Variation Of Gas Pressure Research Articles

Fracture toughness measurements of soft sediments based on gas injection tests

The gas in soft cohesive sediments tends to transport through fractures or cracks, and the study on fracture toughness of soft soil is an important component of the research on gas migration. A method for measuring fracture toughness of soft sediments is proposed in this paper. The gas injection tests on soft soil at constant flow rate were conducted, and the fracture toughness of soft soil could be calculated combined with the theory of linear elastic fracture mechanics based on the gas pressure and the orifice diameter. Through direct observation of the bubble growth in Laponite RD transparent soil, the law of gas pressure variation and the mechanism of bubble fracture growth in soft soil were further verified. The methods and instruments proposed in this paper are convenient and easy for operating, which are suitable for measuring fracture toughness of soft soil in laboratory. The fracture toughness of soft soil obtained by the method presented in this paper is consistent with the measurements of the in-situ soft clay proposed in the literature, which suggests that the fracture toughness measurement method of soft soil proposed in this paper is reasonable.

Study on the pressure relief effect in gob‐side coal body during mining an inclined longwall panel

AbstractThis study combined multi‐field coupled numerical calculations and field measurements to analyze the gas pressure relief and the outburst elimination range of the coal body in the lower side of a gob induced by excavating an inclined seam. A coal seam gas flow solid‐gas coupled model allowing for elastoplastic damage was established based on an inclined longwall panel of the Hongyan Coal Mine in Chongqing, China. To inspect the gas depressurization effect, this study simulated the collapse and damage of strata surrounding the longwall panel after mining by using a constitutive model of the interlayer weak plane, the changes in the damage, gas pressure, and stress concentration in the gob‐side coal seam were analyzed numerically. Besides, variation in gas pressure within 10‐23 m away from the panel margin was measured on‐site during the advancement of the longwall face to validate and modify the results of modeling. The simulation results showed that the advancing of the panel is highly effective in releasing gas from the gob‐side coal body. The rupture penetration, stress concentration, and original elastic zone will be formed in the gob‐side coal body with increasing distance away from the gob after mining the 3603‐2 panel. The permeability increased dramatically and the gas was almost exhausted in the rupture penetration zone. The field measurement results indicated that gas pressure decreased in three stages with advancement. After completion of excavation activities, the drop rates of gas pressure and gas content within 10‐23 m from the gob were 26.55%‐73.58% and 34%‐71%, respectively. Additionally, it was proved that the numerical simulation results were instructive for predicting the range of gas outburst‐proneness elimination belt by comparing simulation and field results, and the outburst elimination range of the inclined longwall panel of the Hongyan Coal Mine was determined to be 10 m.

Simulation of gas transport in a landfill with layered new and old municipal solid waste

Average biodegradation rate of newly filled municipal solid waste (MSW) in landfills is relatively fast, and the landfill gas produced by the new MSW biodegradation can cause great variations in gas pressure. To predict the gas pressure distribution in the MSW layer, a one-dimensional gas transport model is established in this study. The following factors are considered in this model: (1) the variation of gas permeability with depth; (2) the anisotropy ratio of gas permeability; (3) the settlement caused by waste biodegradation. Furthermore, a single peak model for gas production is applied as the source term of gas production. The equation for settlement caused by waste biodegradation is presented, and the time of peak gas production rate is obtained by fitting the settlement of the newly filled layer. The stratification of the unsaturated and saturated regions is taken into account by distinguishing the difference in gas saturation. The layering of the new and old waste layers is considered by distinguishing the difference in the length of time that waste has been degraded to produce gas. Based on the method of numerical calculation, the gas pressure distribution in the landfill with layered new and old MSW is well simulated. The position where the maximum gas pressure occurs is found. The sensitivity analysis shows that the influence of the anisotropy ratio on gas pressure distribution is more significant.

Simultaneous measurement of effective thermal conductivity and effective thermal diffusivity of Li2TiO3 pebble bed using transient hot-wire technique

Lithium-based ceramics in the form of pebble beds have been considered for tritium breeder material in the fusion reactor's breeder blanket. It is essential to study the thermal characteristics of these ceramic pebble beds subjected to fusion relevant conditions. Effective thermal conductivity (k), effective thermal diffusivity (α) and effective specific heat (cp) of a packed bed are some of the crucial parameters for the design of breeder blanket module. In the present study, the transient hot-wire technique was used to measurek, α and cp of lithium metatitanate (Li2TiO3) pebble bed fabricated at Institute for Plasma Research, India. Thermal properties of Li2TiO3 pebble bed (1 ± 0.15 mm pebble diameter and ∼63% packing fraction) are measured within the temperature range of 45 °C to 800 °C in stagnant helium gas environment. The filling gas pressure variation effect on the Li2TiO3 pebble bed's thermal properties for the pressure range of 0.105 MPa to 0.4 MPa has also been studied. Equations are suggested for k and α of Li2TiO3 pebble bed as a function of temperature at different pressure in the helium gas environment.

Effects of ethanol port injection timing and delivery rate on combustion characteristic of a heavy-duty V-12 diesel engine

Using biobased fuels in Diesel engines is an effective solution reduce the generation of toxic components in the exhaust gas. One of them, alcohol, is the potential fuel to reduce emissions and dependence on fossil fuels. So, this study is aimed to investigate the effects of ethanol port injection timing and delivery rate on the combustion characteristic of a heavy-duty V-12 Diesel engine when ethanol substitution percentage is 30% to reach the original diesel quantity at full load. The combustion characteristic analysis indicates that the variation in cylinder gas pressure and temperature decreases when retarded ethanol injection timing and decreased ethanol delivery rate, the engine works more smoothly due to the maximum rate of pressure rise decreases. However, the changes are greater when changing the ethanol injection timing as compared to ethanol delivery rate case.

Tunable surface plasmon resonance in laser-induced plasma spheroids

We present a study of the Ku-band tunability of the surface plasmon response of a gaseous plasma resonator generated by laser-induced gas breakdown. Tuning is achieved by varying gas pressure and laser pulse energy. Microwave scattering characteristics of the plasma resonator are obtained using an experimental configuration in which a waveguide is loaded with a single plasma element. Optical imaging of the laser plasma is used to characterize the time-dependent plasma size. Complex transmission waveforms are attributed to the dynamic expansion of the plasma, resulting first in a sweep through the principle Mie resonance, followed by strong reflection of the incident wave due to bulk plasma loading as the plasma expands to significantly fill the waveguide. The described resonator has the potential to be used in an all-plasma metamaterial with tunable opacity and resonance frequency.

A novel solar-powered self-blowing air heating system with active control based on a quasi-Stirling cycle

In this paper, a novel active solar heating system with self-blowing capability based on a quasi-Stirling cycle is modeled, developed, and primarily tested. First, the working principle of the proposed heating system is described and the possibility of power generation for air blowing based on the quasi-Stirling cycle is discussed. Then, a dynamic model for the proposed system is presented. Next, the presented mathematical model is used to simulate the system performance as well as to tune the control unit to acive the desired performance. Accordingly, the variations of gas pressure, temperature, and airflow rate over a working cycle are simulated through which the generated heat and power of the system can be evaluated. Finally, the experimental rig is developed and experimented. It is found that the proposed cogeneration system provides the ventilating air at a temperature of 333 K and an average airflow rate of 0.00994 m3/s besides the output work of 490 J in each working cycle practically. Moreover, the obtained experimental data from this first-stage developed technology reveal the feasibility of the presented idea, which can be further extended in the next stages of its development including design optimization, scalability, exergy analysis, and applicability in real fields.

Effect of ambient pressure on gas adsorption characteristics of residual coal in abandoned underground coal mines

To study the influence of ambient pressure on gas adsorption of residual coal and provide a basis for establishing a reasonable calculation model of gas resource adsorbed in residual coal in abandoned underground coal mines, the residual coal was divided into loose-type residual coal and column-type residual coal after an analysis on the ambient gas pressure variation process. Then the gas adsorption experiments were conducted under adsorption equilibrium pressure range of 0.5–2.5 MPa using a self-made experimental device. The results show that (1) In the range of 0.5–2.5 MPa, the amount of methane adsorption in the loose-type residual coal under the intense replenishment condition can be 19.5% less than that under the gradual replenishment condition. (2) With a continuous decrease in ambient pressure, the methane adsorption amount in the column-type coal is reduced. The adsorption capacity at a unit pressure drop gradually increases from a minimum of 0.24 mL▪g-1 × 0.1 MPa−1 to a maximum of 2.375 mL▪g-1× 0.1 MPa−1. The initial adsorption equilibrium pressure shows little effect on the methane adsorption in column-type residual coal. (3) The bigger difference of the methane adsorption amount, with a maximum of 2.347 mL▪g-1, between the loose-type residual coal and column-type residual coal under the intense replenishment condition can be observed in the pressure range of 0.8–1.2 MPa. Therefore, the coal type should be considered to establish a gas storage model of residual coal in abandoned coal mines.

Low-inertia method of control over nitrogen concentration in the PVD nitride coatings by non-self-sustained arc discharge with thermionic and hollow cathodes

Using the probe technique, a comparative analysis of parameters of the gas-metal plasma generated by low-pressure discharges is performed during variation of their main characteristics. It is shown that by varying the discharge current of the gas plasma source it is possible to readily change the fraction of gas ions in the gas-metal plasma generated by the arc evaporator and the gas plasma source with thermionic and hollow cathodes. In the case of nitride coatings, it is found out that the concentration of nitrogen in the coatings formed by the vacuum-arc plasma-assisted deposition increases, without any changes in the nitrogen working pressure. Using the coatings based on the Mo–N and Ti–N systems as examples, a twofold increase in the nitrogen concentration is shown as the ion current density of the gas plasma source increases by a factor of three in comparison with the modes without using this source. The method discussed in this study exhibits lower inertia compared to the traditional gas pressure variation.

Simulation on the dynamic variation of downhole gas pressure during deflagration fracturing in screen completed well

Deflagration fracturing technique also named high energy gas fracturing (HEGF) technique was applied for creating several radial fractures nearby the wellbore to improve the conductivity. Because of the good applicability for different reservoirs, deflagration fracturing technique was also tried in a screen completed well. However, the theoretical literatures about deflagration fracturing were mainly focused on the open-hole completed or perforated well. A simulation on the dynamic variation of gas pressure in screen completed well was required to avoid destroying the tool because of the structural difference between the screen pipe and casing tube. A model describing the deflagration fracturing process in screen completed well was built. Except for the traditional equations for a perforated well, an equation for the propellant burning, that for the displacement of pressurized liquid column with downhole pipe string operating, and that for the fluid flow through the screen pipe was introduced. Then, a numerical simulation was carried out to validate. Compared with the real production-increasing ratio, the simulated accuracy approached 90%. The calculated maximum pressure was 50.3 MPa when a simulation was done with the given parameters, in accordance with the safety command of screen completed well. The maximum gas pressure had decreased with the increase of hole density and size of the screen pipe. A suggestion for operating pipe during deflagration fracturing was given. Operation with a downhole pipe string of large size and large wall thickness was beneficial for the safety during fracturing process.

Experimental Research on Coal and Gas Delay Outburst and AE Characteristics under Conditions of Geostress and Gas Pressure Disturbance

Adopting yellow mud as barrier layer materials, coal and gas delay outburst experiments under conditions of geostress and gas accumulation disturbance were carried out by using self‐developed simulation system, to find out roles of geostress and gas pressure played in the process of the delay outburst and ways to predict it, through analysis of variations of gas pressure, and AE characteristics during the process. The results show that after the geostress increased by 0.11 MPa from 1.80 MPa, an outburst occurs, while in gas accumulation situations, the gas pressure increase of 0.27 MPa from 0.67 MPa induces an outburst; hence, geostress is one of the dominant factors impacting an outburst occurrence. The lasting time of the outburst triggering under geostress disturbance is shorter than that under gas accumulation disturbance, while the duration of the outburst development under gas accumulation conditions is longer than that under geostress conditions. Coal seam breakage by geostress is the precondition for an outburst risk, and gas expansion energy is the dominant parameter influencing the duration of the outburst development. The AE signals show distinctive features in different stages of the outburst under geostress disturbance. At the preparation stage of the outburst, the AE signals increase sharply but have a low intensity and then drop to a lower balance level. At the triggering stage, the AE signals become active and increasing until up to the peak where the outburst occurs, and the intensity is highest.

A simple method to calibrate the temperature effect for the calculation of gas permeability

Temperature plays an important role in the gas permeability test. A small temperature variation still exists in the experimental process since the temperature control device cannot strictly maintain a constant temperature. This can further affect the accuracy of the gas permeability. To solve this problem, a simple method based on the ideal gas equation of state is introduced to calibrate the gas pressure variation because of the temperature effect. We verified the calibration results through sever?al examples, and the results proved the feasibility and effectiveness of the method. In particular, this method is particularly effective for low permeability materials in long-term gas permeation tests.

Effects of misfire on the dynamic behavior of gasoline Engine Crankshafts

Misfire faults caused by the malfunction of single cylinder increases the emission level and fuel consumption of internal combustion. So, the detection of misfire is required.In this paper, we studied the effect of misfire on the dynamic response of the crankshaft in order to propose a method based on the torsional vibration signal of crankshaft acceleration for misfire detection. For this, a torsional model of a four cylinder crankshaft excited by the acyclism phenomena is proposed. The external forces are the inertia and gas torque of each engine cylinder. The equations of motion are obtained by using Lagrange method and computed with the help of Newmark algorithm. Three kind of misfire faults of the first cylinder are modeled through the gas pressure variation inside this cylinder and induced in the excitation torques: missing combustion, pre-ignition and delayed ignition. After that, the vibration responses of the crankshaft is computed and processed in order to highlight the effect of misfire defects on the crankshaft vibration signals. In fact, appearance of sidebands around the acyclism frequency in the frequency domain allow detecting the misfire and the time acceleration signal allows identifying the kind of defect.

Configurational Entropy Driven High-Pressure Behaviour of a Flexible Metal-Organic Framework (MOF).

Flexible metal–organic frameworks (MOFs) show large structural flexibility as a function of temperature or (gas)pressure variation, a fascinating property of high technological and scientific relevance. The targeted design of flexible MOFs demands control over the macroscopic thermodynamics as determined by microscopic chemical interactions and remains an open challenge. Herein we apply high‐pressure powder X‐ray diffraction and molecular dynamics simulations to gain insight into the microscopic chemical factors that determine the high‐pressure macroscopic thermodynamics of two flexible pillared‐layer MOFs. For the first time we identify configurational entropy that originates from side‐chain modifications of the linker as the key factor determining the thermodynamics in a flexible MOF. The study shows that configurational entropy is an important yet largely overlooked parameter, providing an intriguing perspective of how to chemically access the underlying free energy landscape in MOFs.

Configurational Entropy Driven High‐Pressure Behaviour of a Flexible Metal–Organic Framework (MOF)

AbstractFlexible metal–organic frameworks (MOFs) show large structural flexibility as a function of temperature or (gas)pressure variation, a fascinating property of high technological and scientific relevance. The targeted design of flexible MOFs demands control over the macroscopic thermodynamics as determined by microscopic chemical interactions and remains an open challenge. Herein we apply high‐pressure powder X‐ray diffraction and molecular dynamics simulations to gain insight into the microscopic chemical factors that determine the high‐pressure macroscopic thermodynamics of two flexible pillared‐layer MOFs. For the first time we identify configurational entropy that originates from side‐chain modifications of the linker as the key factor determining the thermodynamics in a flexible MOF. The study shows that configurational entropy is an important yet largely overlooked parameter, providing an intriguing perspective of how to chemically access the underlying free energy landscape in MOFs.

Molecular Diffusion in a Flexible Mesoporous Metal–Organic Framework over the Course of Structural Contraction

In situ 1H pulsed field gradient (PFG) NMR was used to investigate the molecular diffusion of n-butane in the pores of the flexible metal–organic framework DUT-49(Cu) at 298 K at different pore loadings, including pressure ranges below and above the negative gas adsorption (NGA) transition caused by structural contraction of the material. Supported by molecular dynamics simulations, the investigation provided crucial insight into confined diffusion within a highly flexible pore environment. The self-diffusion coefficients were derived from the experiment and compared with simulations, capturing the diffusion during n-butane adsorption and desorption. This complementary approach has yielded experimental characterization of molecular diffusion mechanisms during the unique process of NGA. This includes the observation of a 4-fold decrease of diffusivity within a less than 2 kPa gas pressure variation, corresponding to the NGA transition point.

Plasma Characterization Using a Silicon-Based Terahertz Frequency Comb Radiator

In this letter, temporal evolution of plasma density is characterized in the time-domain using a low-power THz frequency-comb radiator in the 130-nm SiGe BiCMOS process. The frequency-comb radiator covers from 10 s of GHz up to 1.1 THz where the spacing between tones is programmable and can be set by the frequency of an external trigger signal to as high as 10.5 GHz. Due to the complex permittivity of plasma, electromagnetic waves experience a phase and amplitude change as they pass through the plasma. The THz-pulse radiator used in this letter is locked to a low-phase noise external source. Hence, the phase-noise of the radiated tones is extremely low, which enables detecting small phase changes. In this measurement, phase and amplitude changes of THz waves are captured from 333 to 495 GHz for different plasma parameters by varying gas pressure, plasma pulse rate, and plasma excitation power.

나노 다공성 멤브레인의 통과 기체 압력 패턴 및 압력 변화 패턴 분석을 통한 물질 특성 판별에 관한 연구

최근 배터리 분리막, 가스 분리, 항균 필터 등의 기술을 필요로 하는 산업들이 크게 발전함에 따라 우수한 관련 특성을 지닌 나노 다공성 물질이 주목을 받고 있다. 소재의 독특한 특성과 높은 산업적 활용도 덕분에 나노 다공성 물질과 관련된 많은 논문들이 발표되고 있다. 그러나 다뤄지는 나노 다공성 물질들의 특성을 비파괴적으로 빠르게 분석할 수 있는 방법은 거의 없다. 본 논문에서는 나노 다공성 멤브레인을 대기가 통과했을 시 형성되는 압력 변화 패턴을 분석하여 소재의 특성을 비파괴적이면서 고속으로 분석할 수 있는 방법을 제시한다. 대기가 나노 다공성 멤브레인을 통과할 시, 멤브레인 고유의 구조와 요소들로 인해 기체 분자의 에너지 손실이 멤브레인별로 다르게 발생한다. 이러한 기체의 에너지 손실은 압력 강하, 낮은 압력 변화치 등의 현상의 원인이 되어 결과적으로 고유의 압력 패턴을 만들어낸다. 본 논문의 결과는 대기가 멤브레인을 통과할 시 만들어지는 고유 압력 패턴을 통해 다공성 나노 소재의 특성 파악 및 물질 판별이 가능하다는 점을 제시하고 있다.

Partial Discharge Behaviour of a Protrusion in Gas-Insulated Systems under DC Voltage Stress

High reliability, independence from environmental conditions, and the compact design of gas-insulated systems will lead to a wide application in future high voltage direct current (HVDC) transmission systems. Reliable operation of these assets can be ensured by applying meaningful and robust partial discharge diagnosis during development tests, acceptance tests, or operation. Therefore, the discharge behavior must be well understood. This paper aims to contribute to this understanding by investigating the partial discharge behavior of a distorted weakly inhomogeneous electrode arrangement in sulfur hexafluoride (SF6) and synthetic air under high DC voltage stress. In order to get a better understanding, the partial discharge current is measured under the variation of the insulation gas pressure, the gas type, the electric field strength, and the voltage polarity. Derived from this, a classification of the different discharge types is performed. As a result, four different discharge types can be categorized depending on the experimental parameters: discharge impulses, discharge impulses with superimposed pulseless discharges, discharge impulses with superimposed pulseless discharges, and subsequent smaller discharges and pulseless discharges. Concluding suggestions for partial discharge measurements under DC voltage stress are given: recommendations for the necessary measurement time, the applied voltage and polarity, and useful measurement techniques.

Modeling of Coal Matrix Apparent Strains for Sorbing Gases Using a Transversely Isotropic Approach

Gas sorption-induced coal deformation is one of the primary geomechanics effect in coalbed methane (CBM) engineering. Coal is known to have transversely isotropic properties because of its cleat structure. We propose a new theoretical approach to modeling the strain behavior of bulk coal by including sorption-induced matrix shrinkage/swelling strain, cleat volume strain and matrix mechanical strain resulting from changes in pore pressure, and external stresses. The new model framework can define the apparent bulk coal volume with respect to the variation in gas pressure. To validate the model, unconstrained gas flooding experiments were conducted with helium, methane and carbon dioxide injections. The experimental data agreed well with the modeled strain evolution results under hydrostatic conditions and at the injection pressure conditions. The results show that the degree of anisotropy is ~ 1.6 for helium injection, comparing the strains perpendicular to and parallel to the bedding plane. The results demonstrate that the volumetric strains closely correlate to the sorption capability of coal. The maximum volumetric strain induced by carbon dioxide injection can reach ~ 2.05% as gas pressure increases up to ~ 5.43 MPa, which is ~ 2.77 times that of the methane-induced volumetric strain of ~ 0.74% at a gas pressure of ~ 5.45 MPa. The proposed model can be simplified to be equivalent to the commonly extended Langmuir-type strain model at relatively low gas pressure for bulk coal with low cleat porosity. The proposed model can also successfully cover the volumetric response of bulk coal for high pressures that range beyond 13 MPa. A sensitivity study shows that Young’s modulus, Poisson’s ratio, and the degree of anisotropy affect the volumetric responses differently at various pressure stages, but the effects are always distinct for high-pressure injections. The proposed model framework can be coupled into a coal dynamic permeability model for defining the permeability evolution—which is important for gas production predictions for CBM wells.