Large Gas Pressure Research Articles

Analysis of relative wavelength response characterization and its effects on scanned-WMS gas sensing* *Project supported by the National Natural Science Foundation of China (Grant Nos. 51906120 and 11972213), China Postdoctoral Science Foundation (Grant Nos. 2018M640125 and 2019T120088), and the National Basic Research Program of China (Grant No. 2016YFC0201104).

Our recently proposed three-step method showed the promising potential to improve the accuracy of relative wavelength response (RWR) characterization in the wavelength-modulation spectroscopy (WMS) over the commonly used summation method. A detailed comparison of the three-step method and the summation method, for the wavelength-scanned WMS gas-sensing, was performed with different laser parameters (modulation indexes and scan indexes) and gas properties (pressures and concentrations). Simulation results show that the accuracy of the predicted gas parameters is strongly limited by the RWR characterization with large modulation index and high gas pressure conditions. Both fitting residuals of RWR and errors of predicted gas parameters from the recently proposed three-step method are nearly 2 orders of magnitude smaller than those from the summation method. In addition, the three-step method is further improved by introducing a coupling term for the 2nd harmonic amplitude. Experiments with CO2 absorption transition at 6976.2026 cm−1 were conducted and validated the simulation analysis. The modified-three-step method presents an improved accuracy in RWR description with at least 5% smaller fitting residual for all conditions compared with the three-step method, although the deviation of the deduced CO2 concentrations between these two methods does not exceed 0.2%.

Effect of gas pressure on conduit plasma atomization for fabricating spherical stainless steel powder

In this study, spherical stainless steel powders are produced using the conduit plasma atomization. Parameters of the conduit plasma atomization process with gas variations of 1.5 bar pressure, 2 bar pressure, 2.5 bar pressure with 316L stainless steel raw material with a current of 25 Amperes, feed speed of 2 mm3/s. The results of stainless steel powders were observed using a digital microscope (Dino-Lite AM4115), scanning electron microscopy (SEM-FEI-Inspect F50), and energy dispersive spectroscopy (EDS). To ensure the purity of the resulting 316L stainless steel spherical powder, EDS was used for qualitative and quantitative elemental analysis. The results showed that the 316L stainless steel spherical powder particles varied in size from 35 µm to 140 µm, making them ideal for powders metallurgy application. The effect of gas pressure on the powder weight percentages for particle sizes 50 µm – 100 µm for 1.5 bar pressure, 2.0 bar pressure, and 2.5 bar pressure were 67.14%, 78.71%, and 81.73%, respectively. It is possible that this could happen because to break down molten metal into smaller size droplets, it is needed the kinetic energy of larger gas pressure. So that large gas pressure can produce more small particle size compared to small gas pressure.

Investigation on the Continuous Wave Mode and the ms Pulse Mode Fiber Laser Drilling Mechanisms of the Carbon Fiber Reinforced Composite.

The near infrared (NIR) laser drilling of a carbon fiber reinforced polymer (CFRP) composite in the continuous wave (CW) mode and the ms pulse mode was investigated by an experiment and a numerical simulation. The relationships between the laser penetrating time, entrance hole diameter, surface heat affected zone (HAZ) width, and material ablation rate and the laser irradiation time and laser peak power densities were obtained from the experiment. For the same average power density of the laser output, 3.5 kW/cm2, it was found that the ms pulse laser mode, which had a higher peak power density, had a higher drilling efficiency. When drilling the same holes, the pulse laser mode, which had the highest peak power density of 49.8 kW/cm2, had the lowest drilling time of 0.23 s and had the smallest surface HAZ width of 0.54 mm. In addition, it was found that the laser penetrating time decreased sharply when the peak power density was higher than 23.4 kW/cm2. After analyzing the internal gas pressure by the numerical simulation, it was considered that a large internal gas pressure appeared, which resulted from polymer pyrolysis, causing a large amount of the mechanical erosion of the composite material to improve the drilling efficiency. Therefore, the ms pulse laser showed its potential and advantage in laser drilling the CFRP composite.

Coupled hydrodynamic and kinetic model of liquid metal bubble reactor for hydrogen production by noncatalytic thermal decomposition of methane

Industrial-scale implementation of liquid metal bubble reactors (LMBRs) to produce hydrogen by methane decomposition will require large gas holdups (e.g., 20–30 vol%) and elevated gas pressures (>20 bar) to allow for practical reactor sizes. A realistic reactor design must account for the coupling between reaction kinetics and hydrodynamic effects. The gas holdup is predicted from the superficial gas velocity with a drift flux model that was experimentally corroborated in gas-molten metal mixtures. Large superficial gas velocities (>0.40 m s−1) are required to achieve gas holdups of about 25 vol% in liquid metal baths (LMBs). A noncatalytic kinetic model is developed to provide thermodynamically consistent decomposition rates at methane conversions approaching equilibrium. The coupled model optimizes the LMB dimensions (diameter and length) and the inlet pressure to minimize the volume of liquid metal when the hydrogen production rate, bath temperature, methane conversion, metal composition, and maximum gas holdup are specified. For example, 200 kt a−1 of hydrogen can be produced in an LMBR containing at least 96.5 m3 of molten tin held at 1100 °C in a bath measuring 3.50 m in diameter and 14.3 m in length, with an inlet methane pressure of 57.8 bar resulting in an average gas holdup of 29.7 vol% and a methane conversion of 65%.

Adequacy and security analysis of interdependent electric and gas networks

In this article, adequacy and security assessments on the coupled operations of the electric and gas networks are performed. Extreme operating conditions and fault of components are considered as events that can impact the interdependent systems. The electric and gas networks are represented by an event-based direct current power flow model and by a transient one-dimensional mass flow model, respectively. Furthermore, the automations and safety strategies enforced by transmission system operators are represented within an original modelling approach. A quantitative analysis is performed with reference to the simplified energy infrastructures of Great Britain. Results highlight the contingencies which can jeopardize security and identify the components that are prone to fail and induce large gas pressure instabilities and loss of supply, and the locations in the gas grid that are susceptible to pressure violation. Moreover, a simulated 30% increase of the peak gas demand in 2015 is a limit for safe operations of the gas network, but the coupled systems are robust enough to avoid the spread of a cascading failure across networks. These results allow preventing critical operating conditions induced by the interaction between networks and can guide safety-based decisions on system reinforcements and the development of mitigating actions.

Gas-particle flows and erosion characteristic of large capacity dry top gas pressure recovery turbine

Based on the erosion rate model and the particle rebound model of blade material obtained through accelerated erosion test under high temperature, systematic numerical simulations of the complex gas-particle flows in inlet volute and cascade of a large capacity gas pressure recovery turbine are performed in this paper. The influence of inlet volute structure and cascade channel structure on the aerodynamic performance and erosion characteristics of turbine is first investigated. Results show that although mixing flows and vortex flows are formed in turbine intake volute, total pressure loss of volute is less than 0.7% because of low gas velocity. Erosion damage on the trailing edge of nozzles and rotating blades is mainly caused by high-speed cutting behavior of ash particles. The typical inlet volute structure results in an uneven erosion of first stage nozzles along circumferential direction. Nozzles located below the horizontal split are mainly eroded in blade root area, while erosion distribution of nozzles located above the horizontal split is irregular, and worse than the erosion degree of the lower half circle. Flow acceleration characteristics and cascade circumferential structure must be comprehensively considered so as to simultaneously improve the aerodynamic and anti-erosion performance of turbine.

A pilot study on the vacuum degree online detection of vacuum interrupter using laser-induced breakdown spectroscopy

Vacuum degree online detection of vacuum interrupter has been a great challenge for decades. In this letter, a novel approach based on laser induced breakdown spectroscopy (LIBS) was proposed to solve this tough problem, which is suitable for non-intrusive, electro-magnetic interference free and remote detection. The spectral lines of Cu, H, N and O elements from the interrupter shield were detected for a large gas pressure range from p = 1 × 10−3 Pa to 1 × 105 Pa. It was found that the spectral intensities of O and H increase monotonically with gas pressure, in contrast the spectral intensity of Cu first decreases slightly and then increases. Their intensity ratios, especially for that of Cu to O, change dramatically and monotonically with the gas pressure when p ⩽ 0.1 Pa, indicating that they can be used for determining the vacuum degree values. Spectral ratio method fundamentally reduces the influences of the possible variation in measuring distance and the laser power fluctuation, making LIBS a promising method for vacuum degree online detection of vacuum interrupters.

Electro-Chemical Potential Analysis of Zirconium Based on the Reaction-Diffusion Equations of Oxygen Ion and Electron Considering Phase Transformation

Components of Solid Oxide Fuel Cells (SOFCs) are always exposed to high temperature and large gas pressure under operation, which leads gradually degradation in the performance of SOFC. One of the factors for degradation is attributed to the phase transformation in Ni-doped 8Yttria-Stabilized Zirconia (8YSZ) which is used for the electrolyte. 8YSZ originally takes a cubic structure with the Ni particles inside the lattice structure. Once fuel gas is injected to the anode, Ni particles of the 8YSZ electrolyte leave in the reduction atmosphere, which makes 8YSZ hexagonal structure. The electric properties changes according to such phase transformation. Therefore, it is important to simulate the distribution of oxygen potential considering the phase transformation in 8YSZ for the predication of the electric property of SOFC. In order to simulate oxygen potential in 8YSZ including the phase transformation, we employ the electro-chemo analyses developed in our previous report [1]. In the simulation, we use diffusion-reaction equations representing the evolutions of potentials of oxygen ion and electron. These evolution equations are coupled in the terms of the time based on the theory of local equilibrium law for the potential of oxygen. The equations have reaction terms to present the reaction currents generating due to the electrode reaction in electrodes. The non-stationary terms are modelled with the capacitance of oxygen and electron. The relation between electro-chemical potentials and currents of oxygen ion and electron are described by the Ohm’s law in this model. The material properties such as electric conductivities, capacitances and reaction currents of oxygen ion and electron depend on both the temperature and partial pressure of oxygen. These governing equations are solved after the discretization into finite elemental equations. In the previous report [1], the experimental data are used for the material properties in the calculation. However, the degradation due to phase transformation is not be considered. In this study, evolution equations for the electric conductivities of oxygen ion and electron are proposed. The equations represent the temporary deterioration in 8YSZ in terms of the electric conduction. The effects of the control period can be taken into account in the evolution equations. The phase transformation occurs depending on the equilibrium partial pressure of oxygen between Ni and NiO. The time constants, which are related to the duration of degradation of materials, are different in Ni and NiO, i.e., cubic structure or tetragonal structure material. The hole conductivity is also considered in the electric conductivity of electron. The time constants are associated with the temperature both in the materials before and after transformation. The tendencies of oxygen potentials calculated for 8YSZ are discussed with the experimental data. Based on the present model, the calculations are conducted for the 8YSZ electrolyte with Ni-YSZ for anode and LSCF for cathode in the both sides end. The boundary conditions of oxygen ion and electron are given as Neumann conditions with zero flux at both the end of anode and cathode, which is considered as the open circuit voltage (OCV) condition. The temperature is set as 1173K during the calculation, and partial pressure of oxygen is changed to 1.0×10-19 atm from 0.21 atm while partial pressure of hydrogen is changed to 0.97 atm to 1.0×10-19 atm during the initial 200s. Then, the 0.21 atm of partial pressure of oxygen and 1.0×10-19 atm of partial pressure of hydrogen are kept. As the result, the phase transformation due to the equilibrium pressure between Ni-NiO and degradation during long period control are reproduced. The phase transformation occurs in the area between the center of electrolyte and anode. After the completion of phase transformation, the gap of the oxygen potential migrates to anode due to the degradation of 8YSZ. [1] K. Terada, T. Kawada, K. Sato, F. Iguchi, K. Yashiro, K. Amezawa, M. Kubo, H. Yugami, T. Hashida, J. Mizusaki, H. Watanabe, T. Sasagawa and H. Aoyagi, “Multiscale Simulation of Electro-Chemo-Mechanical Coupling Behavior of PEN Structure under SOFC Operation”, ECS Trans., 35, 923-933 (2011).

Vertically aligned dust particles under the influence of crossed electric and magnetic fields in the sheath of a radio frequency discharge

We present experiments on two dust particles with a size of a few microns that are levitated in the sheath region of an rf discharge in the presence of an external magnetic field transverse to the sheath electric field. The two particles are vertically aligned due to the ion focusing effect. First, it is observed that the magnetic field causes a displacement of the dust particles either in the E→×B→- or in the opposite direction. Second, at a sufficiently large neutral gas pressure, the vertical alignment breaks up when the magnetic field strength is increased. The occurrence of this dissociation is described by the horizontal force balance on the two particles.

Electron heating during discharges driven by thermionic emission

The heating of plasma electrons during discharges driven by thermionic emission is studied using one-dimensional particle-in-cell Monte Carlo collisions modeling that self-consistently takes the dependence of the thermionic current on the plasma parameters into account. It is found that at a gas pressure of 102 Pa the electron two-stream instability is excited. As a consequence, the electrostatic plasma wave propagates from the cathode to the anode. The trapping of electrons by this wave contributes noticeably to the heating of the plasma. At a larger gas pressure, this instability is not excited. As a consequence, plasma electrons are heated only because of the generation of energetic electrons in ionization events and the scattering of emitted electrons.

Reassessing molecular sieving by kinked carbon nanotubes

Based on molecular dynamics simulations for the transport of pure nitrogen (N2), oxygen (O2) and their mixture in kinked single-walled carbon nanotubes (SWCNTs), molecular sieving by the kinked model of SWCNTs is presented. The influences of gas pressure, temperature and the component ratio of N2 in the mixture on gas separation are investigated. Considering the tradeoff between the permeability and the purity of O2, the results show that a large gas pressure, 300–500 K of gas temperature and a low component ratio of N2 in the N2–O2 mixture can be advantageous to the efficiency of gas separation. The purity of O2 can be kept higher than 80% when the component ratio of N2 is lower than 3/4, which will be advantageous to the design of multi-level gas separation mechanisms. The findings may provide theoretical references for the design and manufacture of molecular sieving devices in engineering applications.

Pressure Generation in a Coke Oven Chamber at Coal Charging

Displacement of coke oven chamber wall and gas pressure in the chamber was measured during carbonization, especially focused on the coal charging, in order to realize the load to the actual chamber wall. Maximum wall displacement and very large gas pressure peak were observed at CMC coal charge with 6-7% moisture. They started with coal charging and reached maximum at the end of the charging. The gas pressure at charging was higher at oven bottom and smaller for upper part. The gas pressure peak at charging was larger than the pressure in the later carbonization period or internal gas pressure. Wall displacement and gas pressure peak at coal charging were both small in a case of wet coal charge with over 9% moisture. High gas pressure generation in CMC coal charge was thought due to the carbonization gas and the low gas permeability of coal bed. The permeability of CMC coal bed is lower than that of wet coal due to not only the higher bulk density but also moisture itself. The difference in permeability together with the gas generation was large enough to explain the observed difference in the peak gas pressure.

Influence of phase memory effects in collisions on a resonance Raman spectrum

The influence of phase memory effects on the spectrum of resonance Raman scattering by three-level atoms with the Λ configuration of levels experiencing collisions with buffer gas atoms in a strong monochromatic radiation field is studied theoretically. Systems with a small Doppler broadening compared to the collision frequency (large buffer gas pressures) are analysed in the general case of an arbitrary change (from complete change to complete preservation) in the phase memory at any of three transitions in the Λ system. It is shown that in the absence of the collision relaxation of the low-frequency coherence at the transitions between two lower levels of the Λ system, the radiation scattering spectrum has a spectrally narrow component at the Raman frequency, which, despite the homogeneous broadening of the absorption line, exhibits a strongly pronounced anisotropy. In the direction, close to the propagation direction of exciting radiation, this line maximally narrows down. It is significant that upon optical pumping to the level unaffected by a strong field the resonance Raman spectrum noticeably differs from the spectrum in the case of the probe field. A simple expression is proposed for calculating the degree of the phase memory preservation in collisions from the relative amplitude of the Raman resonance.

High‐Intensity Discharge Lamp with Mo–SiO2 Functionally Graded Material

We show the invention of the new type of hermetically sealed high‐intensity discharge lamps, made of Mo–SiO2 functionally graded material (FGM) as an electrode and a sealing component. In the case of high‐intensity discharge lamps with Mo–SiO2 FGM (FGM lamp), the thermal expansion coefficient between Mo and SiO2 is functionally graded so that it tolerates a large number of heating cycles, with no cooling system required. Furthermore, lamps survive without breakage. The W electrode is totally separated from the lamp envelope by the FGM, so that no leakage of the luminous elements or gases takes place, when a large gas pressure exists inside a lamp.

Rathole stability analysis for aerated powder materials

Forty years ago, Jenike [Gravity Flow of Bulk Solids, Bulletin 108, Utah Engineering Station, 1961] and Johanson [Flow Indices in the Prediction of Powder Behavior, Pharmaceutical Manufacturing International, pp. 159–164, 1995] developed the flow-no-flow equations used to predict stability of bulk solid structures in silos and hoppers. These equations were developed into a theory that has been used to design process equipment to handle cohesive materials. The basis of the theory is a limiting stress state analysis of a bulk material forming a cylindrical pipe (rathole) around or an arch across the hopper outlet. Reliable process operation requires that these two cohesive obstructions be avoided to achieve proper flow of bulk materials through process equipment. Today, industry uses a variety of flow aid devices to overcome these stable flow structures. One such device is aeration pads which are used to maintain fluidization of fine powders and decrease cohesive behavior of bulk materials. Alternatively, air blasters can inject a given quantity of gas into the bulk material creating large transient gas pressure gradients that may destroy these cohesive structures in process equipment. It is important to note that air blasters may destroy cohesive structures provided they are placed in close enough proximity to the stable rathole and with sufficient frequency along the axis of the bin or around the bin perimeter. Although these aeration techniques work, a full understanding of the reason is lacking. Currently, both the placement and required number of these flow aid devices are based on practical experience and not sound theoretical principles. This paper addresses this knowledge void by adding the gas pressure gradient terms to the rathole stability analysis performed by Jenike, thus extending the flow-no-flow rathole analysis to aerated conditions.

High-field measurement of the129Xe−Rbspin-exchange rate due to binary collisions

We have measured the binary spin-exchange rate coefficient for collisions between Rb and ${}^{129}\mathrm{Xe}$ atoms at a magnetic field $B=9.4\mathrm{T}$ and in the temperature range $160<T<200\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}.$ The longitudinal spin-relaxation rate ${1/T}_{1}$ of ${}^{129}\mathrm{Xe}$ is dominated by ${}^{129}\mathrm{Xe}\ensuremath{-}\mathrm{Rb}$ binary collisions. We measured ${1/T}_{1}$ using the methods of conventional nuclear magnetic resonance, with no spin enhancement by optical pumping. At the high magnetic field and large gas pressures used in this work, the contribution of ${}^{129}\mathrm{Xe}\ensuremath{-}\mathrm{Rb}$ molecules to the spin-exchange rate was less than 0.1% of the binary-collision rate. The Rb atomic number density [Rb] was measured directly from the large Faraday rotation of the polarization of near-resonant light passing through the sample cells. The rate coefficient is $\ensuremath{\kappa}{=d(1/T}_{1})/d[\mathrm{Rb}]=(1.75\ifmmode\pm\else\textpm\fi{}0.12)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}16}{\mathrm{cm}}^{3}/\mathrm{s}.$

Numerical modeling of the behaviour of high pressure vessel under hypervelocity impact

The increase of the number of space debris, particularly in LEO, has become a menace for space missions, and Space Agencies such as CNES (French Space Agency) are worried about this phenomenon. Because high pressure vessels are critical components onboard satellites, it is important to know their behaviour under hypervelocity impact induced by space debris. The aim of the study supported by CNES is to establish the different possible regimes (penetration, rupture, explosion, fragmentation) of the tank as a function of the critical parameters. The pressure vessel considered for this study is an over-wrapped carbon fibre on a titanium liner. The gas (xenon or helium) is stored under high pressure (15 or 31 MPa). The menace is characterised by an aluminium sphere, from 0.1 to 5 mm in diameter, and with a 5 up to 20 km·s −1 velocity. Our theoretical approach is a 2D and 3D simulation using the SPH (Smooth Particle Hydrodynamic) technique coupling the gas and the tank. The mechanical part of the code has been calibrated on experimental results available in the literature. Our model allows exploring a wide range of parameters which are not accessible to ground experimental simulations. We have identified three main potential causes for a possible tank explosion: (1) the growth of a shock wave in the gas; (2) the effect of the compressive waves in the gas on the composite and of the direct high amplitude mechanical waves within the composite; (3) the degradation of the back wall by the flying debris which can then rupture under the residual solicitation by the gas. A larger gas pressure, a smaller tank and replacing helium by xenon makes the scenarios (1) and (2) more dangerous. The scenario (3) appears to be also important to consider. Our results will be extended and validated by direct comparison with experimental tests on pressure vessels.

8.6. Magnetic reconnection as the origin of superhot plasmas in the Galactic center

Recent X-ray astronomy satellite (e.g., Ginga, ASCA) has revealed that the center of our Galaxy is filled with a large amount of very hot plasmas (a few − 10 keV) on a scale of 100 pc, which are referred to as superhot plasmas. These plasmas are similar to the Galactic Ridge X-ray Emission (GRXE; cf Tanuma et al. 1997), but with larger gas pressure, and their formation mechanism has been a big puzzle. Here we propose a new model, magnetic reconnection model (Fig. 1), to explain the heating as well as the confinement of the Galactic center superhot plasmas, by performing MHD numerical simulations of magnetic reconnection in the situation suitable for the Galactic center. In our model, the magnetic field is amplified by the rotation of the Galactic gas disk (Fig. 2), and inflate from the disk to outside by the Parker instability. The inflating magnetic loop collides with ambient field lines, thus inducing the magnetic reconnection (the same process applied to the solar corona is shown in Yokoyama and Shibata 1995). In this model, energy release per single reconnection event is ΔE ≈ emVrec ≈ 2 × 1051 erg where em = P/β is the energy density of toroidal magnetic field, Vrec = λ2δ is the volume of the event, λ ≈ 60pc is the most unstable wavelength of the Parker instability, and δ ≈ 3pc is the thickness of the Galactic disk. The occurrence rate of this event is f ≈ N/Δτdep ≈ (3 × 104 yr)−1 where N = Vdisk/Vrec is the number of current sheets in the disk, Vdisk is the volume of the disk, and Δτdep is the time scale of energy deposit which is comparable with the time scale of the Galactic rotation. Then, the heating rate is h = fΔE = 2 × 1039 erg s−1 = 100L2–10keV.

Non-linear effects on neutral gas transport in divertors

The effects of neutral particles on the condition of the plasma edge play a key role in divertor and limiter physics. In computational models they are usually treated in the linear test particle approximation. However, in some divertor concepts a large neutral gas pressure is required in the divertor chamber to provide sufficient neutral-plasma interaction in the plasma fan (momentum removal and energy dissipation) and to permit adequate pumping performance. In such regimes viscous effects in the neutral gas may become relevant. We have extended the EIRENE code to solve the Boltzmann equation with a non-linear BGK-model collision term added to its standard linear collision integrals. The linear in-elastic collision integrals are reconsidered with respect to volume recombination and momentum removal efficiency from the plasma. The numerical procedure in the EIRENE Monte Carlo code is outlined. A simple test application (Couette flow) shows that the procedure works properly. First numerical studies have been carried out and the results are discussed.

Multi-conical instability in the passive ring cavity: linear analysis

The instability threshold characteristics are derived for the ring cavity with passive weakly absorbing two-level atoms cell. Emission of several conical shells is predicted, depending on the optical arrangement, and on the buffer gas pressure. In the case of pure vapor, each conical shell has its own frequency, while all the conical shells display the same frequency in case of large buffer gas pressure.