Variation Of Gas Pressure Research Articles

Investigation into Gas Pressure Variation at Inlet of a Converging-Diverging Nozzle

Investigation into Gas Pressure Variation at Inlet of a Converging-Diverging Nozzle

Gas Network Development in Compact Bentonite: Key Controls on the Stability of Flow Pathways

Compacted bentonite is proposed as an engineered barrier material within facilities for the geological disposal of radioactive waste. Barrier performance and its interaction with a free gas phase must be considered as part of sound repository design. This study involved the long-term experimental examination of gas flow in precompacted bentonite, with particular consideration of gas network stability. Results demonstrate that the stress field experienced by the clay is strongly coupled with gas flow. For the first time, three controls on this behaviour are considered: (i) injection flow rate, (ii) constant vs. variable gas pressure, and (iii) stimulation of the microfracture network. A detailed stress analysis is used to examine changes in the gas flow network. The results indicate a degree of metastability despite these changes, except in the case of stimulation of the microfracture network by removal of the primary drainage route. In this case, a rapid redevelopment of the gas flow network was observed. As such, availability of drainage pathways will represent a key control on the generation of peak gas pressures and distribution of gas within the engineered barrier. The cessation of gas flow is shown to result in crack closure and self-sealing. Observations from this study highlight that characterisation of the gas network distribution is of fundamental importance in predicting gas dissipation rates and understanding the long-term fate of gas in radioactive waste repositories.

Water quality and solute sources in the Marsyangdi River system of Higher Himalayan range (West-Central Nepal)

Surface waters, cold and hot springs were collected in different catchments along the Marsyangdi basin, in the Himalayan Range of West-Central Nepal, during the post-monsoon season in 2017 and analyzed for major ions and trace elements, with the aim of assessing the sources of dissolved species and to contribute in watershed planning. The major element data indicate that surface waters coming from the Tethyan Himalayan Sequence (THS) range from the Ca-Mg-HCO3 to the Ca-Mg-HCO3-SO4 water-types and reflect a two-component mixing of waters from carbonate- and sulfate-bearing sources. The latter component is attributable to sulfide oxidation with minor silicate weathering. In the Greater Himalaya Sequence (GHS), alteration of pedogenetic carbonates formed in response to silicate weathering under a variable CO2 gas pressure dominates, yielding a Ca-HCO3 signature. The stability diagram in the K2O-Al2O3-SiO2-H2O system and the paired increases in Ca2+, Na+, K+ and silica indicate that degradation of silicate minerals through kaolinization and possibly plagioclase albitization reactions is the main process for hot groundwater. Cold and hot springs define a trend of increasing Li, SiO2 and Cl−, suggesting that lithium was leached from silica-rich sources, such as pegmatite dykes and sills occurring in host rocks, and concentrated into halite-bearing salt aquifers. In hot waters Sb, As and Tl exceed the EU and USEPA thresholds. Tl is usually incorporated into pyrite and correlates with Li indicating the occurrence of an ore-bearing zone possibly related to hydrothermal activity at the transition zone between THS and GHS, as suggested by the relatively high Ba, Ni, Cu, Sb, As and Mn contents. The obtained data on water quality have significant implications for people living along the Upper Marsyangdi River in the management of water resources, especially in terms of the enhancement of cold water aquaculture and hot water uses for recreation purposes and tourism.

TNT equivalency in an internal explosion event.

The peak gas pressure developed as a result of a confined explosion is an important parameter characterizing the pressure signal and is crucial for assessment of the structural response of the confined space envelope elements. The gas pressure depends on the amount of the released energy, including the afterburning energy. A new analytical model is presented to predict the gas pressure developed in a confined volume, for different types of explosives, as function of the charge weight (W) and the free confined volume (V), considering the afterburning effect. The model is based on the detonation chemical reaction and on the calculation of a full or partial afterburning energy release due to the reaction of the fuels in the detonation products with the surrounding oxygen. Considering the detonation energy and the possible additional afterburning energy, the model demonstrates the different behavior of the gas pressure variation with W/V for different types of explosives. The equivalent TNT charge weight is calculated for each explosive. According to the analysis performed, the TNT equivalent factor varies with W/V. The predictions of the model results are compared with available models as well as with available test data and very good agreement is obtained.

Fabrication of dual-parameter fiber-optic sensor by cascading FBG with FPI for simultaneous measurement of temperature and gas pressure

A dual-parameter fiber-optic sensor based on fiber Bragg grating (FBG) cascaded with Fabry–Pérot interferometer (FPI) structure is described and demonstrated to measure temperature and gas pressure simultaneously. The proposed sensing structure consists of an extrinsic FPI in the form of hemispherical ultraviolet (UV) curing glue capped on a FBG end face. The spectral interference peak produced by the UV glue FPI is sensitive to ambient temperature and gas pressure variations, whereas the reflection spectrum of FBG only depends on temperature and insensitive to pressure change, therefore, the temperature and gas pressure can be simultaneously measured by this cascaded sensor. Experimental results show that the sensor has higher temperature and gas pressure sensitivities of 223.4 pm/° C and 24.99 nm/MPa in a range from 30 ∘C to 110 ∘C and from 0.1 MPa to 0.7 MPa. Utilizing the temperature-dependent sensitivity of FBG, a constructed sensitivity matrix is used to distinguish measurement of temperature and gas pressure, and the measurement resolutions are determined to be 0.086 ∘C and 0.730 KPa. This sensing architecture is not only an effective method for single-point multi-parameter measurement, but also has merits of high sensitivity, compactness, ease of fabrication and low cost, which make it valuable for biosensors and medical applications.

The effect of adsorption-induced swelling on porosity based on the transient coal swelling model

Coal swelling induced by gas adsorption is a well-known phenomenon. In order to enhance coalbed methane production and greenhouse gases sequestration, adsorption phase should be understood deeply, and it is the most basic and the most important. Experimental measurements performed in this work on three samples from Kaiping Basin using carbon dioxide. Basing on Gibbs adsorption model, the steady-state swelling model is developed, which also assume that the change of the coal surface free energy induced by adsorption is equal to the change of energy caused by adsorption deformation. The mass balance equation of gas in porous media is combined with the steady-state swelling model. The dynamic variation of porosity and internal gas pressure of coal are integrated into the transient swelling model. The steady-state model and transient model are applied to describe the experimental volumetric strain. The results show good agreement between the models and the experimental strain data. The coal pore tests with different probe scales are also used to investigate the true pore size distribution and porosity, which provide more accurate parameter values. According to the transient swelling model, the effects of porosity on adsorption-induced swelling are further analyzed.

Изменение элементного состава тонких пленок цирконата-титаната свинца в процессе ионно-плазменного осаждения: эксперимент и моделирование

AbstractThe element composition modification is experimentally studied in PZT thin films obtained via the RF magnetron sputtering with variable working gas pressure. The experimental data were interpreted through the statistic simulation of thermalization and diffusion of sprayed Pb, Zr, and Ti atoms during the ion-plasma deposition of PZT thin films. The simulation data are shown to adequately describe (within the limits of 5%) the change in element composition at various pressures of the gas environment. The study conducted enables one to produce PZT thin films with a set element composition, which is essential for optimizing the electric and physical properties of solid solutions at the morphotropic phase boundary.

Application of Hydraulic Flushing in Coal Seams To Reduce Hazardous Outbursts in the Mengjin Mine, China

Abstract Hydraulic fracturing and waterjet slotting fracturing have been demonstrated to be effective in creating artificial fractures and stimulating gas production in hard coal seams. However, these methods are inefficient for soft-outburst coal seams because these created fractures are short and easy to close. To eliminate the outburst risk of soft coals, a novel enhanced coalbed methane under-panel cross-strata drainage technique via hydraulic flushing was proposed in this work. The hydraulic flushing effects of boreholes of different sizes in the coal seam were also pre-evaluated by a simulation approach. The modeling results indicate that as the radius of the borehole increases, the plastic and stress-decreasing zone expands. A field test was also conducted in the Minjin mine, China, that investigated the gas pressure variation between three monitoring boreholes at different distances from a hydraulic flushing borehole. Test results indicate that the effective influence radius of gas extraction is approximately 5.5 m. Based on the results of the field test and borehole camera observation, the unloaded coal quantity and the average diameter of the boreholes were estimated to be 8.0 t and 942 mm, respectively. The borehole diameter expanded up to 10 times larger than its original size. The average gas extraction concentration and gas flow rate increased by approximately 2 and 3.5 times, respectively, demonstrating the effectiveness of the proposed hydraulic flushing in improving the gas extraction efficiency. The hydraulic flushing technique therefore is proved to be efficient in eliminating the outburst risk of coal and reducing greenhouse gas emissions.

Photophoretic force measurement on microparticles in binary complex plasmas

This article presents a method to measure the photophoretic force on microparticles in complex plasmas. A laser heating setup is used to increase the kinetic temperatures of binary mixtures composed of melamine-formaldehyde (MF) and silica (SiO2) particles. The temperature gain of both particle species due to the additional thermal reservoir is compared to a laser force model. Contributions of radiation pressure and photophoretic forces are determined through a variation of neutral gas pressure and application of Lorenz-Mie theory. The photophoretic force is found to be significant for MF particles at typical conditions in complex plasma experiments.

Temperature and Gas Pressure Monitoring and Leachate Pumping Tests in a Newly Filled MSW Layer of a Landfill

Field test data on the simultaneous variations of leachate level, temperature and gas pressure in waste can be used in verifying the theoretical solution of coupled model of gas pressure and temperature in municipal solid waste (MSW) landfills. The correlation between the variations of these properties caused by leachate pumping is a major concern in the management of landfills. Therefore, temperature and gas pressure monitoring and leachate pumping tests were conducted in a newly filled MSW layer of a landfill located at Wuxi, southeastern China. The multifunctional extraction well and monitoring wells were designed to monitor the simultaneous variations of leachate level, temperature and gas pressure. The spatial and temporal distributions of these parameters and their correlation were investigated and analyzed. The results show that the highest waste temperature occurs near the leachate level. The gas pressures measured in the waste above the leachate level increase with depth. During the leachate pumping test, the temperature and gas pressure increase in the leachate level decreasing zone. When the leachate level has stably recovered, the temperature decreases slightly and gas pressure in this zone decreases to nearly zero. In addition, the MSW permeability of the newly filled MSW layer is calculated. The variation in the water content caused by the change in the leachate level affected the temperature and gas pressure in the waste. The temperature and gas pressure increased in the leachate level decreasing zone. The gas pressure was collectively affected by the water content and temperature in the waste.

Energy consumption investigation of electromagnetic valve train at gas pressure conditions

Electromagnetic valve train (EMVT) shows enormous potential for the improvement of IC engine thermal efficiency. The combustion gas pressure is one of challenges with EMVT applied to exhaust system, which makes serious disturbances to the opening performance and increases the energy consumption of EMVT. Therefore, coupled models between mathematical model of EMVT and engine thermodynamic model are carried out to study the effect of combustion gas pressure on EMVT. The experiments are established based on electromagnetic linear load simulator innovatively, which has fast dynamic response and high loading precision. With the electromagnetic linear load simulator, realistic combustion gas pressure conditions can be produced accurately. Simulation and experimental results show robust valve opening performance for large variations in combustion gas pressure, and the opening transition time keeps a constant of 3 ms at different gas pressure conditions, but the valve opening has a delay of 0.2 ms per 0.1 MPa. Further, we get the conclusion that gas pressure would cause an increase of EMVT’s energy consumption. At the condition of 0.6 MPa gas pressure, energy consumption has an increase of 85.6%, which mainly embodies in the differential pressure loss and increase of copper loss, while the iron loss and mechanical loss remains approximately constants.

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.

Evaluating microgap breakdown mode transition with electric field non-uniformity

This paper evaluates the transitions between the breakdown modes that are dominated by field emission (FE) and by secondary electron emission (SEE) in argon microgaps, based on a mathematical model originally proposed for the modified Paschen’s curve (Go and Pohlman 2010 J. Appl. Phys. 107 103303). In the present model, instead of assuming a constant electric field across the gap, the spatial distribution of the electric field due to the presence of a parabolic cathode protrusion is implemented, and a modification of the first Townsend ionization coefficient for microscale gaps from particle-in-cell/Monte Carlo collision simulations is employed (Venkattraman and Alexeenko 2012 Phys. Plasmas 19 123515). The breakdown mode transitions are quantified by the variations of gas pressure and gap distance. It is found that assuming a constant electric field across the gap will overestimate the electron avalanche, which underestimates the breakdown voltage and shifts the breakdown mode transitions to a smaller gap. By varying the field enhancement factor, the critical point of the breakdown mode transition can be significantly adjusted. Increasing the field enhancement factor will lower the breakdown voltage in the FE regime and increase the breakdown voltage in the SEE regime.

Pressure optimization and phase matching of high harmonics generation in CO2 and C2H2 molecular gases

We experimentally investigate the effect of the varying gas pressure on high harmonic generation (HHG) in carbon dioxide (CO2) and acetylene (C2H2) gases with femtosecond laser fields. The pressure variations cause changes of the concentration of gas molecules and also affect the phase matching conditions and absorption. The experimental results have demonstrated appearance of well pronounced peaks of the yields of high harmonics at certain pressure values maximizing the coherence length of HHG and were confirmed with the theoretical calculations based on one-dimensional model, providing good agreement.

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.

Experimental study on radon exhalation characteristics of coal samples under varying gas pressures

Abstract Coal and gas outburst during underground mining operations negatively affects the mining safety and decrease the mining productivity. Current outburst prediction has been largely relying on seismic monitoring which is passive and extremely difficult to quantify. As coal produces radon in the damage process, this unique feature potentially offer a new way to reliably predict the outburst incidents. Therefore, in this study, a series of experiments were carried out under different gas pressures adopting the new coal-rock triaxial-loading radon exhalation test system, which aim to investigate the effect of gas depletion pressures on the characteristics of radon exhalation. The data of stress-strain, radon concentration, and acoustic emission were monitored simultaneously in the dynamic loading processes, and were compared and discussed in detail. Experimental results show that in the loading process, radon concentration shows clear step changes and has good consistency with the results of the coal deformation stages according to the acoustic emission count, verifying the feasibility of coal deformation and fracturing prediction based on radon concentration. Meanwhile, at the early stage of loading, the peak value of radon concentration reduces gradually with the increase in gas pressure. Furthermore, relationship between the maximum value of radon concentration and gas pressure is obtained. This work presents a new method to link gas pressure, coal deformation and fracture prediction together based on radon concentration, which could provide significant guidance for the accurate prediction of coal and rock dynamic disasters.

An experimental investigation of the roles of water content and gas decompression rate for outburst in coal briquettes

The coal and gas outburst has become a worldwide challenge and is still not fully understood. In this study, an experimental investigation was carried out for outburst evolution. Coal briquettes were fabricated based on less than 0.6 mm pulverized coal particles of Tunliu Coal Mine. CO2 was used to simulate outbursts by saturating coal briquettes in varying gas pressures (0.2, 0.4 and 0.6 MPa). The outbursts of coal briquettes were induced when rapid gas decompression was performed. The results indicate the outbursts depend on the gas pressure, water content and the rate of gas decompression. The differential pressure between the gas inside and outside the coal briquette is essential to outbursts and varies for different water contents while other parameters affect the initiation and intensity of outbursts as well. The higher gas pressure the more intense outburst occurs. It is worth noting that low rate of gas decompression cannot activate any outburst in the experiments even for a high gas pressure. The water content affects the outburst strongly. The critical minimum gas pressure in the coal briquettes with high water content becomes much higher than that in the coal briquettes with low water content. The major energy of the outbursts in the experiments is the expansion energy of the free state gas inside the coal briquettes. This study clearly demonstrates the progressive fragmentation of outbursts due to gas decompression.

On the Numerical Robustness of the Streaming Instability: Particle Concentration and Gas Dynamics in Protoplanetary Disks

Abstract The streaming instability (SI) is a mechanism to concentrate solids in protoplanetary disks. Nonlinear particle clumping from the SI can trigger gravitational collapse into planetesimals. To better understand the numerical robustness of the SI, we perform a suite of vertically stratified 3D simulations with fixed physical parameters known to produce strong clumping. We vary the numerical implementation, namely, the computational domain size and the vertical boundary conditions (vBCs), comparing newly implemented outflow vBCs to the previously used periodic and reflecting vBCs. We find strong particle clumping by the SI is mostly independent of the vBCs. However, peak particle densities are higher in larger simulation domains due to a larger particle mass reservoir. We report SI-triggered zonal flows, i.e., azimuthally banded radial variations of gas pressure. These structures have low amplitudes, insufficient to halt particle radial drift, confirming that particle trapping in gas pressure maxima is not the mechanism of the SI. We find that outflow vBCs produce artificially large gas outflow rates at vertical boundaries. However, the outflow vBCs reduce artificial reflections at vertical boundaries, allowing more particle sedimentation, and showing less temporal variation and better convergence with box size. The radial spacing of dense particle filaments is ∼0.15 gas scale heights (H) for all vBCs, which sets the feeding zone for planetesimal growth in self-gravitating simulations. Our results validate the use of the outflow vBCs in SI simulations, even with vertical boundaries close (≤0.4H) to the disk midplane. Overall, our study demonstrates the numerical robustness of nonlinear particle clumping by the SI.

Growth of AlN Crystal Using Reactive Sputtering Method With Variation of Nitrogen Gas Pressure and Substrate Temperature

Today’s semi-conductor technology continues to develop, both in terms of material discovery, manufacturing technique, as well as implementation and the development. In this research, the researcher will utilize the AlN synthesis with a reactive sputtering method on the substrate SiO2 that has done with variation substrate temperature of (200, 250, 300 o C), and the nitrogen gas pressure of 10, 15 and 20 mBar. This study successfully synthesize nanomaterial AlN with a hexagonal crystal system and shows the wurtzite phase is formed. While morphology AlN formed composed of particles - spherical shaped particles. From this research it is known that raising the temperature of the substrate produces more uniform morphology and homogeneous, the surface roughness is formed from 15,4 to 84 nm and obtained the crystal size is 64-87 nm. While the addition of nitrogen gas pressure causes the better crystallinity. The research obtained AlN with Optical Transversal wave type at a wavenumber of 600-670 cm-1. While the growth of AlN crystal growth of AlN is best obtained on the parameters of the substrate temperature 290 °C and nitrogen gas pressure of 20 mbar.

Investigation of Electron Beam Generation in Pseudospark Discharge-Based Plasma Cathode Electron Source

In this paper, an investigation has been carried out for the generation of electron beam in the pseudospark discharge-based plasma cathode electron (PD-PCE) source for a wide range of geometrical and operating parameters, such as cathode aperture, gas pressure, and seed electron energy, using 2-D kinetic plasma simulation code. It has been observed that the peak electron beam current’s time to appear at the anode surface decreases with an increase in the cathode aperture size, gas pressure, and injected seed electron energy. Investigation of the peak electron beam current and its time to appear at the anode is presented with reference to the variation of cathode aperture and gas pressure. It has been found that the generated electron beam current increases with increase in gas pressure while decreases with increase in the cathode aperture. The potential profile is also presented which is responsible for confinement of the plasma inside the hollow cathode (HC) cavity. The simulation has been performed for the required aperture size 2–10 mm, argon gas pressure 20–80 Pa, and seed electron energy 1–4 kV. The gas pressure, cathode aperture, and seed electron energy strongly influence the growth of plasma inside the HC cavity and also the generation of corresponding energetic electron beam. As a result, electron beams of different current amplitudes, sizes, and energies can be realized by proper control of the gas pressure, cathode aperture size, and seed electron energy of PD-PCE source for its use in extreme ultraviolet/X-ray and microwave applications.