Effect Of Gas Pressure Research Articles

From a Co-Mo precursor to 1H and 1T Co-promoted MoS2: exploring the effects of gas pressure

The work presented in this paper makes use of the high-pressure in situ imaging capabilities of the ReactorSTM to demonstrate that single layer 1T Co-promoted MoS2 can be directly synthesized without the use of any intercalating agents by applying highly reducing conditions during the growth. In this work, we have sulfided a CoMo nanoparticle precursor supported on Au(111) using a H2:CH3SH gas mixture at 1 bar and imaged the crystallization process in situ using the ReactorSTM. We have observed that at low temperatures (∼500 K), an intermediate disordered CoMoSx phase is formed which crystallizes into metallic single-layer 1T Co-promoted MoS2 slabs at temperatures close to 600 K. We also show that semiconducting 1H Co-promoted MoS2 slabs synthesized under sulfur-rich conditions using a vacuum physical vapor deposition process, do not transform into their metallic 1T counterparts when exposed to the same reducing gas pressures and temperatures, thus, demonstrating the importance of the highly reducing conditions during the crystallization process for inducing the formation of the metastable 1T phase. XPS spectra of the 1T Co-promoted MoS2 slabs indicate a sulfur deficiency of up to 11% in the top layer S, suggesting the likely role of sulfur vacancies in the formation of the 1T phase.

A Compact Microwave-Driven UV Lamp for Dental Light Curing

The size of current microwave-driven UV lamps limits their direct application in dental light curing. This article proposes a coaxial structure to miniaturize the UV lamp. First, the Drude model and the finite difference time domain algorithm were used to analyze the multi-physical field coupling and the complex field distribution within the lamp. Second, the dimensional parameters of the lamp were optimized, which enabled the lamp to be miniaturized and operate with high performance. Third, to analyze the sensitivity of the lamp, the effects of input power, gas pressure, and gas composition on its performance were investigated. It was found that an input power of 6 watts was enough to light the bulb with over 90% energy utilization. Finally, to verify the feasibility, an experimental system was set up. The lamp was successfully lit in the experiment, and its spectral output was tested. The results show that the microwave-driven UV lamp based on a coaxial structure is miniaturized and broad-spectrum, making it suitable for clinical dental light curing.

Enhanced hydrogen embrittlement of steel by the premature hydrogen dissociation with the increasing inert gas pressure in hydrogen-containing mixtures

Regarding hydrogen embrittlement (HE) in the mixtures of hydrogen and inert gas, the results were understood mainly based on the partial hydrogen gas pressure. On the other hand, the effect of the total gas pressure has not been fully investigated. In this study, fatigue crack growth rate (FCGR) tests were conducted in high-purity hydrogen gas at different gas pressures. Also, the FCGR tests were conducted in hydrogen and nitrogen mixtures at different total gas pressures. The hydrogen partial pressure in the mixture was the same as the high-purity hydrogen. This was the first time that acceleration of the FCGR in the mixtures compared to that in the high-purity hydrogen was observed. To elucidate the mechanism of the enhanced HE in the mixtures, hydrogen permeation and hydrogen desorption experiments were carried out. Based on the results of these tests, the acceleration of the FCGR in the mixtures could be interpreted by the fast hydrogen entry rate, which may result in a higher local hydrogen concentration near the crack tip during a limited time. Density functional theory (DFT) calculations were performed to consider the total gas pressure effect on an atomic scale. The thrust force of other gas molecules in the mixtures made the hydrogen molecules enter the potential field of the iron surface sooner, advancing the dissociation of the hydrogen. This will increase the surface concentration of the hydrogen atoms.

Molecular analysis of hydrogen-propane hydrate formation mechanism and its influencing factors for hydrogen storage

Combining hydrogen and propane, which acts as a thermodynamic additive, to form hydrates is a promising hydrogen storage method. However, the mechanism of hydrate formation, which is the core of hydrate-based hydrogen storage, remains obscure. In this study, the effects of gas composition, pressure, and temperature on hydrogen–propane hydrate formation kinetics were investigated through molecular dynamics simulations. A hydrogen fraction (Xh) in the range of 0.47–0.67 was optimal for forming hydrate cages, whereas for Xh ≤ 0.37 and Xh ≥ 0.77, propane or hydrogen bubbles formed, which inhibited hydrate formation. Within the simulated pressure range, the number of hydrate cages increased with the increasing pressure. However, the analyzed self-diffusion coefficients suggested that the effect of pressure on the hydrate formation kinetics gradually weakened as the pressure increased up to a certain value. Within the simulated temperature range, the number of hydrate cages increased with temperature up to a point below the hydrogen–propane hydrate phase-equilibrium temperature. This result can be attributed to the increase in the self-diffusion coefficients of hydrogen and propane with the increasing temperature. These results provide valuable microscopic insights into the hydrogen–propane hydrate formation mechanism for hydrate-based hydrogen storage and will be useful in experimental research.

Dimensional analysis on microscale gas breakdown with electric field nonuniformity and positive space charge effects

A dimensional method was employed to evaluate the microscale gas breakdown characteristics at atmospheric pressure, resulting in a universal breakdown curve applicable to different types of gases (e.g., Ar, Xe, Ne, and N2). As the gap distance decreases, the breakdown mode transitions from ion-induced secondary electron emission to the field emission regime. In the field emission regime, the positive space charge effect becomes more significant. We discovered that incorporating the positive space charge effect in the field emission regime can be achieved by modifying the local electric field enhancement factor β. Consequently, we propose an effective electric field enhancement factor, βeff, which scales linearly with β, to accurately reproduce the breakdown curve while considering the positive space charge effect. This proposed approach significantly simplifies the numerical model. Additionally, we examined the effects of gas pressure, gap distance, cathode properties (e.g., work function and secondary electron emission coefficient), and electric field nonuniformity.

Effect of gas pressure on microstructure and mechanical properties of TC11 titanium alloy during supersonic fine particle bombardment

The surface nanocrystallization of a Ti–6.5Al–3.5Mo–1.5Zr–0.3Si (TC11) titanium alloy with a lamellar microstructure was carried out by supersonic fine particle bombardment (SFPB). The effect of SFPB gas pressure on its surface integrity, microstructural evolution and mechanical properties was systematically investigated. The results showed that gradient nanostructures on the surface of the TC11 alloy were successfully created after SFPB with different gas pressures. The grain size of the surface’s lamellar microstructure was completely refined to the nanometer scale. And the grain size of nanocrystals decreased with the increase of gas pressure. Meanwhile, the subsurface retained initial lamellar microstructure morphology. Surface roughness was minimized after SFPB with a gas pressure of 1.0 MPa, while microcrack formed at a higher gas pressure of 1.5 MPa, resulting in a decrease of compressive residual stress. With the increase of SFPB gas pressure, the surface microhardness and the depth of hardened layer gradually increased, and yield strength and tensile strength was improved. Nevertheless, the elongation was not greatly changed. The fracture morphology changed from typical ductile fracture to quasi-cleavage and ductile mixed fracture.

Effects of Membrane Thickness, Gas Pressure and Electron Dose in Gas Cell Transmission Electron Microscopy.

Effects of Membrane Thickness, Gas Pressure and Electron Dose in Gas Cell Transmission Electron Microscopy.

Fast simulation of the E–H mode transition in Ar/O2 inductively coupled plasmas

In this work, an analytical hybrid model, which consists of an analytical electromagnetic model and a global model, is developed to investigate the E to H mode transition in a planer inductively coupled plasma. By employing the hybrid model, the effect of discharge frequency, oxygen content, and gas pressure on the E to H mode transition is investigated. The results show that the electron density increases rapidly with coil current when the discharge shifts to the H mode, and the mode transition becomes smoother and occurs at lower current when the driving frequency is higher. As oxygen content increases, the electron density declines, and the threshold current for the mode transition exhibits a rising trend. The evolution of the threshold current with pressure is nonlinear; i.e., it decreases first and then increases, and the minimum value varies with discharge frequency. In addition, the plasma composition also changes during the E to H mode transition; i.e., all the charged species densities increase with coil current, except the O− density, which varies nonlinearly, and this indicates the decreasing electronegativity in the H mode. The results obtained in this work are helpful for understanding the effect of different discharAr/O2ge parameters on the E to H mode transition in Ar/O2 inductive discharges.

Experimental study of the effects of gas pressure and resonator length on the CO2 laser pulse shape

در این مقاله، به بررسی اثر پارامترهای گوناگون بر شکل تپ‌های گسیلی لیزر 2CO تپی پرداخته شده است. در این راستا، عوامل مختلفی مانند: فشار گاز و هم‌­چنین طول تشدیدگر تغییر داده شدند و شکل تپ‌های گسیلی لیزر در هر حالت به‌همراه اندازه انرژی آن‌ها ثبت گردیدند. نتایج نشان می‌­دهد که انرژی گسیلی با افزایش فشار گاز، به‌شدت افزایش می‌یابد، به‌گونه‌ای که با 2 برابر و 3 برابر شدن فشار، انرژی گسیلی به 3 و 5 برابر، پهنای زمانی تپ‌ها به نیم و یک‌سوم و زمان برساخت آن‌­ها نیز به 9/0 و 7/0 اندازه‌های اولیه‌ی خود می‌رسند. هم‌­چنین با درازتر شدن طول کاواک، از دیرش زمانی میخه و به‌ویژه دنباله‌ی تپ‌ها کاسته می‌گردد. برای انجام این رشته آزمایش‌ها، از یک لیزر دست‌ساز با فشار کار در بازه‌ی atm 1-3 بهره گرفته شده است.

THE PROBLEM OF LIQUEFACTION OF NATURAL GAS CONTAINING NITROGEN IN SMALL-SCALE PLANTS

One of the problems in the implementation of natural gas liquefaction technology in a closed high-pressure cycle is the accumulation of low-boiling components, in particular, nitrogen in the circulating gas stream, as a result of which the throttle effect decreases and, accordingly, the specific energy consumption of the liquefaction plant increases. The nitrogen concentration influence on the liquefaction plant operation in the throttle cycle of high-pressure natural gas with a nitrogen content of 0 to 6 % was studied using the GazCondNafta software system for computer simulation of technological processes. To solve the problem of liquefaction of nitrogen-containing gases, a liquefaction scheme with two stages of throttling and intermediate separation with nitrogen vapor stripping is proposed. The effect of gas pressure in the nitrogen separator was determined from the point of view of minimizing losses of the main component of natural gas — methane — with stripping gas with a relatively small decrease in energy efficiency. Bibl. 14, Fig. 6, Tab. 4.

Line intensity calculation of laser-induced breakdown spectroscopy during plasma expansion in nonlocal thermodynamic equilibrium.

We present a new, to the best of our knowledge, simulation method for laser-induced breakdown spectroscopy during the plasma expansion phase in nonlocal thermodynamic equilibrium. Our method uses the particle-in-cell/Monte Carlo collision model to calculate dynamic processes and line intensity of nonequilibrium laser-induced plasma (LIP) in the afterglow phase. The effects of ambient gas pressure and type on LIP evolution are investigated. This simulation provides an added way to understand the nonequilibrium processes in more detail than the current fluid and collision radiation models. Our simulation results are compared with experimental and SimulatedLIBS package results and show good agreement.

Effect of Pore Pressure on Strain Rate-Dependency of Coal

Viscoelastic strain rate-dependent behaviour of coal is critical in several subsurface engineering applications especially coal seams gas production. Such rate dependency is controlled by the interaction between coal bulk and gas sorption (a sorbing gas) or gas pressure (a non-sorbing gas). Despite the research conducted to date, the gas pressure effect (non-sorbing) on the viscous behaviour of sediments in particular coal remains unexplored. We, therefore, investigate the strain rate-dependent mechanical behaviour of coal under isotropic loading to specifically explore the effect of gas pressure (Helium) on its rate dependency eliminating the sorption effect. We perform a set of triaxial experiments on coal specimens at dry and pressurised gas (Helium) conditions under different strain rates under isotropic loading. The experimental results show that all coal specimens have viscoelastic strain rate dependency at a dry condition where viscous effect increases with strain rate. As a result, the bulk modulus of the specimens increases with the increase in strain rates. This strain rate dependency response, however, reduces with an increase in pore pressure and vanishes at a certain pore pressure under the same effective stress to that of dry specimens. We further employ X-ray micro-Computed Tomography (XRCT) to 3D scan a coal specimen saturated with Krypton gas undergoing different loading rates to shed light on the micro-mechanisms of gas pressure effect on specimens’ rate dependency. The XRCT results show that gas can be trapped in small-scale fractures and pores during the loading process leading to a localised undrained response that can stiffen the specimen and reduce its ability to show viscous rate dependency. The obtained results are significant in optimizing coal seam gas production and coal seam gas drainage applications.

Hydropneumatic suspension testing of a wheeled armoured personnel carrier

The purpose of this study was to determine the effect of gas pressure and temperature on the spring characteristic of a HP strut used in a wheeled armoured personnel carrier. The research was performed based on a simulation model. Data to validate the model were obtained during experimental tests. The results indicate, among other things, that the friction generated in the seals is an important source of resistance force. Comparison of the simulation results with the measured characteristics indicates a proper modelling of the strut operation. Simulation studies have indicated that it is easy to modify the required suspension parameters by adjusting the initial gas pressure. A linear effect of pressure on static deflection can be assumed. Temperature has a strong influence on the spring characteristic. When it changes, significant changes in vehicle height are observed due to the lack of a compensation system. The temperature changes are not only due to changes in ambient temperature, but also by intense heating of the HP struts caused by the vehicle moving over rough terrain.

An Experimental Study on Novel Gas Discharge Tubes With Graphene as Electron Emission Material

Electrical equipment is subjected to gas discharge tube (GDT) direct current (dc) breakdown voltage dispersion and breakdown voltage drop after a surge. It is noteworthy that GDT damage may even cause the failure of electrical equipment. Accordingly, the chemical vapor deposition (CVD) of graphene was proposed in this study as an electron emission material of the GDT based on the existing electron powder GDT. The GDT exhibiting a voltage class of 470 V was prepared, and its structure and surge characteristics were analyzed. The effects of gas pressure, aging time, and ambient temperature on the breakdown voltage of the graphene GDT were studied. The surge process of the graphene GDT was simulated using the 8/ <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$20~\mu \text{s}$ </tex-math></inline-formula> impulse current generator, and the resistance ability of the graphene GDT against the surge was examined. Moreover, it was compared with the same type of commercial electron powder GDT. As indicated by the experimental results, a positive correlation was identified between the gas pressure and the dc breakdown voltage of the graphene GDT under a certain pressure. The effect of aging time and ambient temperature on dc breakdown voltage was limited. The breakdown voltage of the graphene GDT was first increased and then decreased with the increase in the number of surges. After 100 surges, the breakdown voltage of the graphene GDT stabilized at 350 V, whose stability was better than that of the electron powder GDT. The above-described analysis confirmed that graphene GDT exhibits better surge resistance ability.

Partial discharge induced decomposition and by-products generation properties of HFO-1234ze(E)/CO2: a new eco-friendly gas insulating medium

HFO-1234ze(E) is introduced as a new eco-friendly insulating gas for medium-voltage gas-insulated equipment (MV-GIE). However, there are few reports on the partial discharge (PD) induced decomposition and gaseous, solid by-product generation characteristics of HFO-1234ze(E)/CO2. Herein, the PD decomposition characteristics of HFO-1234ze(E)/CO2 were explored based on a needle-plate electrode that simulates the metal protrusion defect in MV-GIE. The partial discharge inception voltage, and phase-resolved partial discharge of HFO-1234ze(E)/CO2 under different mixing ratios, PD intensity and duration time at 0.15 MPa were obtained. Meanwhile, the PD-induced decomposition and generation of gaseous, solid by-products of HFO-1234ze(E)/CO2 were analyzed. A three-zone pattern that describes the gas–solid metal interface interaction was proposed for the first time. It is found that the increase of HFO-1234ze(E) content brings superior insulation performance, while the precipitation of gaseous (CF4, C2F6, CHF3, C3HF7) and solid by-products gradually aggravated. In order to avoid the negative impact of PD-induced decomposition on the insulation and service life of MV-GIE, the optimal HFO-1234ze(E) content of 30% is recommended. Based on the optimal mixing ratio (30% HFO-1234ze(E)/70% CO2), the effect of gas pressure and electrode materials on solid precipitation, breakdown voltage was also explored. This work guides the development of HFO-1234ze(E) based MV-GIE and understanding the solid by-products precipitation mechanism of eco-friendly insulating gas.

Investigation on the Fragmentation and Outburst Mechanism of Coal Sample with Pore Gas Using CDEM

In this paper, using the continuum-discontinuum element method (CDEM), the fragmentation and outburst process of coal specimen are simulated, and the main factors affecting coal breaking and outburst are explored. The results show that after the coal seam is uncovered, coal generates obvious failure and outburst trend. Near coal-free surface, the fracture coal blocks generate significant displacement, resulting in larger opening widths of coal cracks. Coal deep generates the cracks without an obvious opening width. The crack density of coal with pore gas is larger than those of coal without gas, and it is larger than those of coal without pores. However, in the early stage of coal failure, the obvious separation and outburst ranges of coal with gas are smaller than those of coal without gas, and are smaller than those of coal without pores. The numbers of fracture coal blocks show an increase with the growth of in situ stress, pore ratio and gas pressure. The effect of in situ stress on fracture coal block number (517–10,203) is larger than the effect (7589–15,170) of pore ratio and is larger than the effect (5803–6836) of gas pressure. The effect of in situ stress on a maximum size (0.0387–0.138 m) of fracture blocks is larger than the effect (0.0342–0.0733 m) of pore ratio and is larger than the effect (0.0454–0.0578 m) of gas pressure. The coal outburst velocity and range show an increase with the growth of gas pressure and in situ stress (3.77–5.65 m/s); however, the coal outburst shows a slow decrease with a growth of pore ratio. The effect of gas pressure on the coal outburst velocity (11.51–21.9 m/s) is larger than the effect (3.77–5.65 m/s) of in situ stress and is larger than the effect (4.52–5.23 m/s) of pore ratio. This investigation is beneficial to understand the mechanisms of coal–gas outburst in coal mining and roadway excavation.

Understanding the effect of ambient gas pressure on the nanoparticle formation in electrically exploding wires

In this paper, a computational model characterizing the preparation of metallic nanoparticles by electrically exploding wires from the onset of current flowing through the wire to the final moment of nanoparticle formation in a gaseous environment is constructed. The computational model consists of a 1D magnetohydrodynamic model, a simplified magnetohydrodynamic model with two-temperature approximation, and a set of general dynamic equations based on the nodal approach, corresponding to the phase transition stage, plasma evolution stage, and nanoparticle growth stage, respectively. The numerical investigation on the formation of nanoparticles is performed with “cold-start” conditions. The computational predictions for the dependence of nanoparticle size on proportion under argon gas pressure of 10 kPa demonstrate that the nanoparticles of 21 nm in diameter account for the maximum proportion of 4.3%. It coincides with the experimental measurements for nanoparticles of 19 nm in diameter with the maximum proportion of 3.5%. The computational model is employed to reveal the influence of ambient gas pressures on the process of nanoparticle formation. The variation trends for parameters of exploding products, cooling rate, and nanoparticle diameter with the largest proportion on ambient gas pressures are discussed. The size distribution of nanoparticles under different argon gas pressures matches relatively well with relevant experimental data. This computational model bridges the gap between the electrically exploding wires and the growth of nanoparticles, providing theoretical support for the regulation and control technology in nanoparticle synthesization by electrically exploding wires.

The effect of background argon gas pressure on parameters of plasma produced by Dc- glow discharge

Non-thermal plasmas have become popular as plasma technology has advanced in various fields, including waste management, aerospace technology, and medicinal applications. They can be used to replace combustion fuels in stationary hall motors and need little effort to keep running for longer periods of time. To improve overall system performance, non-reactive gases such as )Xe, Ar, and Kr) are utilized in pure or mixed form to generate plasma. Since DC glow discharge is a fundamental topic of importance, these gases have been researched. The paper concentrates on 2-D modeling and simulation. DC glow-discharge tubes are utilized with argon gas to create plasma and learn about its properties. The magnitude of the electron density, increases with rising pressure, whilst the rest of the parameters gradually decrease with increasing pressure

Experimental investigations on effects of gas pressure on mechanical behaviors and failure characteristic of coals

The mechanical behavior of coal is the key factor affecting underground coal mining and coalbed methane extraction. In this study, triaxial compression and seepage tests were carried out on coal at different gas pressures. The mechanical properties and failure process of coal were studied, as well as the acoustic emission (AE) and strain energy. The influence of gas pressure on the mechanical parameters of this coal was analyzed. Based on the conventional energy calculation formula, the pore pressure was introduced through the effective stress formula, and each energy component of coal containing gas was refined innovatively. The contribution of gas pressure to the total energy input and dissipation during loading was quantitatively described. Finally, the influence of gas pressure on coal strength was theoretically analyzed from the perspectives of Mohr–Coulomb criterion and fracture mechanics. The results show that the total absorbed energy comprises the absorbed energy in the axial pressure direction (positive) and in the confining pressure direction (negative), as well as that induced by the pore pressure (initially negative and then positive). The absorbed energy in the axial pressure direction accounts for the main proportion of the total energy absorbed by coal. The quiet period of AE in the initial stage shortens, and AE activity increases during the pre-peak stage under high gas pressure. The fractal characteristics of AE in three stages are studied using the correlation dimension. The AE process has different forms of self-similarity in various deformation stages.

Experimental study on transient heat transfer characteristics during the dropping of containment pressure

The reactor containment integrity and the pressure inside the containment are the most concern in the practical running process. To evaluate the transient heat transfer, non-equilibrium fraction (NEF) is proposed to represent the completed degree of transient condensation. An empirical correlation for NEF is developed and the fit error is within ±25% for 97% of results. Based on this, a simplified calculation model for transient heat transfer rate is also developed, then the transient condensation heat transfer coefficient (HTC) is obtained to characterize the intensity of transient heat transfer. The effect of mixed gas pressure, air mass fraction and temperature of cooling water on NEF and transient condensation HTC are discussed. The result indicates that the initial air mass fraction and initial gas-mixture pressure play an important role in transient-state heat transfer, and the influence of initial cooling water temperature can be ignored. This study aims to improve the understanding of transient-state heat transfer and provide guidance to practical engineering.