Effect Of Gas Pressure Research Articles

Dynamics of angularly colliding laser-produced plasmas in air and argon ambient

The effects of ambient gas pressure on the dynamics of angularly colliding laser-produced plasmas are investigated in air and Ar ambient. Fast formation of intense stagnation region is observed even in the low-pressure regime, and the tendency of interpenetration is also greater because of the involvement of the fast forward expansion velocity of seed plasmas. An intense and spherical stagnation region is observed at an intermediate pressure regime of Ar ambient. At higher pressure regime, shock front interaction in air ambient and at 10−1 mbar of Ar ambient is due to the regular reflection of shock waves. At 1 mbar of Ar ambient, a channel is formed at the collision front, and its width increases with time which is due to the Mach reflection of shock waves. Increasing inter-plume separation or the increase of angle between the targets significantly influences the shock wave reflections. Mach reflection of shock waves is observed even at 10−1 mbar of Ar ambient in higher angular separation. A peculiar plume splitting is also observed at 750 ns in 10−1 mbar of Ar ambient. Optical emission spectroscopic analysis was also done to understand the spectral emission from interaction region and its variation with ambient gas pressure.

Numerical modelling of coal and gas outburst initiation using energy balance principles

Coal and gas outburst is a common mining hazard as it cannot be readily predicted due to complex processes controlling its occurrence. Understanding these complex processes such as gas flow, mechanical properties and behaviour, stress regimes, and geological structures, is required to enable mitigating the outbursts. The most current thresholds proposed for outburst prediction are empirically based thus ignoring the physical processes involved. While numerical modelling is a powerful tool to simulate the involved physical mechanism in coal and gas outbursts, the use of thresholds for outburst initiation in numerical models has not attracted enough attention to date. In this study, the law of conservation of energy is used to determine the moment of the outburst occurrence; the energy of which is obtained through numerical simulation. Different sources of energy including elastic energy and, free and desorbed gas energies linked to the complex physical processes are modelled and discussed. Different mechanical properties of coal are assigned to discuss the distinction of energy values between normal coal and coal affected by geological structures (known as deformed coal). A 30 m long roadway excavation that penetrates through both normal and deformed coals is simulated to assess the effect of induced stress on outburst initiation during roadway development. In addition, the effects of initial gas pressure and damaged area on the propensity of outburst events are analysed. The numerical model can successfully simulate gas outbursts caused by deformed coal, which poses a higher outburst risk. In addition, the modelling results demonstrate that by increasing the gas pressure in the coal seam, outburst happens in the earlier stages of the roadway development, and more intense outburst can be expected.

Numerical simulation on flow and reaction characteristics for catalytic region in helium-heated steam reformer coupled with HTR-10

In this paper, one dimension steady-state and pseudo-homogeneous model of the hydrogen production reformer in the steam methane reforming (SMR) process using the high temperature gas-cooled test reactor of 10 MW (HTR-10) as heat source (HTR-10/SMR) is simulated based on the semi-coupled solution method using matlab2016b. Firstly, The axial variations of hydrogen production performance including temperature (T2), methane conversion rate (XCH4), carbon monoxide conversion rate (XCO) and hydrogen production per mole methane (YH2/CH4 or total hydrogen production (YtH2)) as well as thermal efficiency (η) are investigated. Then, it is noted that YH2/CH4 decreases from 2.92 mol H2/mol CH4 to 2.53 mol H2/mol CH4. However, YtH2 increases from 2.33 kmol/h to 3.23 kmol/h with the increase of the inlet process gas flow rate (F2inlet) from 4 kmol/h to 6 kmol/h. Finally, YtH2 increases with steam to carbon ratio (S) when S < 4 and decreases when S > 4. The maximum value of YtH2 with 3.03 kmol/h is obtained at S = 4. Especially, XCH4, XCO, YH2/CH4 and η are in the range of 70.54%–90.78%, 38.56%–54.30%, 2.50–3.07 mol/mol CH4 and 54.55%–64.57%, respectively, when T3_inlet is in the range of 850–950 °C. The effect of the process gas temperature and pressure on the system performance can be neglected.

Origin of high-frequency magnetic loss of Y3Fe5O12 single crystal thin films prepared with high-throughput screening by magnetron sputtering

In this study, yttrium iron garnet (Y3Fe5O12, YIG) single crystal nanofilms were deposited at room temperature on a Gd3Ga5O12 (GGG) (111) substrate via magnetron sputtering and ex situ annealing. A high-throughput method was used to systematically study the effects of sputtering gas pressure, sputtering power, and annealing temperature on the microstructure, ferromagnetic resonance signal, and high-frequency magnetic loss. The YIG films fabricated at an Argon pressure of 3 Pa, a sputtering power of 95 W, and an annealing temperature of 800 °C possessed the highest saturation magnetization and lowest linewidth (13.6 Oe). Furthermore, the maximum value of permeability (μ′) was 25.54 under an applied field Hex = 30 Oe of the YIG/GGG (111) film for the first time. In addition, the sources of the high-frequency magnetic loss in the YIG film were investigated. In detail, the roughness, thickness, and polycrystalline structure, along with the existence of oxygen vacancies and anisotropic fields, influenced the linewidth of the film. This study provides a method to prepare single-crystalline YIG films via room-temperature deposition and ex situ annealing for potential applications in high-frequency microwave devices.

The Influence of the Magnetic Field on the Plasma Characteristics in Hollow Electrodes Discharge System

This work is an experimental study about the effects of gas pressure and magnetic field on plasma characteristics produced in an internal hollow electrodes discharge (HED) system. The results show that the breakdown voltage values increase with increasing the working pressure (especially with the presence of a magnetic field). The breakdown voltage depends on the p.d. product, where p is the gas pressure and d is the distance between the electrodes. While the values of current discharge decrease with the increase of the working pressure. The temperature of electron and the number density of electron are calculated from the Boltzmann method and the broadening of Stark, respectively. The results showed that the electron number density ( ) and plasma frequency ( ) increase with increasing the gas pressure, especially with the presence of a magnetic field, i.e. the plasma is more stable with the presence of magnetic field. While the electron temperature ( ) and Debye length ( ) decrease with increasing the gas pressure.

Helium electron beam rf plasma for low-k surface functionalization

A complex simulation approach is applied to determine optimal conditions for the functionalization of low-k materials in e-beam rf discharge generated by 1 keV electron beam in He. The possibility and mechanisms of methyl group elimination from low-k surfaces with low-energy He ions and fast He atoms are studied with ab initio dynamic density functional theory-based simulations. The effect of gas pressure, rf voltage, and rf frequencies on the ion energy and angle distribution functions is analyzed using a 1D Particle-in-Cell Monte Carlo model. The relative contribution of fast atoms in the surface functionalization is estimated. Ion fluxes on the 2D trench walls and bottom are calculated with the developed analytical approach.

Numerical simulation and experimental verification of droplet transfer during local dry underwater MIG welding process of SUS304

Based on the fluid mechanics and electromagnetic theory, a numerical simulation model of droplet transfer during local dry underwater MIG welding (LDU-MIG) of SUS304 was established by using fluid dynamics software FLUENT. The effects of gas pressure, wire feeding speed (WFS) and pulse peak current on the whole droplet transfer process in LDU-MIG were simulated and investigated. The simulation results indicated that the increase of gas pressure reduced the plasma flow force and enlarged the pressure gradient in the local dry cavity, which hindered the droplet transfer process and led to the larger droplet diameters and longer transfer periods. The increase of WFS decreased transfer period in lower current, but it changed the droplet transfer modes in larger current. With the increase of pulse peak current, the droplet transfer modes changed from globular transfer (200 A) to projected transfer with one pulse one droplet (280 A), then to streaming transfer with one pulse multiple droplets (360 A). Finally, the droplet transfer process was captured by high-speed photography technology in LDU-MIG welding experiments, the simulation results were in good agreement with the experimental results, which provided theory guidance and data supports for manufacturing and remanufacturing of underwater structure.

Development and application of a miniature mass spectrometer with continuous sub-atmospheric pressure interface and integrated ionization source

For the miniature mass spectrometer (MS) with a continuous atmospheric pressure interface (CAPI), the gas in the multi-stage chambers directly affects the performance of the instrument. In this study, a sealed ionization chamber is designed to couple with a conventional mini CAPI-MS. In this configuration, the gas environment in the first ionization chamber can be flexibly changed to regulate the gas conditions throughout the entire instrument. By studying the effect of gas pressure on the performance of the instrument, we found that the instrument shows some unique advantages when the first ionization chamber is under sub-atmospheric pressure (SAP) conditions, such as reducing the load of the vacuum pump by 40%, achieving pump-free injection for gas and liquid samples, and improving the resolution by a factor of 2 without loss of detection sensitivity. Therefore, we propose a new integrated interface called continuous sub-atmospheric pressure interface (CSAPI) for building a miniature ion trap mass spectrometer. The CSAPI specially integrates sample introduction, gas/ions interface, and ionizations, including electrospray ionization (ESI) and secondary electrospray ionization (SESI), making this system more convenient for non-professional handlers to rapidly identify or monitor target analytes in gaseous- and solution-phase samples. We also use this system to study gas composition to further improve performance, being able to achieve a 5-fold sensitivity and 2-fold resolution improvement. At last, some custom applications of the current CSAPI-MS platform are explored and demonstrated, including real-time monitoring of chemical reactions in solution and long-distance sampling and analysis of dried Chinese herbs. In conclusion, this study provides a new approach to constructing a complete, versatile and practical miniature MS instrument.

Theoretical investigation of tritium concentration quantification method for DT fuel system using β-ray induced X-rays

Tritium measurement is one of the most important issues in DT fuel system of a fusion reactor. Beta-ray Induced X-ray Spectrometry (BIXS) method is a promising way to obtain tritium concentration in-line, especially for fuel processing system. However, till now there is no theory to establish the quantification relationship between tritium concentration and gas information including gas composition and pressure. Theoretical relationship between tritium concentration and X-ray spectrum in BIXS measurement is derived, and a quantitative method was proposed to determine tritium concentration directly by using the counts of X-ray spectrum. Non-linear Response Coefficients (NRCs) are introduced in the method to indicate the response of X-ray detector at different gas pressures for different gas compositions. Effects of both gas compositions (hydrogen/deuterium/tritium) and gas pressure (over five orders of magnitude, 1 Pa to 100 kPa) have been investigated quantitatively by Monte-Carlo simulations to determine the key parameters in the proposed method. Results show that for gas composed of hydrogen, deuterium, and tritium, NRCs are independent of gas composition within gas pressure from 1 Pa to 100 kPa. And NRCs can be obtained from the counts calculated within any energy region of X-ray spectrum detected in BIXS measurements. With the calculated NRCs, the tritium concentration can be obtained using only one reference experiment performed at any gas pressure (1 Pa to 100 kPa) for gas composed of any hydrogen isotopes. For gas composition including hydrogen, deuterium and tritium with different concentration, the error of NRCs in the proposed method is estimated to be 1.4%.

A study on moment tensor inversion of acoustic emission response on damaging localization of gas-bearing coal under load

During the deformation and fracture process, the acoustic emission (AE) signals can be produced for the of coal, rock and other solid materials, which revealing the damage localization evolution process. The effect of gas adsorption and pressure can change mechanical properties of coal mass and affect its damage development. Based on this, the experimental system for gas-bearing coal loading and AE monitoring was constructed, to analyze AE response characteristics under the joint action of loading stress and gas pressure on coal specimen. Afterwards, the damage localization evolution process of coal mass was studied with the moment tensor inversion method. Results showed that temporal response of AE signals was closely related to the damage degree and loading level of coal specimen, which could reveal its local severe damage and final failure characteristics. The spatial distribution and spread trend of AE fracture events inside coal specimen could be calculated through the moment tensor inversion method. It was basically consistent with the results of crack expansion on the specimen surface. The zones, where fracture events occurred intensively, gathered and spread in a continuous trend, were conductive to forming the macrocrack belt macroscopically. It could be regarded as the hazard zone with dynamic failure occurrence. Moreover, when the coal specimen faced the critical failure, the precursor characteristics of AE response appeared with the shear fracture events dominated markedly. The study results provide a new research idea for revealing the damaging localization evolution process under the coupling effect of stress and gas and lay the application foundation.

Hypervelocity penetration behavior and fireball radiation characteristics of tungsten-zirconium reactive projectile

Reactive damage elements has the dual properties of kinetic energy penetration and strong combustion/explosion and thus enhanced damage ability potentially. At present, research on the damage characteristics of reactive projectile is mostly limited to the velocity of projectile impacting target below 2km/s, and there are few reports on hypervelocity impact. The damage ability of high-density and high-strength tungsten-zirconium (W/Zr) alloy projectiles is enhanced in hypervelocity impact, because the degree of material being fragmented is high, the particle size is small, and the flying speed of particles is fast, which are all conducive to the combustion of reactive components to form continuous high-temperature fireballs. In order to investigate the hypervelocity penetration behavior of W/Zr reactive projectile and the radiation characteristics of fireball, the failure characteristics of W/Zr reactive projectile impacting titanium alloy plate with velocities of 1.842-4.039km/s were obtained by hypervelocity impact test. The effects of projectile impact velocity and ambient gas pressure on the combustion characteristics of impact fireball are analyzed. The evolution characteristics of equivalent radiation temperature and equivalent radiation area are obtained by fitting experimental data. The effects of environmental gas on radiation characteristics under different impact conditions are identified and analyzed.

Thermal lensing in copper vapor laser oscillator-amplifier configuration: Its measurement, role and compensation

A novel technique to measure the resultant focal length of the thermal lens in an amplifier using collimated beam of the oscillator for copper vapour laser system demonstrated. The resultant focal length was estimated using ray tracing approach in a 40 W system (CVL-40). Effect of input electrical power and neon buffer gas pressure on the resultant focal length was studied. Role of equivalent thermal lens in master oscillator power amplifier (MOPA) configuration was evaluated. Compensation techniques for minimization of the thermal lensing effect for a MOPA chain were theoretically studied using ray tracing in an equivalent lensing model. Compensation of thermal lensing for an eight module MOPA chain with CVL-40 (38 mm bore, 1.8 m long, 40 W, 9 kHz) systems studied. An eight-module MOPA chain configuration with minimized thermal lensing based on optimized compensation techniques is proposed. Our study finds benefits for high power laser systems used in various industrial, research and development applications like micromachining, high speed photography, bio-medical applications and pumping dye lasers for spectroscopy.

Transient surface charging of tri‐post insulator in SF 6 ‐filled direct current gas‐insulated transmission lines: Effects of electric conductivity, gas pressure, and voltage amplitude

Transient surface charging of tri‐post insulator in SF ₆ ‐filled direct current gas‐insulated transmission lines: Effects of electric conductivity, gas pressure, and voltage amplitude

Effect of gas pressure on the quality-factor of single-crystal diamond micro cantilevers

Single-crystal diamond (SCD) is a prominent semiconductor material due to its superior mechanical and physical properties. From the viewpoint of practical application, a low vacuum or atmospheric environment are preferred. Here we systematically investigated the effect of ambient gas pressure on the quality-factor (Q-factor) of SCD micro cantilevers, and analyzed the disparate energy dissipation mechanisms. The Q-factor around 7500 was found to be almost stable for ambient pressure <10 Pa, then decreased sharply by about three orders of magnitude with the pressure increasing up to 105 Pa gradually. The ambient pressure ranging from 10−3 to 105 Pa can be defined as intrinsic, molecular, and viscous regimes by Knudsen number. We found that the Q-factors of the SCD cantilevers can be well described by the analytical models corresponding to the three regimes.

Characteristic Diagnostics of a Laser-Stabilized High-Pressure Argon Plasma by Optical Emission Spectroscopy

Laser-stabilized plasma (LSP) attracts intense interests in lighting applications requiring extreme stability, long lifetime, and broad radiation range ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$10^{1}$ </tex-math></inline-formula> – <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$10^{4}$ </tex-math></inline-formula> nm). In this work, an argon LSP was generated at high pressures (>10 bar) by a focused laser beam, and its fundamental properties were studied in detail by the approach of optical emission spectroscopy (OES), with emphasis on the determination of plasma parameters including the electron temperature and density. The effects of argon gas pressure, laser power, and N2 mixture ratio, on the full-view of radiation spectra and electron parameters, were investigated experimentally. The results demonstrate that the increase of gas pressure or laser power density is a proper way to achieve higher optical radiation from the argon LSP, but not by adding molecular mixtures like N2.

Influence of Cylindrical Electrode Configuration on Plasma Parameters in a Sputtering System

In the present work, the effect of the cylindrical configurations of the sputtering device electrodes on the plasma parameters (Debye length, electron temperature, electron density, plasma frequency) is studied. Also, the effect of the argon gas pressure on the discharge properties is examined with gas pressures of (0.08, 0.2, 0.4 and 0.6) Torr. The properties of the plasma are diagnosed by optical emission spectrometry. The spectroscopic method is adopted for examining the atomic spectra of argon emission. The electron temperature is determined by the Boltzmann method. While, the Stark-widening method was employed for calculating the electron number density. The voltage against current curves of the cylindrical sprayer discharges shows the voltage to be nearly constant with slight increase in current. An increase in pressure causes the cathode cascades to compress and the negative glow to become thinner and more luminous. Plasma properties such as electron temperature and Debye length decrease with increasing pressure, while electron number density and plasma frequency increase.

Surface Charge Characteristics of DC-GIL Insulator Under Multiphysics Coupled Field: Effects of Ambient Temperature, Load Current, and Gas Pressure

In this article, the surface charge characteristics of the direct current gas-insulated transmission lines (DC-GIL) insulator under thermal–electric coupled fields are investigated. A horizontally installed GIL with a basin-type insulator is employed. The 3-D charge distribution under different ambient temperatures, load currents, and gas pressures is obtained based on the finite-element method. It is found that the charge density increases with increasing ambient temperature since the bulk conduction is promoted due to the increasing insulator temperature. At lower ambient temperature, the surface charge distribution shows a more obvious difference in different radial directions along the insulator due to the increasing difference in electric conductivity in different directions. With increasing load current, the charge density increases, and the difference in charge density in different radial directions becomes more obvious. The charge density increases with increasing gas pressure although the temperature decreases, which is attributed to the domination of decreasing ion mobility over decreasing bulk conduction. It can be concluded that attention should be paid to these conditions when dealing with the insulation property of DC-GIL considering the effect of thermal gradient on the charge accumulation. Besides, simulation based on a 3-D model is necessary, especially for horizontal GILs.

Hydrogen gaseous embrittlement effect over mechanical properties of an experimental X-120 microalloyed steel subjected to heat treatments and different cooling rates

This research work aimed to determine the hydrogen gas pressure effect on the mechanical properties of an experimental X-120 microalloyed steel, subjected to heat treatments and quenched in different mediums. The steel in its as-received condition was reheated at 900 °C and quenched in spray water (900QSW), pressurized air (900QPA), and emulsion of water-oil medium (900QWO) which produces complex microstructures formed by martensite–bainite–acicular ferrite; otherwise, reheated at 820 °C and quenched in oil media (820QO) which produces a banded martensite-polygonal ferrite microstructure. To determine the hydrogen embrittlement susceptibility, in-situ tension tests were developed at 1, 4, and 7 MPa of hydrogen gas pressure. The results showed that as hydrogen gas pressure increases, the mechanical properties reduce in all quenched conditions, being the most susceptible condition the 820QO sample which presented the higher embrittlement index; on the contrary, the less susceptible condition was the 900QPA sample.

Effect of pressure on biomethanation process and spatial stratification of microbial communities in trickle bed reactors under decreasing gas retention time

The current study investigated the effect of elevating gas pressure on biomethanation in trickle-bed reactors (TBRs). The increased pressure led to successful biomethanation (CH4 > 90 %) at a gas retention time (GRT) of 21 min, due to the improved transfer rates of H2 and CO2. On the contrary, the non-pressurized TBR performance was reduced at GRTs shorter than 40 min. Metagenomic analysis revealed that the microbial populations collected from the lower and middle parts of the reactor under the same GRT were more homogeneous compared with those developed in the upper layer. Comparison with previous experiments suggest that microbial stratification is mainly driven by the nutrient provision strategy. Methanobacterium species was the most dominant methanogen and it was mainly associated with the bottom and middle parts of TBRs. Overall, the increased pressure did not affect markedly the microbial composition, while the GRT was the most important parameter shaping the microbiomes.

Fundamental physics effects of background gas species and pressure on vapor plume structure and spatter entrainment in laser melting

First-principles modeling, based on the direct simulation Monte Carlo (DSMC) method, is applied to quantitatively explain the physics of stainless-steel (SS316L) vapor plumes and jets and powder particle entrainment under conditions relevant to laser welding and laser powder bed fusion additive manufacturing. The DSMC is a particle-based gas kinetic simulation approach, with few built-in assumptions, that resolves the Knudsen and diffusion layers in vapor microjets. The simulations are performed for different background gas species (argon, helium, and neon) at background gas pressures from 0.1 to 5 bar and molten pool temperatures from 3250 K to 4000 K. The simulations capture the evolution of the vapor jet structure from unsteady to steady-state vapor flow, the transition from subsonic flow at low surface temperatures to supersonic flow at surface temperatures close to boiling, as well as the effects of the background gas species and pressure. The simulations show that the vapor jet structure, as well as the magnitude and direction of the entrained gas close to the laser spot, greatly affects the process environment, creating particle spatter and denudation around the laser track. High pressure and lighter background gas can decrease the amount of spatter. At high pressure, the evaporation is reduced, which forms a low-velocity subsonic plume. For lighter gas species, the gas-entrainment velocity increases while the jet radius decreases which forces entrained particles to merge with the melt pool. The powder particle simulations reveal that the width of the denudation zone strongly depends on particle diameter and increases at low pressure and lighter background gas. This study emphasizes that the ambient gas species and the pressure in the build chamber should be treated as process parameters that are as important as controlling laser power and scan speed when trying to prevent defects. • Kinetic modeling reveals strong effect of molecular diffusion in AM vapor microjets. • The laser power and surface temperature stronlgy affect the transition from subsonic to supersonic vapor jet. • Ambient gas chamber species and pressure strongly affect the dynamics (gas, powder) near the laser spot. d. • Strong gas flow (helium) does not necessarily create more spatter as these merge with the melt pool and disappear. • The width of the vapor plume is more strongly dependent on the ambient gas pressure than on the laser beam size.