Initial Gas Pressure Research Articles

Generation of photoionized plasmas in the laboratory: Analogues to astrophysical sources

AbstractImplementation of a novel experimental approach using a bright source of narrowband x-ray emission has enabled the production of a photoionized argon plasma of relevance to astrophysical modelling codes such as Cloudy. We present results showing that the photoionization parameter ζ = 4πF/ne generated using the VULCAN laser was ≈ 50 erg cm s−1, higher than those obtained previously with more powerful facilities. Comparison of our argon emission-line spectra in the 4.15 - 4.25 Å range at varying initial gas pressures with predictions from the Cloudy code and a simple time-dependent code are also presented. Finally we briefly discuss how this proof-of-principle experiment may be scaled to larger facilities such as ORION to produce the closest laboratory analogue to a photoionized plasma.

Thermodynamic Characteristics of Methane Adsorption of Coal with Different Initial Gas Pressures at Different Temperatures

The adsorption of methane in coal depends on both pressure and temperature, and the adsorption gas content decreases as the temperature rises while increases as the pressure increases. When the gas molecule switches between the free state and adsorbed state, energy exchange is accompanied. To study the thermodynamic characteristics (adsorption heat, adsorption content, and adsorption time) of the methane adsorption of coal, the isothermal methane adsorption experiments of coal with different initial free gas pressures at different temperatures (30–90°C) were conducted. In this paper, a well-defined mathematical function of the adsorption heat was established on the basis of the actual gas state equation, Boltzmann energy distribution theory, and the two-state energy model, and the function was verified by the experimental data. The results show that the mathematical function of the adsorption heat can well describe the relationship among the adsorption heat, temperature, and initial free gas pressure in the closed adsorption system, and the adsorption heat involves the initial free gas pressure. The greater the initial free gas pressure, the less the adsorption heat is. In the adsorption process with different initial free gas pressures at different temperatures, the real-time free gas content increases with time and the adsorption system shows desorption process generally. For the adsorption process with the same initial free gas pressure, the adsorption time increases with the rising temperature. For the adsorption process with different initial free gas pressures at the same temperature, the greater the initial free gas pressure, the shorter the adsorption time it takes to reach an equilibrium state. The results help to understand the thermodynamic characteristics and the heat and mass transfer of methane in coal adsorption.

Calculation and Analysis of Electrophysical Processes in a High-Power Plasma Accelerator with an Intrinsic Magnetic Field

We have considered basic theoretical models describing various aspects of the formation and acceleration of plasma in pulsed accelerators. The discharge current, magnetic field, and plasma bunch velocity have been determined experimentally at different initial gas pressures in the accelerator chamber. We have considered the correspondence of some theoretical models of plasma acceleration to experimental data obtained in a KPU-30 coaxial accelerator. It is shown that the formation of the plasma in the coaxial accelerator depends on the plasma density, and acceleration processes at densities higher and lower than a certain transient density value on the order of 1011–1012 cm–3 are different. At a density higher than this critical value, the plasma is accelerated by a magnetic force. At the same time, at a low plasma density, plasma can be accelerated by an internal electric field.

Crack Initiation Characteristics of Gas-Containing Coal under Gas Pressures

In deep coal mines, coal before the working face is subjected to coupled high mining-induced stress and gas pressure. Such condition may facilitate crack formation and propagation in the coal seam, leading to serious coal and gas disasters. In this study, the mechanical properties (i.e., uniaxial compressive strength, tensile strength, and fracture toughness) of gas-containing coal with four levels of initial gas pressure (i.e., 0.0, 0.5, 1.0, and 1.5 MPa) were investigated by uniaxial compression, Brazilian disc, and notched semicircular bending loading test. A newly developed gas-sealing device and an RMT-150 rock mechanics testing machine were used. Fracture modes under different initial gas pressures were also determined. A theoretical method of fracture mechanics was used to analyze crack initiation characteristics under gas adsorption state. Results show that the uniaxial compressive strength, tensile strength, and fracture toughness of gas-containing coal decreased with increasing initial gas pressure. The tensional fracture occurred in gas-containing coal under uniaxial compressive loading with high gas pressure. Cracks in gas-containing coal propagated under small external loads due to the increase in effective stress of crack tip and decrease in cracking strength. This study provided evidence for modifications of the support design of working face in deep coal mines. Furthermore, the correlations between fracture toughness, compressive strength, and tensile strength of gas-containing coal were investigated.

Influence of Density Separation of Selected South African Coal Fines on the Products Obtained during Liquefaction Using Tetralin as a Solvent

The liquefaction of two South African discarded coal fines and their density separated (float) fractions were carried out under moderate conditions in a laboratory autoclave. Liquefaction tests were carried out on both discarded coal fines and their float fraction samples at temperatures ranging between 380 and 420 °C using tetralin as a solvent and an initial nitrogen gas pressure of 3 MPa. Oil samples produced from the liquefaction of coal fines discards and their float fractions were further characterized using gas chromatography–mass spectrometry (GC–MS) and nuclear magnetic resonance. The liquefaction test results showed that carbon conversions and oil yields were higher for the float fractions when compared to the discarded coal fines samples. The oil yields ranged from 24.4–37.2% (dry ash free (daf)) for the oil produced from the float fractions of the coal fines and 19.1–29.3% for oils produced from the coal fines (daf). The oil and the gas yields of the float fraction samples were higher when com...

Расчет и анализ электрофизических процессов в мощном импульсном ускорителе плазмы с собственным магнитным полем

AbstractWe have considered basic theoretical models describing various aspects of the formation and acceleration of plasma in pulsed accelerators. The discharge current, magnetic field, and plasma bunch velocity have been determined experimentally at different initial gas pressures in the accelerator chamber. We have considered the correspondence of some theoretical models of plasma acceleration to experimental data obtained in a KPU-30 coaxial accelerator. It is shown that the formation of the plasma in the coaxial accelerator depends on the plasma density, and acceleration processes at densities higher and lower than a certain transient density value on the order of 10^11–10^12 cm^–3 are different. At a density higher than this critical value, the plasma is accelerated by a magnetic force. At the same time, at a low plasma density, plasma can be accelerated by an internal electric field.

Research on Theoretical Model of Dynamic Bulk Modulus of Gas-Containing Hydraulic Oil

The bulk modulus of the gas-containing hydraulic oil is an important indicator reflecting its compressibility, directly affecting the stability, accuracy, rapidity, and reliability of the fluid transmission system. In the time-varying system with high speed and pressure, since the gas release rate differs from the gas dissolution rate, there exists a large difference between the static and dynamic values of the bulk modulus of hydraulic oil. Therefore, it is necessary to research the dynamic bulk modulus of the gas-containing hydraulic oil. Based on the improvement of Henry's law and gas-polytropic-process equation, a modified model of dynamic bulk modulus of the gas-containing hydraulic oil was proposed. Through the analysis of parameter influence, the influence of initial gas content and pressure on the dynamic bulk modulus of the gas-containing hydraulic oil during compression and expansion was discussed. Comparing the modified model and the Zhou model with the experimental results, the goodness of fit between the Zhou model and the experimental results during compression and expansion was 0.9936 and 0.9864, respectively. And the goodness of fit between the modified model and the experimental results during compression and expansion was 0.9937 and 0.9936, respectively. The prediction precision of the dynamic bulk modulus was improved while verifying the accuracy of the modified model. This research can provide a reference for optimizing the theoretical model of the dynamic bulk modulus of the gas-containing hydraulic oil.

Experimental investigations on tetrahydrofuran – methane – water system: Rapid methane gas storage in hydrates

This study reports methane (CH4) gas storage capacity along with TetraHydroFuran (THF) as guest molecules in mixed hydrates. This process has been studied in two reactors of 100 and 400 mL capacity, having 4.5 and 7.5 cm internal diameter respectively, in non-stirred configuration. Experiments were conducted in each reactor at constant initial gas pressure (7.5 MPa) and by increasing the height of the solution from 1 to 8 cm, resulting in volume scale-up factor of 5. The total CH4gas uptake (moles) passes through a maximum at around 50% volume of the reactor indicating a transition from gas-rich to solution rich conditions. Observed variations in gas uptake are within ±20% of the maximum, upon different solution volume from 35% to 70% of reactor’s volume. Another set of experiments were conducted keeping the amount of the solution constant and increasing gas pressure in the range of 0.5–11.0 MPa. The gas uptake increased upon an increase in the gas pressure, but this is at least 40% less compared to the theoretical estimate. The stirring of solution or addition of promoter (Sodium Dodecyl Sulfate, SDS) is also not effective in increasing the gas consumption. Kinetics of gas uptake, in both stirred and non-stirred conditions, are quicker and 90% of gas consumption occurs in an hour after the hydrate nucleation event.

A Gas Seepage Modeling Study for Mitigating Gas Accumulation Risk in Upper Protective Coal Seam Mining Process

Protective coal seam mining (PCSM) is one of the most significant mitigation measures of regional outburst in the process of deep coal seam mining, which has high outburst risk in China. During the PCSM process, the phenomenon of methane concentration exceeding the limit usually occurs in the working face. It is vital to understand factors affecting gas emission from the protective seam working face (PSWF) and to obtain an equation for determining the quantity of gas emission. A gas seepage model (GSM) was developed to simulate the gas emission during the process of upper PCSM. In this study, an equation was formulated to determine the quantity of gas desorbed from the protected seam into PSWF. These equations have been developed by using Fick’s second law of diffusion and Darcy’s flow law. The relationship between permeability and stress was described in an elastic-plastic state, and the mechanics of surrounding rock were investigated. It can be concluded from GSM that the initial gas pressure of protected seam, the characteristics of interlayer rocks, and the ventilation pressure of PSWF were the main factors that influenced the desorption of gas emission from the protected seam into PSWF. The developed GSM was tested for calculating gas emission quantity from the PCSM process by utilizing the actual geological condition data of a coal mine, which is located in Hancheng, China. The results have shown great agreement with obtained field measurements, which is done by combining the fitting curve of ventilation air methane quantity for PSWF with an interlayer spacing. A loss coefficient (δ) of 1.012 × 10−3 was obtained in this study.

Thermodynamic Stability Analysis of Microbubbles Confined in a Liquid Droplet.

A thermodynamic stability analysis of microbubbles in an enclosed volume of a volatile liquid-noncondensable gas solution was performed. The stability conditions for the formation of the bubbles and the relationship between the equilibrium bubble radius and the equilibrium bubble number were investigated. The calculation results show that even if the saturation vapor pressure of a volatile liquid is higher than the pressure of the liquid phase, stable noncondensable gas bubbles appear in a closed system. Under such a condition, if the initial pressure of the noncondensable gas, which is proportional to the total number of moles of a noncondensable gas in the system, increases, stable bubbles appear at a lower temperature. At a fixed parameter of h0, which is defined as the ratio of the saturation vapor pressure of the volatile liquid minus the pressure in the liquid phase to the initial pressure of the noncondensable gas, the equilibrium bubble radius increases with a decrease of the equilibrium bubble number.

Preparation of Cast Mo2B5 by Self-Propagating High-Temperature Synthesis Metallurgy Methods

This paper reports the preparation of cast dimolybdenum pentaboride by a self-propagating high-temperature synthesis (SHS) metallurgy method. Experiments were carried out in SHS reactors at an initial excess gas (Ar) pressure p0 = 5 MPa. In the experiments, we used thermite-type starting mixtures consisting of molybdenum oxide, aluminum, boron oxide, and elemental boron powders. The combustion of such mixtures yields two types of final product: Mo2B5 and Al2O3. The combustion temperatures of the starting mixtures used in our experiments have been shown to exceed the melting points of the final products, which are thus formed in a liquid (cast) state. Under the effect of gravity, the heavier phase Mo2B5 settles down to form a lower ingot, whereas the lighter phase Al2O3 forms an upper ingot. The synthesis products have been characterized by X-ray diffraction and local microstructural analysis. The results demonstrate that the composition and amount of the starting mixture have a significant effect on the synthesis parameters and the composition and microstructure of the Mo2B5. We have optimized conditions for the preparation of single-phase cast dimolybdenum pentaboride.

Controllable non-ideal plasmas from photoionized compressed gases

Based on a suite of molecular dynamics simulations, we propose a strategy for producing non-ideal plasmas with controllable properties over a wide range of densities between those of ultracold neutral plasmas and those of solid-density plasmas. We simulated the formation of non-equilibrium plasmas from photoionized, cool gases that are spatially precorrelated through neutral–neutral interactions that are important at moderate-to-high pressures. A wide range of physical properties, including Coulomb collisional rates, partial pressures, screening strengths, continuum lowering, interspecies Coulomb coupling, electron degeneracy and ionization states, were characterized across more than an order of magnitude variation in the initial gas pressure. A wide range of plasma properties are also found to vary when the initial pressure of a precorrelated gas is varied. Thus, we propose that non-ideal plasmas with tunable properties can be generated by photo-ionizing a dense, precorrelated gas. We find that the optimal initial density range for the gas is near a Kirkwood/Widom–Fisher line in the neutral-gas phase diagram. This strategy for generating non-ideal plasmas suggests experiments that have significant advantages over both ultracold and solid-density plasma experiments because the collisional, collective and recombination timescales can be tuned across many orders of magnitude, potentially allowing for a wider range of diagnostics. Moreover, the added costs of cooling ultracold plasmas and diagnosing dense matter with x-rays are eliminated.

SHS Metallurgy of Cr2AlC MAX Phase-Based Cast Materials

A review of publications on the structure, properties, fabrication methods, and application fields of materials based on the Cr2AlC MAX phase is given. It is noted that the most promising method of formation of such materials is self-propagating high-temperature synthesis (SHS), one of the directions of which is SHS metallurgy. A powder mixture of chromium III and chromium VI oxides of the analytical grade, aluminum of ASD-1 grade, and carbon is used as the base charge in investigations. The adiabatic combustion temperature and composition of final products is calculated using the THERMO special program. Experiments were performed in an SHS reactor with volume V = 3 dm3 under the initial pressure of inert gas (Ar) P0 = 5 MPa. The influence of the ratio of initial reagents on SHS parameters (the combustion rate, pressure increment, and yield of the target product), composition, and microstructure of target products is investigated experimentally. A scientific approach of the formation of cast materials in the Cr–Al–C system consisting of the Cr2AlC MAX phase and phases Cr3C2 and Cr5Al8 by the SHS metallurgy method is developed. The structural-phase states of target products are studied. It is established experimentally that, varying the content of initial reagents (aluminum and carbon) in the charge, it is possible to substantially affect the synthesis regularities, composition, and microstructure of final products. An increase in the content of the Cr2AlC MAX phase in the final product and a decrease in the Cr5Al8 content occur with an increase in the carbon content (above stoichiometric) in the initial mixture. An increase in the aluminum content (above stoichiometric) in the initial mixture leads to an increase in the content of the Cr2AlC MAX phase in the final product and a decrease in the content of the Cr3C2 phase.

Turbulent Spray Combustion Modeling Using Various Kinetic Solvers and Turbulence Models

Turbulent spray combustion of n-dodecane was modeled at relevant engine conditions using two combustion models (direct integration of chemistry (DIC) and flamelet generated manifolds (FGM)) and multifidelity turbulence models (dynamic structure large eddy simulation (LES) and renormalization group (RNG) Reynolds-averaged Naiver–Stokes (RANS)). The main objective of this work is to study the effect of various combustion and turbulence models on spray behavior and quantify these effects. To reach these objectives, a recently developed kinetic mechanism and well-established spray models were utilized for the three-dimensional turbulent spray simulation at various combustion chamber initial gas temperature and pressure conditions. Fine mesh with a size of 31 μm was utilized to resolve small eddies in the periphery of the spray. In addition, a new methodology for mesh generation was proposed and investigated to simulate the measured data fluctuation in the CFD domain. The pressure-based ignition delay, flame lift-off length (LOL), species concentrations, spray, and jet penetrations were modeled and compared with measured data. Differences were observed between various combustion and turbulence models in predicting the spray characteristics. However, these differences are within the uncertainties, error, and variations of the measured data.

Gas flow field evolution around hydraulic slotted borehole in anisotropic coal

Currently, hydraulic slotted borehole technology for strengthening gas drainage is one of the main measures to control gas disasters in deep mines. In this paper, to analyze the evolution of gas flow field around the hydraulic slotted borehole, the borehole gas drainage was simulated based on the anisotropy of coal structure and the established multi-field (namely, coal deformation field, diffusion field and seepage field) coupling model. Then, the influences of characteristic parameters, including, initial diffusion coefficient, diffusion attenuation coefficient, initial gas pressure and initial permeability, on the gas production rate and reservoir parameters of hydraulic slotted borehole gas drainage were analyzed. Finally, the results were verified by comparing the model simulation with field tests in Yangliu Mine. The results show that the anisotropy of coal affects the effect of borehole gas drainage. The initial diffusion coefficient D0 and the diffusion attenuation coefficient λ have opposite effects on key parameters of coal. With a larger D0, it is easier for gas in matrix pores to diffuse into the fracture system, and accordingly the gas production rate and relative permeability grow. A larger λ makes it harder for gas in matrix pores to diffuse into fractures, thus decreasing the gas production rate and relative permeability. The initial gas pressure pm0 and the initial permeability kfx0 and kfy0 exert the same effect on the key parameters of coal. The larger their values are, the more easily the gas in fractures can be extracted under the same negative pressure of drainage, which contributes to the diffusion of gas from the matrix into the fracture system under the action of pressure difference. Through combining actual monitoring results of 3# and 4# drilling fields in Yangliu Mine and the results of numerical simulation, it is acquired that the gas production rate measured in situ coincides with the rate simulated by the model, verifying the feasibility and engineering applicability of the model.

Experimental study on coal and gas outburst and the variation characteristics of gas pressure

With a self-designed physical simulation test system for coal and gas outburst and instantaneous gas desorption of coal, orthogonal tests were designed and conducted to investigate the influences of initial gas pressure, coal particle size and outburst mouth diameter on coal and gas outburst firstly, then gas pressure variation tests were conducted under different initial gas pressures and coal quantities to investigate the variation characteristics of gas pressure. The results show that the influence of outburst mouth diameter on the intensity and duration time of coal and gas outburst was biggest followed by coal particle size and initial gas pressure. The total outburst time was shorter when outburst mouth diameter was bigger, meanwhile the outburst intensity and outburst distance were larger when initial gas pressure was higher, coal particle size was smaller or outburst mouth diameter was larger. In some gas pressure variation tests, the maximum instantaneous gas pressure exceeded the initial gas pressure when the latter was larger, which means the initial gas pressure play a crucial role in coal and gas outburst initiation. Finally, the critical initial gas pressure and gas content were calculated as a reference to predict coal and gas outburst danger.

Multiphase flash calculation for system containing TBAB semiclathrate: Application to semiclathrate-based post-combustion CO2 capture

A algorithm coupled with modified Patel-Teja equation of state and Chen-Guo hydrate model is developed to conduct vapor-liquid-semiclathrate multiphase flash calculation for TBAB containing systems. To quantitatively describe the gas consumption ability of semiclathrate slurry, a new concept, i.e., the apparent liquid phase, is introduced. The Patel-Teja equation of state (PT EOS) combined with a Debye-Hückel electrostatic term is chosen to describe the fugacity of TBAB in aqueous solution and calculated gas solubility in aqueous phase. The Chen-Guo hydrate model is extended to calculate the fugacity of TBAB in semiclathrate phase. Several parameters in Chen-Guo model for TBAB are retuned by correlating phase equilibrium data. A mathematical approach based on the secant iteration is successfully applied to solve flash calculation. Results from flash calculations are in satisfactory agreement with experimental data reported in other literature. This new algorithm provides an extended range of calculations for semiclathrate phases, such as amounts of semiclathrate formed, and then, the contributions of absorption and hydration upon separation performance can be quantitatively described. In addition, multistage separation are simulated using this flash algorithm. The effects of TBAB concentration of solution, initial gas liquid volume ratio, temperature, and pressure on separation efficiency are systematically discussed from the perspective of thermodynamics and mass balance.

Cooperative effect of surfactant addition and gas-inducing agitation on methane hydrate formation rate

This paper reports experimental measurements of the isothermal and isochoric formation kinetics of methane hydrate in sodium dodecyl sulphate (SDS) solutions of various concentrations with gas-inducing agitation, and the results are compared with those obtained with normal agitation and no agitation. The experiments were conducted at 274 K with initial gas pressure of 10 MPa. At a given SDS concentration, the gas-inducing agitation gave higher hydrate formation rate than normal agitation and no agitation. Gas inducing agitation of deionized water gave a relatively low methane hydrate formation rate, which could be greatly enhanced by adding SDS. The enhanced kinetics can be attributed to increased gas-liquid contact area, with the coalescence of induced gas bubbles being effectively inhibited by SDS at low concentrations.

Modeling of thermalization phenomena in coaxial plasma accelerators

Coaxial plasma accelerators are electromagnetic acceleration devices that employ a self-induced Lorentz force to produce collimated plasma jets with velocities ~50 km s−1. The accelerator operation is characterized by the formation of an ionization/thermalization zone near gas inlet of the device that continually processes the incoming neutral gas into a highly ionized thermal plasma. In this paper, we present a 1D non-equilibrium plasma model to resolve the plasma formation and the electron-heavy species thermalization phenomena that take place in the thermalization zone. The non-equilibrium model is based on a self-consistent multi-species continuum description of the plasma with finite-rate chemistry. The thermalization zone is modelled by tracking a 1D gas-bit as it convects down the device with an initial gas pressure of 1 atm. The thermalization process occurs in two stages. The first is a plasma production stage, associated with a rapid increase in the charged species number densities facilitated by cathode surface electron emission and volumetric production processes. The production stage results in the formation of a two-temperature plasma with electron energies of ~2.5 eV in a low temperature background gas of ~300 K. The second, a temperature equilibration stage, is characterized by the energy transfer between the electrons and heavy species. The characteristic length scale for thermalization is found to be comparable to axial length of the accelerator thus putting into question the equilibrium magnetohydrodynamics assumption used in modeling coaxial accelerators.

Consequences of a 12-mm diameter high pressure gas release on a buried pipeline. Experimental setup and results

When considering the transportation of gas through high pressure pipeline and associated permitting, the 12-mm diameter breach is one of those commonly considered as accidental scenarios and the associated consequences must to be calculated for determining the required safety measures. Up to now this “12-mm” scenario was modeled at the convenience of each risk analyst with no certitude on the real behaviour of the gas in the soil for these types of releases.To obtain concrete information on the “12-mm” scenario considered as the sizing event for safety distances associated to a little breach due to corrosion for instance, AIR LIQUIDE, ENGIE, NATIONAL GRID, PETROBRAS and TIGF decided to launch in 2013 a JIP (Joint Industrial Program) named “CRATER”. The aim of this project was to improve knowledge on the consequences of leakages occurring on buried high pressure pipes, and to determine what were their behaviour and their impact on the soil – i.e. crater formation, or not, according to release parameters – in order to use the appropriate methodology for risk and consequences assessment. Thus by changing several parameters – like nature of gas, initial gas pressure, type of soil … – the threshold between crater formation and gas dispersion in the soil following such leakages was investigated (specifically for methane and hydrogen, flammable and light gases). INERIS was chosen as subcontractor to perform nearly-full scale tests on its experimental site in order to collect reference data, understand phenomena and correctly assess the gas behaviour for accurate risk evaluation.