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Sensitivity in polymer-bonded explosives (PBXs) relies on the presence of defects, such as cracks and voids, which create localized thermal energy, commonly known as hotspots, and initiate reactions through various localization phenomena. Our prior research has explored the use of internal gas pressure induced by thermite ignition to generate localized defects for PBX sensitization. However, further research is required to gain a more comprehensive understanding of the defect generation process resulting from internal gas pressure. This study investigates the process of defect generation in PBXs in response to internally induced gas pressure by applying controlled compressed gas to a fabricated cavity within the materials, simulating the gas pressure emitting from thermite. X-ray micro-computed tomography was employed to visualize the microstructure of the sample before and after gas injection. The experiments reveal the significance of gas pressure, cavity shape, temperature, and specimen compaction pressure in the defect generation. Numerical simulations using Abaqus/Standard were conducted to assess the defect generation in mock PBXs under varying gas pressures, cohesive properties, and binder thicknesses. The simulation results demonstrate the substantial influence of these properties on the ability to generate defects in mock PBXs. This study contributes to a better understanding of the factors influencing defect generation in mock PBXs. This knowledge is crucial for achieving precise control over defect generation, leading to improved ignition and detonation characteristics in PBXs. [ABSTRACT FROM AUTHOR]

Current commercial and in-house numerical simulators often employ discrete fracture models (DFM) and embedded discrete fracture models (EDFM) for flow simulation in fractured reservoirs. However, a generic projection-based embedded discrete fracture model (pEDFM), which outperforms both DFM and EDFM in any flow scenario, has not yet been integrated into these simulators. In this paper, we introduce a pioneering development of a novel numerical simulation approach specifically tailored for generic pEDFM, designed to enhance gas injection energy in shale gas-condensate reservoirs. This method is the first of its kind to seamlessly integrate pEDFM with a widely used commercial simulator, Computer Modeling Group. By doing so, we ensure not only the practical applicability of the generic pEDFM simulation in the field but also address the challenges associated with developing additional high-performance nonlinear solvers. Three numerical examples demonstrate the advantages of this novel method: compared to DFM, it does not require the generation of grids that match the morphology of the fracture network, thereby reducing computational costs and convergence difficulties; compared to EDFM, it can simulate with much higher accuracy the impact of high- and low-conductivity fractures on compositional flow; and compared to local grid refinement, it can handle more complex fracture patterns. Theoretically, this method is the optimal numerical simulation tool in terms of comprehensive computational performance for research on gas injection energy supplementation in fractured gas-condensate reservoirs. [ABSTRACT FROM AUTHOR]

Foam can effectively improve reservoir heterogeneity, increase gas–liquid flow rate, reduce viscous fingering, and help to improve sweep efficiency. This paper mainly studies the characteristics and performance of microbial foam production, and proposes an enhanced oil recovery method for profile control by in situ microbial foam production. By optimizing the carbon and nitrogen sources of the medium, Pseudomonas aeruginosa PAO1 produced single and double rhamnolipids and biogas composed of N2, CO2, and CH4, and it could also produce foam in high salt, weak acid, and weak alkali environments. Gas injection experiments were carried out using self-produced biogas, the foaming effect is good in the range of gas–liquid ratio 1:1–3:1 and gas injection speed 20–40 ml/min, which was 71.43%–91.25% more than the foam volume produced by CO2 injection, and the foam production was positively correlated with the protein concentration of the foam. In the early stage of incubation, the foam was 20–100 μm in diameter, with high protein concentration and strong foam stability, which slowed down the drainage, polymerization, and disproportionation of the liquid film of the foam system. The foam performance test results show that the foam half-lifetime is long, up to 109 min. Foam culture medium has good viscosity reduction effect, emulsifying properties and less corrosive. The displacement experiment shows that the foam generated in situ by PAO1 in the core has good stability, reproducibility, and profile control performance, which can reduce the permeability of the core to half of the initial permeability and improve the reservoir heterogeneity. Therefore, microbial in situ foam production can be an effective method to enhance oil recovery in heterogeneous reservoirs, which is low cost, low pollution, and simple operation. [ABSTRACT FROM AUTHOR]

Oscillation characteristics in a cavity are investigated under real experimental conditions through unsteady numerical simulations of the time-evolving oscillatory damping of a high-Mach-number freestream over a two-dimensional forward-facing cavity. The post-disturbance flow field is taken as the initial condition. Temporal variations in the flow field and wall resistance coefficient are obtained. The forward-facing cavity experiences underdamped oscillatory behavior when subjected to disturbances. The convergence of the oscillations is influenced by the cavity volume, with significant reductions in cavity damping observed when stagnation regions develop within the cavity. During the initial phase of disturbance, each oscillation cycle consists of gas injection and jet phases. In the former, external gas stagnates within the cavity, resulting in a gradual increase in internal density and pressure. High-temperature regions extend from the external flow into the cavity, and bow shocks approach the cavity wall, adversely affecting aerodynamic drag reduction and thermal protection for aircrafts. In the jet phase, the flow field structure resembles the opposing jet. As the gas is expelled, the internal cavity pressure decreases, forming a cold jet that envelops the cavity's surface. The temperature within the boundary layer on the surface decreases, and bow shocks are pushed away from the wall, resulting in thermal-protection and drag-reduction effects. Transitions between phases induce instability in the internal flow states within the cavity. During the transition from the gas injection phase to the jet phase, the wall drag coefficient reaches its peak value; the reverse transition results in the lowest wall drag coefficient. [ABSTRACT FROM AUTHOR]

Effects of secondary gas injection on flame shape and combustion stability of a premixed swirl methane/air flame were investigated experimentally. Without secondary gas injection, an attached M-shaped flame was observed with pressure oscillations up to a sound pressure level of 68 dB. The flame exhibited significant oscillations due to flame–vortex interactions induced by velocity fluctuations. The secondary methane or air was separately injected into the outer recirculation zone to suppress the flame oscillations at a volume flow rate of 0.5% of the primary flow rates. For lower primary air flow rates ( Q air ≤ 60 L/min), both secondary methane and air injections were able to suppress the thermoacoustic instability and performed the sound pressure level reduction of 45 dB. Meanwhile, the flame transformed from an attached unstable M-shaped flame to a detached stable V-shaped flame. The secondary methane or air injection served to stabilize the flame and anchor its spatial heat release distribution by limiting the variation of flame shape in the outer recirculation zone, suppressing thermoacoustic oscillation. For higher primary air flow rates ( Q air = 80 L/min), the secondary methane injection could reduce sound pressure levels to noise levels, while secondary air injection could not. The velocity disturbances and heat release fluctuations introduced by secondary methane injection could lead to a transformation in flame shape and achieve the suppression of thermoacoustic oscillation. However, the velocity disturbances induced by secondary air injection were insufficient to stabilize the flame. [ABSTRACT FROM AUTHOR]

Atomic layer etching (ALE) schemes are often deemed economically unviable due to their slow pace and are not suited for every material/hard-mask combination. Conversely, plasma etching presents pattern profile challenges because of its inability to independently control ion and neutral flux. In this work, we introduce a new cyclic transient-based process, called transient-assisted plasma etching (TAPE). A cycle of TAPE is a short exposure step to a sustained flow of reactant before the reactant gas injection is stopped in the second step, resulting in a plasma transient. As the plasma ignites and a substantial amount of etchant remains, a chemically driven etching process occurs, akin to conventional etching. Later in the transient, the modified surface is exposed to a reduced etchant quantity and a sustained ion bombardment, in a similar way to ALE. The cointegration of conventional etching and atomic layer etching allows interesting compromises between etch control and processing time. Going for a transient plasma allows to provide the time and conditions needed for the necessary plasma-surface interactions to occur in one step. In this perspective, the mechanisms behind etch rate, profile correction, and conservation of surface composition using amorphous carbon, as a benchmark, are discussed. [ABSTRACT FROM AUTHOR]

In the initial stage of coal seam water injection, due to the high density and low permeability of coal bodies, an obvious startup pressure gradient is observed in relation to water seepage; this phenomenon leads to low-velocity nonlinear seepage. In this paper, we study the nonlinear seepage law and the main influencing parameters of the water injection process. First, based on the startup pressure gradient, the nonlinear seepage equation, and the fractal theory, we formulated a nonlinear seepage model of coal seam water injection that considered the fractal characteristics of a complex coal structure. Subsequently, we carried out coal seam water injection and gas radial seepage experiments under a high overburden pressure, obtaining the startup pressure gradient according to the seepage characteristics and the changes of dynamic parameters. Then, the dynamic parameters of water injection, the structural parameters of the coal samples, the physical parameters, and the fractal dimension were substituted into the theoretical model to obtain the theoretically calculated value. Finally, through comparative analysis of theoretical and experimental startup pressure gradient calculation results, it is found that with the increase in the overburden pressure, the permeability of coal and the connectivity effect are reduced, while the fracture tortuosity and the startup pressure gradient increase. Moreover, coal seam permeability does not seem to be the single decisive factor for the nonlinear startup pressure gradient. [ABSTRACT FROM AUTHOR]

The present study aims to reveal two-phase flow characteristics as gas is injected into co-flowing water. A computational fluid dynamics work was conducted using the volume of fluid model and the delayed detached eddy simulation. The numerical scheme was validated through experimental results. Effects of the upstream water velocity and the gas injection rate on flow patterns were investigated. Characteristics of gas cavities were compared under different operating conditions. In both experimental and numerical results, unique patterns of gas cavities are obtained. A large cavity is attached to the nozzle outlet, and simultaneously, bubbles are shed from the cavity front. With increasing gas injection rate, the attached cavity is pinched off as it extends in a streamwise direction. As the velocity of water increases, scattered pinch-off frequencies are evidenced and cavity instability is enhanced. Liquid wake downstream of the nozzle contributes significantly to the collapse of the gas cavity. A long and stable gas cavity is produced at high upstream water velocities and gas injection rates. [ABSTRACT FROM AUTHOR]

Pulsed electrical discharges in a gas–liquid mixture deposit energy into both phases. Here, we propose a model to simulate breakdown in multiphase based on experimental data. Furthermore, we estimated breakdown voltage in each phase and then estimated energy deposition in each phase. Discharge in pure liquid showed a highly stochastic nature, having a wide breakdown voltage distribution, while the mean value closely follows a one term power law as a function of gap spacing. When there is external gas injection to the gap, breakdown voltage increased significantly due to charge dissipation on bubble surface. This effect was simulated to predict breakdown voltage in liquid with gas injection at different rates. A multiphase system model was developed to simulate breakdown in the gas–liquid phase. The model is a superposition of power law and Meek criteria physical models for the liquid and gas phases, respectively, with empirically derived coefficients. Energy deposition into each phase was estimated by this model. The gap spacing is the primary factor determining breakdown voltage and energy distribution. In studied conditions, we were able to predict the breakdown voltage and estimate energy deposition into different phases. When the gap and flow rate vary between 2 and 10 mm and flow rate 0–1 LPM, 50%–93% of electrical energy is deposited into the liquid. This model allows for predicting breakdown voltage in a multiphase. Furthermore, it allows for control of the energy distribution among the phases in a multiphase pulsed discharge system. [ABSTRACT FROM AUTHOR]

Microseismicity in subsurface geologic environments, such as sandstone gas reservoirs, is expected in the presence of liquid or gas injection. Although difficult to predict, the potential for microseismic events is important to field-scale projects, such as geologic storage of CO2, whereby the gas is injected into natural sandstone formations. We conjecture that a primary factor causing microseismicity is the existence of metastable states in a granular porous medium and provide experimental evidence for its validity. External perturbation triggers abrupt relaxation events which, with a certain probability, can grow into macroscopic microseismic events. Here, the triggering perturbation is produced by cooling to a cryogenic temperature. As the "sensor" for the abrupt relaxation events, we use thin Al films deposited on the sandstone surface. We show that as the temperature is varied, the films' resistance exhibits sharp jumps, which we attribute to mechanical restructuring or microfractures in the fabric of the sandstone. We checked the superconducting characteristics of the Al thin films on the sandstone and found microwave-induced Shapiro steps on the voltage–current diagrams. Such quantized steps provide indications that the film is made of a network of nanobridges, which makes it even more sensitive to abrupt relaxation events occurring in the substrate, i.e., in the underlying sandstone. [ABSTRACT FROM AUTHOR]

For fault-controlled fractured-vuggy reservoirs, the development characteristics of bottom water flooding and water and gas injection flooding under multi-well conditions must be clarified due to the structural complexity. To address this issue, we designed and manufactured fault-controlled physical experimental models based on the geological model of Tarim Oilfield and conducted flooding experiments. The results demonstrate significant variations in bottom water flooding characteristics due to differences in flow capacity within fractures, cavity area in caves, and filled area in caves under different filling modes. Different bottom water rates exhibit varying abilities to overcome gravity and breakthrough capillary resistance, significantly impacting the bottom water flooding characteristics. During the bottom water flooding period, the positioning of production wells primarily affects the macroscopic sweep range, while the filling modes significantly influence the distribution of remaining oil within individual caves. Throughout the three periods of multi-well water and gas injection, the early water injection stage mainly focuses on mobilizing "insufficiently controlled remaining oil" and some "attic remaining oil," and the middle gas injection stage primarily targets the attic remaining oil. Finally, the late water injection stage aims to lift the oil–gas–water interface and improve oil displacement efficiency. Furthermore, different water and gas flooding directions affect displacement resistance in each channel and the longitudinal sweep range. This paper identifies the direction for the life cycle production of fault-controlled fractured-vuggy reservoirs and presents a mechanistic explanation. [ABSTRACT FROM AUTHOR]

The formation of the plasma current spike at the end of the thermal quench (TQ) phase is studied systematically, which is found to strongly correlate with the onset of the 1/1 kink-tearing reconnection only in the simulation results presented here. The magnetohydrodynamic activity on the q = 1 surface plays a critical role in the spike formation and the disruption process. In particular, when the safety factor in the magnetic axis q0 exceeds 1, the plasma major disruption transits into successive minor disruptions, and the start of the TQ phase is delayed. [ABSTRACT FROM AUTHOR]

The flux of CO2 diffusing inside a new type of bioreactors has been measured experimentally. This geoinspired bioreactor consists of a partially filled cylinder rotating around its axis tilted vertically, thus mimicking the precession motion of the Earth. The height of fluid is chosen equal to two radii in order for the first Kelvin mode to be resonant. The CO2 diffuses through a membrane located at the bottom of the liquid. The partial pressure of CO2 above the free surface is measured as a function of time. This temporal evolution is modeled by the presence of diffusive layers with no advection at the top and the bottom of the liquid. This basic model leads to an experimental value for the flux of CO2 at the membrane, which is found to be proportional to the inverse square root of the Ekman number. This is in agreement with the presence of Ekman layers of thickness proportional to the square root of the Ekman number. At a given Ekman number, the flux weakly depends on the tilt angle α with a scaling as α 1 / 4 . [ABSTRACT FROM AUTHOR]

Azimuthal magnetic field measurements obtained during the implosion phase of an oxygen gas-puff Z-pinch on a 500 kA peak current and 180 ns rise time linear transformer driver are presented. While a fraction of the driver current was measured within the imploding plasma, key initial conditions were found to significantly impact the delivery of current to the plasma load. The electrode geometry was modified to assist the initial dielectric breakdown and resulted in improved shot reproducibility. Optimization of the gas injection plenum pressure and timing resulted in an increase in the current coupling parameter, defined as the ratio of the measured value of B θ to the expected value, from 50% to 75%. The degree of radial expansion of the gas puff in the load region, which is suspected to lead to the observed current loss during the implosion, was reduced by shortening the valve opening duration. Additionally, a pre-embedded axial magnetic field of up to 0.2 T was found to have no significant impact on the plasma-current coupling of the oxygen implosions. [ABSTRACT FROM AUTHOR]

A three-dimensional model was developed to investigate the effects of gas nozzle configuration in an industrial gas-stirred ladle on flow pattern, mixing time, heat transfer, inclusion removal, and shear stress on the wall. Population balance model coupled with computational fluid dynamics was chosen to evaluate the inclusion removal. The properties of phases and the size distribution of inclusion were in agreement with literature data. Gas nozzle locations were investigated in terms of radius and angle. It was found that an increase in angle and decrease in radius of gas nozzle location decreased shear stress on the wall. Also, as gas nozzle locations got closer to each other, bubble plumes overlapped, and turbulent kinetics was affected. This in turn affected temperature, mixing time, and inclusion removal. Therefore, by changing angle and radius, these parameters did not have similar trends. From the performed investigations, it was found that the best gas injection location was angle of 140° and radius of 0.65R. Shear stress, mixing time and inclusion removal at ladle with the plug radius of 0.65R were improved by 38.7%, 1.3%, and 0.87%, respectively. In addition, at ladle with the plug angle of 140°, shear stress, mixing time, and inclusion removal were increased by 6%, −6.57%, and 8%, respectively. By choosing this gas injection location, ladle performance was optimum in all parameters. [ABSTRACT FROM AUTHOR]

The characterization of immiscible displacement processes at the pore scale is crucial in order to understand macroscopic behaviors of fluids for efficient use of multiphase transport in various applications. In this study, the impact of porous material wetting properties on gas invasion behavior at various gas injection rates was investigated for thin hydrophilic porous media. An experimentally validated two-phase computational fluid dynamics model was employed to simulate the dynamic fluid–fluid displacement process of oxygen gas injection into liquid water saturated thin porous media. A phase diagram was developed through a parametric characterization of the thin porous media in terms of the material hydrophobicity and gas flow rates. In addition to calculating the saturation of the invading gas, gas pressure variations were calculated and used to identify the locations of phase diagram boundaries. Non-wetting phase streamlines resolved at the microscale were visualized and presented as a novel indicator for identifying displacement regimes and phase diagram boundaries. It was observed that the crossover from the capillary fingering regime to the stable displacement regime occurred between contact angles of 60° and 80°. By increasing the gas injection rate, due to viscous instabilities, flow patterns transitioned from the capillary fingering and stable displacement regimes to viscous fingering regime. [ABSTRACT FROM AUTHOR]

The phenomenon of a bubble bursting to generate droplets exists in industrial and environmental systems and has a subtle impact on our daily lives. A bubble generated by gas injection or heating rises to the free surface and undergoes floating, drainage, and eventually bursting processes to produce film and jet droplets. The interrelated processes make it difficult to understand the characteristics of a bubble burst. Thus, a summary of the individual stages of a single bubble from generation to burst is necessary. First, we describe the calculation method and simple expressions for the shape of a bubble floating on a free surface. Next, we discuss the bubble drainage model and its influencing factors as this directly determines the time evolution of the film thickness. As an essential factor that affects the film thickness, the bubble drainage time is defined as the bubble lifetime. We compare the bubble lifetime distributions in the published literature and explore the associated influencing factors. Then, we investigate the bubble bursting dynamics and focus on the bubble film opening process once a hole appears on its surface. As a legacy of bubble burst, we explore the production process, size, and number of film and jet droplets. Finally, we discuss the enrichment phenomenon and the enrichment factors of film and jet droplets when releasing particles entrained by droplets. This review considers a series of processes for bubble burst to generate droplets and concentrates on the mechanism and experimental correlations with a summary and future prospects. [ABSTRACT FROM AUTHOR]

In this study, the multifaceted asymmetric radiation from the edge (MARFE) was observed in high-density discharges or during impurity gas injection on the EAST tokamak. The MARFE onset indicated by spectral and radiation signals can also be detected by the POlarimeter-INTerferometer (POINT) diagnostic, which measures the horizontal line-integrated density and the Faraday rotation. The fluctuation amplitude of the density signal resulting from the MARFE oscillation increases with the edge safety factor, which is consistent with the thermal instability theory. By combining density and the Faraday rotation, the local current shrinkage in the MARFE region is observed during the MARFE movement. The density and the current profile calculated by the POINT become more peak during the MARFE, which may lead to a strong magnetohydrodynamic instability that can result in disruption. [ABSTRACT FROM AUTHOR]

We present the design and operation of a suite of Gas Puff Imaging (GPI) diagnostic systems installed on the Tokamak à Configuration Variable (TCV) for the study of turbulence in the plasma edge and Scrape-Off-Layer (SOL). These systems provide the unique ability to simultaneously collect poloidal 2D images of plasma dynamics at the outboard midplane, around the X-point, in both the High-Field Side (HFS) and Low-Field Side (LFS) SOL, and in the divertor region. We describe and characterize an innovative control system for deuterium and helium gas injection, which is becoming the default standard for the other gas injections at TCV. Extensive pre-design studies and the different detection systems are presented, including an array of avalanche photodiodes and a high-speed CMOS camera. First results with spatial and time resolutions of up to ≈ 2 mm and 0.5 µs, respectively, are described, and future upgrades of the GPI diagnostics for TCV are discussed. [ABSTRACT FROM AUTHOR]

Real-time bubble behavior characterization is critical in the chemical industry, especially for leakage in sodium–water reactions. In this study, the injection of gas into sodium flows was conducted to evaluate bubble characterization methods. Simulation research was performed to dynamically characterize bubble generation, growth and bursting in flowing sodium, and experimental research was conducted to explore the time-frequency and time domain statistical characteristics of bubble signals. After gas injection, significant low-amplitude signals were observed in the time domain, the power spectral density fluctuated in the 0–20 kHz band; its spectral components were more abundant above 8 kHz, and the short-time Fourier transform of the energy spectrum exhibited a nonlinear intermittent distribution in the 8–20 kHz band. Based on these differences, the bubble signal was effectively detected when the gas injection rate was 0.11 m3/h with a signal-to-noise ratio less than 0.5 dB. Thus, this study complemented the present techniques and knowledge in the field of chemical engineering. [ABSTRACT FROM AUTHOR]

We have used the Maxwell–Stefan diffusion theory to model the mass transfer between tertiary-injected gas and residual oil blocked by water, in order to predict the time required for the rupture of the water barrier due to oil swelling. We have also designed and conducted a set of visualization micromodel experiments on various pure and multicomponent oil–gas systems to measure the water rupture time in tertiary gas injection processes. The experimental results show that the initial pressure and dimensions of the system, the oil and gas composition, and the gas solubility in water control the oil swelling process. The experimentally measured rupture times are then employed to evaluate the reliability of the model and to compare its accuracy with that of a similar one using classical Fick's law. Our modeling results show that both models are able to estimate the water rupture time for pure systems with an acceptable precision. As for multicomponent mixtures, however, only the Maxwell–Stefan theory is capable of modeling the molecular diffusion process correctly and yields values close to reality, while the use of Fick's law would lead to erroneous results. Deficiency of the latter model becomes more acute when the diffusion direction in reality is contrary to what the model indicates, which leads to failure in calculating any value for rupture time at all for these cases. [ABSTRACT FROM AUTHOR]

Hydrodynamics and residence time distribution (RTD) of fluid elements are key parameters to characterize the performance of stirred vessel. They are governed by geometric and operating parameters of the stirred vessel (SV). In the present work, the performance of the stirred vessel is studied using computational fluid dynamics (CFD) with realizable k−ε turbulence model. The multiple reference frame and sliding mesh approach are used for impeller motion. The solid–liquid flow and associated solid suspension characteristics are predicted using the two-fluid model (Euler–Granular). The performance of the stirred vessel is characterized by analyzing predicted velocity magnitude, solid concentration (suspension quality), and solid sedimentation. This is compared with the stirred vessel with draft tube baffle configuration (three inner baffles and six outer baffles). The recirculatory flow in draft tube SV helps to achieve uniform suspension and less sedimentation. Further, CFD simulations are carried out in Lagrangian way to analyze chaotic mixing among fluid elements. This is qualitatively analyzed using Poincaré map and quantitatively evaluated using Shannon entropy. The extent of chaotic mixing in draft tube SV is found to be high. The performance of the stirred vessel is further investigated through stimulus–response tracer techniques (RTD) to detect design flaws such as bypass and dead zones. This is analyzed for a wide range of operating parameters and identified optimum conditions (flow rate, impeller speed) for the operation of SV. The four different outlet pipe locations are chosen in SV. The bypass and dead volume are analyzed accordingly, and an optimum outlet pipe location is found. To reduce the extent of non-ideal parameters, three different gas source locations are considered and gases are dispersed in the form of bubbles. The gas dispersion at optimum gas injection point is found to reduce non-ideal parameters and improve the design of stirred vessel. [ABSTRACT FROM AUTHOR]

Ammonia is an alternative fuel that has potential in much industrial equipment such as internal combustion engines, gas turbines, and boilers. In the present study, the influence of flue gas on the injection process of ammonia fuel was analyzed for the first time, and the influences of ammonia/methane fuel ratio and equivalence ratio on the diffusion process were considered. A Schlieren system was used to characterize the characteristics of ammonia jet, including tip penetration and jet angle. Meanwhile, the NO emissions during this progress were calculated based on the GRI 3.0 combustion mechanism. The results showed that the penetration distance was affected by both the diffusion effect and the chemical effect. The time evolution of penetration has three stages. The second stage of penetration in the flue gas environment develops faster with the decrease in the equivalence ratio. The increase in jet angle is accelerated by the flue gas environment and a decrease in equivalence ratio. Furthermore, the theoretical results showed that the emission process of NO is mainly affected by the fuel ratio and equivalence ratio. When the equivalence ratio increased from 0.8 to 1.2, NO emissions decreased by 85.7%. The distribution of NO along the axis is also affected by the fuel ratio. When the volume ratio of NH3 to CH4 decreases from 1 to 0.5, the peak value of NO concentration decreases by 29.4%. [ABSTRACT FROM AUTHOR]

A convergent gas feeding method is proposed to alleviate neutral gas depletion near the central plasma region in typical electrodeless radio-frequency (RF)/helicon plasma thrusters. To achieve further performance improvement, the SuperSonic Gas Puffing (SSGP) system is one of the methods that is expected to overcome the above-mentioned depletion and the density limit. This study discovered that the spatiotemporal profiles of the neutral pressure and the estimated gas diffusion angle vary depending on the SSGP gas feeding condition, i.e., the nozzle size, filling pressure, and the valve opening time. Convergent gas feeding is successfully conducted using the SSGP method in a vacuum. As a preliminary study, high-density plasma is also obtained in the vicinity of the gas injection region using the developed SSGP system. The effects of the gas feeding position and an external divergent magnetic field on the plasma density are investigated. A suitable gas feeding position/region exists for plasma generation using the RF/helicon plasma thruster. [ABSTRACT FROM AUTHOR]

Aerodynamic drag reduction is crucial for the development of high-speed trains. This study considers the principle of supercavitation torpedo drag reduction and conducts wind tunnel tests and improved delayed detached eddy simulation numerical simulations to develop a drag reduction technique using low-density gas injection on the surface of a high-speed train. Models for jetting gases with different densities on the surface of the high-speed train were employed, and the aerodynamic drag, frictional resistance, pressure resistance, and flow field structure were compared and analyzed. The results demonstrated that jetting of low-density gas reduced the drag of the train, whereas air and high-density gas increased the drag. The jetting gas reduced the frictional resistance of the train to a certain extent and low-density gas injection significantly reduced the frictional resistance. However, the pressure resistance coefficient increased with an increase in the density of the jetting gas, resulting in increased drag. The density of the gas medium in the boundary layer significantly decreased when low-density gas was jetted and the effect of reducing the friction resistance was superior. The pressure resistance between the front and rear of the jet port increased with an increase in the gas density, thereby increasing the drag on the train. [ABSTRACT FROM AUTHOR]

Carbon capture, utilization, and storage have been an effective way to deal with global climate issues. Injecting CO2 into depleted oil reservoirs can reach the dual goal of carbon storage and enhanced oil recovery. To optimize the gas injection strategy, it is necessary to understand the underlying mechanisms of three-phase fluid flow of oil, water, and gas. In this study, a lattice Boltzmann color gradient model is used to investigate the pore-scale three-phase displacement process in porous media. Gas is injected into the porous domain initially occupied by water and oil. Typical microscopic behaviors, including coalescence and split-up, pinch-off, double and multiple displacement, as well as parallel flow, are identified and discussed. Effects of water content (ϕ), capillary number (Ca), wettability and viscosity ratio (M) on the flow pattern, and oil recovery rate are explored. The oil ganglia inhibit the development of gas fingers, causing stronger viscous fingering characteristics with increasing ϕ. The fingering pattern is located in the crossover zone for the Ca from 5 × 10−5 to 5 × 10−4. As ϕ increases, the oil recovery rate reduces. The oil ganglia tend to occupy small pores as oil wettability enhanced, making it more difficult to be drained out. The reduction of oil viscosity is beneficial to improve connectivity, thereby effectively enhancing the oil recovery. Finally, the CO2 storage rate is also evaluated. It is found that the storage rate is very sensitive to the initial oil–water distributions. In general, the storage rate increases as ϕ decreases, Ca increases, and oil wettability enhances. [ABSTRACT FROM AUTHOR]

Advanced materials and new lightweighting technologies are essential for boosting the fuel economy of modern automobiles while maintaining performance and safety. A novel approach called subcritical gas-laden pellet injection molding foaming technology (SIFT) was performed to produce foamed polyamide/glass fiber (PA/GF) composite. Gas-laden pellets loaded with nitrogen (N2) were produced by introducing sub-critical N2 into PA/GF composite during compounding using a twin-screw extruder equipped with a simple gas injection unit. Compared to the commercial microcellular injection molding (MIM) technologies, gas-laden pellets enable the production of foamed parts with a standard injection molding machine, which is more cost-effective and easier to implement. To the best of our knowledge, this is the first attempt that the SIFT technology is being used for the PA/GF composites for making foamed parts. The tensile strength, fiber orientation, cell morphology, and densities of foamed PA/GF parts were investigated, and the shelf life of N2-laden PA/GF pellets was examined. Results showed that the N2-laden pellets still possessed good foaming ability after one week of storage under ambient atmospheric conditions. One week is a noticeable improvement compared to those N2-laden neat polymer pellets without glass fibers. With this approach, the weight reduction of foamed PA/GF parts was able to reach 12.0 wt. %. Additionally, a nondestructive analysis of the fiber orientation using micro-computed tomography suggested that the MIM and SIFT samples exhibited a less degree of fiber orientation along the flow direction when compared to the solid samples and that the tensile strength of both technologies was very close at a similar weight reduction. Cell size increased and cell density decreased as the shelf life increased. These findings showed that this processing method could act as an alternative to current commercial foam injection molding technology for producing lightweight parts with greater design freedom. [ABSTRACT FROM AUTHOR]

We describe an automated gas sampling and injection unit for a gas chromatograph (GC). It has specially been designed for low concentrations of products formed in catalytic in situ and operando experiments when slow reactions on single crystal models are investigated. The unit makes use of a buffer volume that is filled with gas samples from the reactor at a reduced pressure. The gas samples are then compressed by He to the injection pressure of 1000 mbar and pushed into two sample loops of the GC, without major intermixing with He. With an additional cryo trap at one of the GC column heads, the design aims at concentrating the gas samples and focusing the peaks. The performance is characterized by experiments on the Fischer–Tropsch synthesis, using H2/CO mixtures (syngas) at 200 and 950 mbar and a Co(0001) single crystal sample as model catalyst. Chromatograms recorded during the reaction display sharp, well separated peaks of saturated and unsaturated C1 to C4 hydrocarbons formed by the reaction, whereas the syngas matrix only gives moderate signals that can be well separated from the product peaks. Detection and quantification limits of 0.4 and 1.3 ppb, respectively, have been achieved and turnover numbers as low as 10−5 s−1 could be measured. The system can be combined with all known analysis techniques used in in situ and operando experiments. [ABSTRACT FROM AUTHOR]

Three-phase displacement process in a porous media is significantly influenced by wettability of the solid surfaces. It remains a research challenge to model and simulate three-phase flows with moving contact lines, especially on arbitrary complex three-dimensional surfaces. We propose a color-gradient lattice Boltzmann model to simulate immiscible three-phase flows with contact-line dynamics. Unlike the previous models in dealing with wettability through assigning virtual mass fractions to the solid surfaces, the present model realizes the prescribed contact angles by correcting the orientation of the color-gradient parameter at the solid surfaces. We first validate this model against analytical solutions by simulating several typical cases, including a Janus droplet deposited on a flat surface and on a spherical surface, and the spontaneous imbibition of ternary fluids in a cylindrical tube. We then use it to study the displacement of residual oil during tertiary gas injection process. To mimic this process, gas is injected into a simple pore-throat connecting structure after water flooding. Results show that in displacement process, an oil spreading layer forms, which changes the oil flow state from adhering to the bottom wall to spreading over the entire interface between gas and water. Therefore, residual oil can be easily recovered in the form of gas-to-oil-to-water double displacement chain, leading to a high oil recovery regardless of the wetting properties of the solid surface. In the cases without the presence of oil spreading layer, increasing capillary number favors the oil recovery under certain wetting conditions only. [ABSTRACT FROM AUTHOR]

A cylindrical target with a high degree of closure was exposed to ITER divertor-relevant plasmas with typical electron temperatures of 2 eV, electron densities of 5 ⋅ 10 20 m − 3 , and heat fluxes up to 20 MWm − 2 in the linear device Magnum-PSI. By terminating the plasma in an unpumped closed volume, neutral pressures were enhanced from about 0.5 to 20 Pa without any increase in the neutral flux returning to the plasma. Such pressures were sustained largely by the pressure exerted by the incoming plasma. By means of hydrogen gas injection, internal neutral pressures of up to 40 Pa were reached during plasma exposure. We find that at these high neutral pressures, a < 1 eV recombination front forms and expands from the back of the cylinder, so that downstream density drops dramatically. Furthermore, in these scenarios, heat deposition to the back plate vanishes and is redirected to the upstream part of the cylinder and to hot neutrals, which can carry 50% of the plasma input power. A power balance analysis reveals that even without additional gas puffing, only about 10% of the incoming heat load reaches the back plate for the 20 MWm − 2 plasma. These results demonstrate the important role of closed target configurations and local gas puffing in mitigating plasma heat loads and indicate that the gained experience should be taken into account in next-generation divertor designs. [ABSTRACT FROM AUTHOR]