and lifetime. An experiment on a 16-cell stack with decreasing hydrogen concentration is conducted to investigate the effect of anode nitrogen concentration on stack performance and voltage consistency. The mean voltage decay rate of the stack is only 6% at the current density of 1.0 A cm−2, but the decay rate of the single cell with minimum voltage reaches up to 18%. The voltage standard deviation of the fuel cell stack increases by about 8 mV with the decrease in hydrogen concentration from 100% to 85%. Results show that the local voltage standard deviation is as high as 30 mV at 85% hydrogen concentration when the 16 cells are divided into four groups. The influence of local voltage consistency on the overall voltage consistency is further studied. The local voltage consistency can be served as a reliable indicator of anode purge strategy. Moreover, the uneven gas distribution amongst the cells in the stack can be analyzed and effectively detected, according to the local voltage consistency analysis with the experiment of anode nitrogen doping.

Surface Coordination Decouples Hydrogenation Catalysis on Supported Metal Catalysts

Surface Coordination Decouples Hydrogenation Catalysis on Supported Metal Catalysts

Breaking the continuous hydride network in hydrogen-charged pure titanium to repair hydride–induced performance degradation by applying a pulsed electric current

Titanium readily reacts with hydrogen to form hydrides, which greatly deteriorates their mechanical properties. In particular, the continuous hydride network provides a path for crack initiation and propagation. In this study, the hydrogen–charged pure titanium with continuous hydride network were treated by electropulsing treatment and traditional heat treatment. It was found that the elongation of the hydrogen–charged pure titanium were effectively repaired after the electropulsing treatment, while the heat treatment failed. The recovery of elongation of the hydrogen–charged pure titanium can be attributed to the disintegration of the continuous hydride network and the decrease of hydrogen content after the electropulsing treatment. Due to the different electrical properties of the hydrides and the Ti-matrix, the current in hydrogen-charged pure titanium is not uniformly distributed, resulting in the decomposition of the continuous hydride network at lower than conventional tempering temperatures. This particular method can not only be used for the repair of hydride–induced embrittlement, but also can be extended to the optimization of thermo–hydrogen treatment of titanium alloys and the rapid hydrogen release of metal–hydride hydrogen storage materials.

Effect of Pyrolysis Temperature and Wood Species on the Properties of Biochar Pellets

Thermal treatments such as torrefaction and fast pyrolysis are commonly employed methods to produce biofuels with high-energetic properties. In this study, wood chips were heat-treated at different temperatures of torrefaction (315 °C) and fast pyrolysis (400 and 454 °C) to form energetic pellets. Three softwoods, jack pine (JP), balsam fir (BF), and black spruce (BS), were evaluated. Pellets are produced using 20% moisture content and 15% pyrolytic lignin as a binder. Untreated- and treated-wood residues were characterized by surface chemistry, elemental analysis, and chemical composition, whereas all pellets were characterized in terms of density, high heat value (HHV), and durability. Results showed that both thermal treatments caused significant changes in the physicochemical structure of wood residues. Using temperatures higher than 315 °C leads to the disappearance of hydroxyl groups, a decrease in oxygen and hydrogen contents, and an increase in carbon content. Regardless of the treatment temperature, pellets made from heat-treated JP had the best durability (93%). In contrast, the calorific values of wood-treated pellets reached up to 31 MJ/kg, compared to untreated-wood pellets (19 MJ/kg). Thus, the densification of the thermal-treated wood residues represents a potential approach for producing biofuels with high energetic value.

Green hydrogen leaking accidentally from a motor vehicle in confined space: A study on the effectiveness of a ventilation system

Green hydrogen can play a considerable role in helping the world achieve net zero emissions by forming a bridge between the energy sector and transportation. Currently, it is, at the initial phase of development, due to the low demand for hydrogen (H2) fuel for transportation in general. However, an increase in the H2 fuel demand in the future will require high investments in the infrastructure sector. In this regard, parking hydrogen vehicles in residential garages pose a potential safety hazard because of the accidents that could arise from hydrogen leaks. The diffusion of hydrogen in a ventilated garage has been investigated using FLUENT software. This study provides some insight into the hydrogen extraction efficiency of a natural ventilation system. We studied the influence of important ventilation parameters (shape and aspect ratio R of opening ventilation) on hydrogen stratification. First, results show a remarkable efficiency in the case of the square shape. Second, when the aspect ratio R decreases, there is an augmentation in fresh air drawn and hydrogen evacuation which generates the decrease of hydrogen concentration inside the garage and increases the extraction efficiency. Highlights This article develops a hot issue in the context of scarce resources, namely the use of hydrogen as a more environmental-friendly source of energy. Eventual leakage of hydrogen in confined spaces frequented by motor vehicles poses a significant hazard. The flow structure and molar fraction of hydrogen is strongly influenced by ventilation parameters The square shape has the lower concentration values; it presents the highest extraction efficiency. The hydrogen extraction of the transverse rectangular shape (R = 0.5) is more efficient and it presents better results than the others do.

Possibility of false interpretations of hydrogen measurements in ferritic steel after an electrochemical cathodic charging process

In an electrochemical charging process applied before measuring the level of hydrogen in ferritic steels, two different side effects, a decrease in diffusible hydrogen content from steel and the detachment of 2nd phase particles from the steel surface, can occur, even during cathodic charging with a high charging current. Neglecting these side effects-associated with the surface chemistry during the electrochemical charging process can result in a false interpretation of the hydrogen diffusion and trapping behaviors in steel, producing conflicting data. A mechanistic reason for the side effects is provided based on the experimental results.

Poisoning of Ammonia Synthesis Catalyst Considering Off-Design Feed Compositions

Activity of ammonia synthesis catalyst in the Haber-Bosch process is studied for the case of feeding the process with intermittent and impurity containing hydrogen stream from water electrolysis. Hydrogen deficiency due to low availability of renewable energy is offset by increased flow rate of nitrogen, argon, or ammonia, leading to off-design operation of the Haber-Bosch process. Catalyst poisoning by ppm levels of water and oxygen is considered as the main deactivation mechanism and is evaluated with a microkinetic model. Simulation results show that catalyst activity changes considerably with feed gas composition, even at exceptionally low water contents below 10ppm. A decreased hydrogen content always leads to lower poisoning of the catalyst. It is shown that ammonia offers less flexibility to the operation of Haber-Bosch process under fluctuating hydrogen production compared to nitrogen and argon. Transient and significant changes of catalyst activity are expected in electrolysis coupled Haber-Bosch process.

Effect of undissolved Nb carbides on mechanical properties of hydrogen-precharged tempered martensitic steel

Nb carbides have attracted significant attention to enhance the resistance of tempered martensitic (TM) steel to hydrogen embrittlement (HE). However, previous studies have elucidated the role of Nb carbides in HE resistance without categorizing their types (i.e., undissolved and newly precipitated). This study focuses on the effect of “undissolved” Nb carbides on the tensile and fatigue properties of hydrogen-precharged TM steels. It validated the following two factors for the HE resistance of the TM steels containing undissolved Nb carbides: hydrogen-trapping by the carbides and refinement of prior austenite grain. The former factor rarely affected the HE resistance owing to the interfacial incoherency between the undissolved carbides and ferritic matrix. Such results are distinguished from previous studies focusing on the newly precipitated carbides. In contrast, the latter factor contributed significantly to the HE resistance via the decrease in hydrogen contents per unit surface of prior austenite grain boundaries.

Modeling of microporosity formation and hydrogen concentration evolution during solidification of an Al–Si alloy**Project supported by the National Natural Science Foundation of China (Grant No. 51901148), the Fund of the State Key Laboratory of Solidification Processing (Northwestern Polytechnical University), China (Grant No. SKLSP202006), and the State Key Lab of Advanced Metals and Materials (University of Science and Technology Beijing), China

We simulate the evolution of hydrogen concentration and gas pore formation as equiaxed dendrites grow during solidification of a hypoeutectic aluminum–silicon (Al–Si) alloy. The applied lattice Boltzmann-cellular automaton-finite difference model incorporates the physical mechanisms of solute and hydrogen partitioning on the solid/liquid interface, as well as the transports of solute and hydrogen. After the quantitative validation by the simulation of capillary intrusion, the model is utilized to investigate the growth of the equiaxed dendrites and hydrogen porosity formation for an Al–(5 wt.%)Si alloy under different solidification conditions. The simulation data reveal that the gas pores favorably nucleate in the corners surrounded by the nearby dendrite arms. Then, the gas pores grow in a competitive mode. With the cooling rate increasing, the competition among different growing gas pores is found to be hindered, which accordingly increases the pore number density in the final solidification microstructure. In the late solidification stage, even though the solid fraction is increasing, the mean concentration of hydrogen in the residue melt tends to be constant, corresponding to a dynamic equilibrium state of hydrogen concentration in liquid. As the cooling rate increases or the initial hydrogen concentration decreases, the temperature of gas pore nucleation, the porosity fraction, and the mean porosity size decrease, whilst the mean hydrogen concentration in liquid increases in the late solidification stage. The simulated data present identical trends with the experimental results reported in literature.

Numerical investigation into the low-pressure detection sensor performance of hydrogen gas with variable soft sphere molecular model

Direct Simulation Monte Carlo (DSMC) method is used to simulate the hydrogen detection process with Microscale In-Plane Knudsen Radiometric Actuator (MIKRA). The variable soft sphere (VSS) model is applied to depict molecular diffusion in the gas mixtures that its results are compared with variable soft sphere (VSS) in literature. On the right side of the shuttle arm, the influence of molecular model (VSS and VHS) on the simulation results is small. And the temperature ratio, heat transfer ratio and pressure ratio are highly close to 1. But on the left side of the shuttle arm, the differences are significant resulting from molecular models. Especially, for the heat transfer on the left side of the shuttle arm, heat transfer ratio of VHS model to VSS model is maximally about 4.3. The influence of gas pressures and hydrogen concentrations on the detection performance of MIKRA is also discussed. The decrease of hydrogen concentration and the increase of gas pressure cause the center of the main vortex to move towards the heater arm, and the influence of the gas pressure is more significant. On the other hand, Knudsen force increases with the increase of the hydrogen concentration and its peak value is obtained in a higher gas pressure. For example, the peak value of Knudsen force can be attained for the gas pressure of about 387 Pa in the pure hydrogen domain while in the pure nitrogen domain, the gas pressure of about 260 Pa. Simultaneously, the relation of the linear dependence of Knudsen force on the hydrogen concentration is proposed to detect hydrogen concentration in N2–H2 mixtures.