Gas Expansion Research Articles

Thermal dynamics of leader decay and reactivation in long air gap discharges

In this study, we present a comprehensive investigation of positive leader discharges, with the aim of enhancing our understanding of leader decay and reactivation. Our approach involved a detailed experimental and computational analysis of the phenomena. Specifically, we employed a time-resolved quantitative Schlieren platform, which provided us with high spatial resolution (60.0 μm pixel−1) and short exposure times (0.37 μs frame−1), allowing us to capture the 2D spatial–temporal evolution of gas temperature in positive leaders with a gap length of up to three meters. In addition, we employed a detailed thermal-hydrodynamic model coupled with a comprehensive kinetic scheme, consisting of 28 chemical species and 125 chemical reactions. Our simulations showed good agreement with the measured mean gas temperature and expansion rate of thermal radius. We conducted experiments under the same applied conditions to obtain both stable and decaying leaders. Our results show that once a positive leader starts to decay, the temperature drops below 3000 K. At the same time, both the electric field and conductivity decrease significantly compared to a stable leader. In addition, before the temperature drops below 2000 K and transforms into an aborted leader, a decaying leader might be reactivated.

Investigation of a sole gas expander for gas pressure regulation and energy recovery

To recover pressure energy effectively during the gas pressure regulation, innovatively, this work proposed a sole expander for gas pressure regulation and energy recovery: By detecting the outlet gas pressure, the PID controller to control the speed of the expander through the magnetic brake, which adjusts the gas flow, and the outlet gas pressure of the expander reaches stable in this way. By establishing an experimental platform, the pressure regulation and energy recovery performance was investigated in detail. Results showed that three PID parameters P, I and D exerted different influence on pressure regulation, and an optimal pressure regulation accuracy of 1.0% was observed at the optimal PID parameters (P = 15%, I = 50 and D = 2). The gas flow has a certain influence on the pressure regulation while the target pressure has no obvious impact on pressure regulation. The pressure regulation accuracy at maximum flow and minimum flow is limited to the allowable speed and inter leakage of expander. The output power was influenced greatly by gas flow, and a maximum output power 145 W was obtained. The method proposed in this work is proved to be feasible and reliable and has good prospect in gas pressure regulation and energy recovery area.

Methane hydrate exploitation characteristics and thermodynamic non-equilibrium mechanisms by long depressurization method

Methane hydrate as a clean energy source has attracted worldwide attention. Yet, thermodynamic evolution of methane hydrate-bearing deposits during long depressurization are still unclear. In this study, five methane yields (1.17, 0.77, 0.41, 0.21 and 0.13 Ls/min) for exploitation were conducted to simulate long depressurization of thousands of minutes. The rates of both depressurization and hydrate dissociation are linearly enhanced by increasing methane yield. Icing is always observed when the pressure reaches approximately 2.4 MPa unless the hydrate dissociation already finished. The accelerating effect of icing on hydrate dissociation can be strengthened by high methane yields. Thermodynamic responses at different exploitation stages are different because of the varied combinations of some non-equilibrium processes including gas expansion, hydrate dissociation, icing and melting as well as heat transfer. In this study, there are four thermodynamic non-equilibrium phenomena, respectively are gas expansion production, non-isothermal heat transfer, hydrate stationary dissociation and ice isothermal melting. The thermodynamic controlling mechanism and influencing factors of different exploitation stages are analyzed qualitatively or quantitatively, which reveals the temperature response of methane hydrate exploitation during long depressurization process. These results are helpful for understanding complex coupling mechanism of phase change and heat and mass transfer in methane hydrate exploitation.

Expansile gas kinetics for pneumatic retinopexy.

To study the behaviour of expansile intravitreal gases and air used in treating rhegmatogenous retinal detachment. A validated mathematical model of gas expansion and absorption in human eyes was used to simulate the effect of varying volumes of pure air, SF6, C2F6 and C3F8 injected into the vitreous cavity. Variation in axial length was accounted for by using three different vitreous cavity volumes to represent hypermetropic, emmetropic and myopic eyes. The time course of varying volumes of pure air and fluorinated gases injected into the vitreous cavity were tabulated, with calculated parameters including volume of gas, percentage gas fills and corresponding retinal contact angles at different time points. We produced a comprehensive compilation of expansive gas kinetics aiming to facilitate surgeon selection of the most suitable choice of gas and volume to use, tailored to an individual patient's clinical need.

Altitude and gas expansion in repaired rhegmatogenous retinal detachment.

Altitude and gas expansion in repaired rhegmatogenous retinal detachment.

Surface geochemical anomaly pattern of medium-to-high temperature geothermal systems in South China and its application

The existence of thermal storage will correspondingly increase the temperature of surrounding strata and promote the continuous expansion, volatilization, upward migration, and loss of gas in the strata. As a result, a low-concentration gas field will be formed in the strata above geothermal reservoirs. Geothermal reservoirs could in turn heat formation water and increase the solubility of soluble inorganic salts in the surrounding rocks and the total dissolved solids (TDS) content in the formation water. Since water can strongly wet and permeate strata, the dissolved inorganic salts migrate into upper strata along with water, giving rise to the formation of a high-concentration inorganic salt field in the strata above geothermal reservoirs. A higher geothermal reservoir temperature corresponds to more significant characteristics mentioned above. Therefore, a medium-to-high temperature geothermal system has a surface geochemical anomaly pattern of high inorganic salt concentrations and low gas concentrations (also referred to as the high-salt and low-gas pattern). This pattern is applied to the surface geochemical exploration of the two geothermal fields in Guangdong Province, i.e., the Huangshadong geothermal field in Huizhou City and the Xinzhou geothermal field in Yangjiang City, revealing low-concentration gas fields above both. The application results also show that the exposed thermal spring water in both geological fields has higher concentration of dissolved inorganic salt than the surface water and nearby seawater, forming high-amplitude anomalies on the surface above geothermal reservoirs. These characteristics, as well as the measured temperature at known geothermal wells, verify the validity of the high-salt and low-gas pattern of medium-to-high temperature geothermal systems proposed in this study. Moreover, the high-salt and low-gas pattern proposed predicts three favorable medium-to-high temperature geothermal zones in the surface geochemical exploration of the Shiba Basin near the Huangshadong geothermal field.

Experimental study on solid particle migration and production behaviors during marine natural gas hydrate dissociation by depressurization

Sand production is one of the main obstacles restricting gas extraction efficiency and safety from marine natural gas hydrate (NGH) reservoirs. Particle migration within the NGH reservoir dominates sand production behaviors, while their relationships were rarely reported, severely constrains quantitative evaluation of sand production risks. This paper reports the optical observations of solid particle migration and production from micrometer to mesoscopic scales conditioned to gravel packing during depressurization-induced NGH dissociation for the first time. Theoretical evolutionary modes of sand migration are established based on experimental observations, and its implications on field NGH are comprehensively discussed. Five particle migration regimes of local borehole failure, continuous collapse, wormhole expansion, extensive slow deformation, and pore-wall fluidization are proved to occur during depressurization. The types of particle migration regimes and their transmission modes during depressurization are predominantly determined by initial hydrate saturation. In contrast, the depressurization mainly dominates the transmission rate of the particle migration regimes. Furthermore, both the cumulative mass and the medium grain size of the produced sand decrease linearly with increasing initial methane hydrate (MH) saturation. Discontinuous gas bubble emission, expansion, and explosion during MH dissociation delay sand migration into the wellbore. At the same time, continuous water flow is a requirement for sand production during hydrate dissociation by depressurization. The experiments enlighten us that a constitutive model that can illustrate visible particle migration regimes and their transmission modes is urgently needed to bridge numerical simulation and field applications. Optimizing wellbore layout positions or special reservoir treatment shall be important for mitigating sand production tendency during NGH exploitation.

Modeling the 2022 τ-Herculid Outburst

The τ-Herculids (IAU shower number 61 TAH) is a minor meteor shower associated with comet 73P/Schwassmann–Wachmann 3, a Jupiter-family comet that disintegrated into several fragments in 1995. As a consequence of the nucleus breakup, possible increased meteor rates were predicted for 2022. On May 30–31, observation networks around the world reported two distinct peaks of TAH activity, around solar longitudes 69.°02 and 69.°42. This work examines the encounter conditions of the Earth with meteoroids ejected from 73P during the splitting event and on previous perihelion passages. Numerical simulations suggest that the main peak observed in 2022 was caused by meteoroids ejected from the splitting nucleus with four times the typical cometary gas expansion speed. High-resolution measurements performed with the Canadian Automated Meteor Observatory indicate that these meteoroids are fragile, with estimated bulk densities of 250 kg m−3. In contrast with the main peak, the first TAH activity peak in 2022 is best modeled with trails ejected prior to 1960. We find that ordinary cometary activity could have produced other TAH apparitions observed in the past, including in 1930 and 2017. The extension of our model to future years predicts significant returns of the shower in 2033 and 2049.

Stretch Effects in Large Eddy Simulation of Turbulent Premixed Bunsen Flames

ABSTRACT The stretch effects in large eddy simulation (LES) of a turbulent lean propane-air premixed Bunsen flame in the wrinkled flamelet regime are investigated. A simple approach to model the subgrid-scale flame stretch is proposed. It is based on the analysis which shows that, when the surface-filtered strain rate in a subgrid-scale stretch model is approximated using the volume-filtered velocity field solved for in LES, heat release and associated gas expansion in the filtered flame brush tend to artificially alter the wrinkling of resolved flame fronts. To minimize such artifacts, it is suggested that the volume-filtered strain rate on the unburned side of the filtered flame brush be used to approximate the surface-filtered strain rate and projected through the filtered flame brush. The results show the importance of mitigating the artificial heat release effects when considering the strain effects in LES. The relative importance of the curvature stretch is also investigated in terms of the mean and local effects. For a Bunsen flame with a positive Markstein number, the mean flame curvature effect tends to increase the total burning rate by enhancing the laminar flame speed near the flame tip, while the local flame curvature effect tends to decrease the total burning rate by suppressing the wrinkling of the resolved flames. It is found that the competition between the two makes the overall curvature effects not influence the total burning rate much for the flame investigated here, as compared with the strain effects.

Kinetics of the cross‐reaction of CH3O2 + HO2 radicals measured in the Highly Instrumented Reactor for Atmospheric Chemistry

AbstractThe sensitive Fluorescence Assay by Gas Expansion (FAGE) method has been used to detect methyl peroxy (CH3O2) and hydroperoxyl (HO2) radicals after their conversion by titration with excess NO to methoxy (CH3O) and hydroxyl (OH) radicals, respectively, to study the kinetics of the reaction of CH3O2 + HO2 radicals. The rate coefficient of the reaction was measured in the Highly Instrumented Reactor for Atmospheric Chemistry (HIRAC) at 1000 mbar of synthetic air at T = 268–344 K, selectively detecting both radicals. Using a numerical model to fit both CH3O2 and HO2 radical temporal decays globally at each temperature investigated, rate coefficients for the reaction have been obtained. The room temperature rate coefficient was found to be kCH3O2 +HO2(295 K) = (4.6 ± 0.7) × 10−12 molecule−1 cm3 s−1 (2σ errors) and the temperature dependence of the rate coefficient can be characterized in Arrhenius form by kCH3O2 + HO2(268 K < T < 344 K) = (5.1 ± 2.1) × 10−13 × exp((637 ± 121)/T) cm3 molecule−1 s−1. The rate coefficients obtained here are 14%–16% lower than the literature recommended values with an uncertainty which is reduced significantly compared to previous reports.

Об эффективности легкосбрасываемых конструкций, расположенных в покрытии

The dynamics of the development of an internal explosion is studied considering the action of blast relief panels. The time spent on the exit of the blast relief panel from the opening, as well as the effect of gravity, are considered. The processes are investigated from the moment the blast relief panel leaves the opening and until it is fully opened. A model is formed considering the initial speed of the blast relief panel at the exit from the opening. The model is limited to considering the pressures, at which it is assumed that the degree of expansion of gases during combustion is unchanged, and to determine the rate of gas outflow, the Bernoulli equation for an incompressible liquid is applicable. Dimensionless complexes and parameters characterizing the process under study are established. As a final result, the dependence of the maximum pressure during the opening-up of the opening (the first peak) from the dimensionless complex based on the initial data is proposed. Among them are the characteristics of the blast relief panel, the combustion rate, the geometric shape, and dimensions of the opening. It is concluded that the maximum possible pressure at the first peak does not directly depend on the area of the opening. The rate of pressure relief at the moment of opening-up of the opening is determined by the area of the side space calculated as the product of the perimeter of the opening to the amount of displacement of the blast relief panel. A method is proposed for reducing pressure at the first peak by increasing the number of openings while maintaining the total area for pressure relief, which depends on the bearing capacity of panels. The results obtained allow to establish under what conditions the pressure at the first peak exceeds the pressure at the second one. Thanks to this, it is possible to adjust the explosion resistance of an object by changing the design of a blast relief panel, or by strengthening the load-bearing elements.

Numerical Investigation of Compression and Expansion Process of Twin-Screw Machine Using R-134a

Increasing the efficiency of twin-screw machines is beneficial for gas compression and expansion applications. We used a computation fluid dynamic approach to obtain the flow field and efficiency of a twin-screw machine that used R-134a as the working fluid. The leakage flow and sealing lines were obtained to study their geometrical effects during the compression and expansion process. The effects of the wrap angle (280°, 290°, and 300°) and pressure ratios on the compression efficiency were studied. During the compression process, the volumetric efficiency was more than 70% regardless of the wrap angle. We found that the volumetric efficiency slightly decreased when the wrap angle increased. However, the effect of the wrap angle on the isentropic efficiency was not substantial. An increase in the pressure ratio decreased the mass flow rate and increased the leakage flow. This screw machine can also be operated in an expansion process, and the simulated expansion ratio was 3:1. However, this expansion ratio contributed to an underexpanded condition, which led to a lower volumetric and isentropic efficiencies compared with the original built-in expansion ratio scenario.

Do shale oil and gas production activities impact ambient air quality? A comprehensive study of 12 years of chemical concentrations and well production data from the Barnett Shale region of Texas

Starting around 2008, there was rapid expansion of oil and natural gas (ONG) production into more heavily populated areas within the Dallas-Fort Worth metroplex in the Barnett Shale region of Texas. This colocation raised concerns regarding the effect of ONG activities on chemical levels in the air. In the current study, we examined the potential impacts of ONG activity on the types and concentrations of chemicals in ambient air in the Barnett Shale. Volatile organic compound (VOC) concentrations from 6–12 years (2008–2019) of hourly ambient air monitoring data from 15 monitors (4 monitors had ≥ 10 years of data) were compared to several metrics of ONG activity (number of active wells, natural gas production, condensate production) within a 2-mile radius of each monitor. Monitoring sites were also classified into urban, suburban, and rural areas as a surrogate for nearby vehicular emission sources. Analyses of this huge dataset showed that both peak and mean chemical concentrations of lighter alkane hydrocarbons (e.g., ethane) were most impacted by the number of gas wells. Levels of heavier alkanes (e.g., pentane) were increased by condensate production and at monitors located in areas with greater urbanicity, and therefore higher vehicular emissions. The levels of unsaturated alkynes (e.g., ethylene) were entirely driven by urbanicity and were unaffected by nearby ONG activity. The same pattern was seen with the ratio of iso:n-pentane, which is contrary to the findings of others and suggests an area for future research. Aromatic hydrocarbons were impacted by multiple emissions sources and did not show the same patterns as non-aromatic VOCs. No VOC concentrations were at levels of concern for human health or odor based on comparison to Texas air monitoring comparison values. Overall, ONG activities impact air quality, but this must be evaluated in the context of other emission sources such as automobiles.

On the gas heating effect of helium atmospheric pressure plasma jet

Plasma medicine is an emerging research field which has been driven by the development of plasma sources suitable to generate low temperature plasmas. In many cases, such devices can operate without a gas flow, producing a plasma discharge from the ambient air. However, the most common case is the use of a working gas at a given flow rate to produce a plasma jet. Helium (He) is one of the gases commonly used as the carrier gas to generate cold atmospheric pressure plasma jets (CAPPJs) due mainly to the easiness to ignite a gas discharge with it. However, in this work it was observed that most of the heating of a He CAPPJ can come just from the expansion of the He gas. This was found through measurements of gas temperature (T gas ), using fiber optic temperature (FOT) sensors, and thermal output, using both FOT and infrared imaging with the He flow impinging on a copper (Cu) plate. Such findings were achieved through comparisons of T gas and the temperature on the Cu (T Cu ) plate in the conditions with and without discharge ignition, as well as comparing T gas in the free gas/jet mode with and without discharge ignition. It was verified that the T gas values increased as the distance from the gas outlet was enlarged, especially at low He flow rates, even without discharge ignition. Despite the temperature increase with distance, it is possible to produce plasma jets with temperatures lower than 40 °C at low He flow rates.

Experimental and numerical investigation on water entry fluctuation effect of flared cavity

The water entry of flared cavity is a strong nonlinear process of multi-phase and multi domain coupling. In the process of liquid flowing into or out of flared cavity, there will be an obvious gas expansion and contraction in the cavity, which will not only lead to the bubble wall fluctuation, but also lead to the cyclic fluctuation of flared cavity's motion and load characteristics. In this study, a series of water entry tests of flared cavity were carried out, the fluctuation phenomenon of flared cavity during water entry was found, and their physical mechanism were revealed. Meanwhile, a hydrodynamic model is established to take into account the effect of gas pressure expansion and contraction, and a method of predicting the total pressure of flared cavity is proposed. The results show that: 1) During the water entry of flared cavity, the speed and pressure time history have obvious fluctuations effects, and the larger the water entry speed is, the more obvious the fluctuation effect is. 2) As the air density in the cavity increases, the gas compresses and the pressure in the cavity increases as well; Correspondingly, the air density in the cavity decreases, the gas expands and the pressure in the cavity decreases at the same time. 3) Compared with the surface closed objects, the water entry of flared cavity is affected not only by the hydrostatic pressure and dynamic pressure but also by the air pressure. Based on this rule, a prediction model (PMSP) of flared cavity's total pressure is proposed.

Gas expansion patterns in the reacting submerged gas jet into liquid

The reacting submerged gas jet into a liquid bath is applicable in many industrial processes. The jet is featured with violent gas expansions due to the gas momentum and the liquid evaporation caused by the heat released from the chemical reaction. The gas expansion dictates the gas–liquid interface fluctuation that is closely related to the break-off of the gas phase, gas/liquid reverse flow, and back attack phenomenon. These phenomena are typically hazardous in actual applications. Gas expansion and its underlying mechanisms remain unclear. We experimentally studied the reacting submerged gas jet into a liquid with a HCl/aqueous ammonia system at different liquid temperatures. Results indicate that two expansion patterns exist: the attached expansion pattern and the detached expansion pattern. At the liquid temperature of T = 21 °C, only the attached expansion pattern occurs. At T = 57 °C, both the attached and detached expansion patterns arise. Under the attached expansion pattern, the break-off happens close to the nozzle, and the back attack phenomenon typically occurs. Under the detached expansion pattern, the break-off happens away from the nozzle, and almost no back attack occurs. Subsequently, gas–liquid interface fluctuations at different liquid temperatures were compared. At T = 57 °C, the interface dynamics near the nozzle differs from that away from the nozzle. Finally, the dimensionless number Str Φ=(fd0/u) ΔH/(CpΔT) was proved to have no dependence on the liquid temperature. It is a proper number to describe the dimensionless frequency of the periodic oscillation of the gas-phase length at base frequency.

Numerical Study on the Mechanism of Coal and Gas Outburst in the Coal Seam Thickening Area during Mining

Most coal and gas outbursts occur in the coal thickness variation zone. However, it is difficult to illustrate the mechanism of outbursts in coal thickening areas by physical simulation experiments. In this study, a coupled multi-field model, established by considering the stress–strain field, gas transport field and damage field, was used to investigate the evolution of stress, gas pressure and plastic failure zones under different variation gradients and amplitudes of coal thickness. The simulation results show that the stress peak at the coal thickening transition zone caused by mining is higher than that at the constant thickness coal seam. The stress peak at the coal thickening transition zone decreases from 18.8 MPa to 16.9 MPa with the increase in the transition zone from 0 m to 10 m under the constant coal thickness variation from 3 m to 7 m; while it increases from 16.2 MPa to 19.3 MPa with the increase in the transition zone from 2 m to 10 m under the constant coal thickness variation gradient of 45°. Similarly, the plastic deformation volume of the coal seam between the driving face and the coal thickening interface increases with the increase in the coal thickness variation gradient and amplitude. In addition, the gas pressure in the fracture declines slower in the coal thickness variation zone affected by the higher coal thickness variation gradients or amplitudes. The mechanism for outbursts occurring in the increasing coal thickness area was further discussed, and combined with the simulation results for the energy principle of outbursts. Compared with the constant thickness coal seam, the elastic energy increases from 1.85 MJ to 1.94 MJ, and the free gas expansion energy increases from 24.19 MJ to 50.57 MJ when the coal thickness varies from 3 m to 13 m within a 10 m transition zone. The variation of coal thickness causes higher stress, higher gas pressure and low coal strength, which triggers outbursts more easily. The research could provide the theoretical support to prevent and control outbursts in coal seam thickening areas during mining.

Influence of the pulse polarity on micro-hollow cathode helium plasma jet

Helium plasma jets generated by micro-hollow cathode discharge (MHCD) with the square-wave power source of different polarities are investigated in this work. The effects of positive and negative polarity pulses on the MHCD and plasma jet were compared, and the time-resolved optical emission spectra of excited species ( and O) were studied. The results confirm that the electric field is a key factor for the propagation of the jet during the rising edge of the positive current pulse, while the gas expansion is mainly important for the jet propagation during the current stable phase. The time-resolved spectra show that the generation of specie O in the jet-driven by the electric field is more efficient.

Study on the law of initial gas expansion energy and its feasibility in coal and gas outburst prediction

In order to explore the relationship between IEERG and outburst intensity and verify the feasibility of the former in predicting coal and gas outburst, a series tests with different gases and different gas pressures were conducted on the basis of self-developed coal and gas outburst simulation system and IEERG measuring instrument. The results show that with the increase of gas pressure, the IEERG increases gradually. Under the same gas pressure, the coal has the strongest adsorption capacity for CO2, followed by CH4 and N2. When the IEERG is less than 24.40mJ·g-1, no outburst will occur. When the IEERG is greater than 24.40mJ·g-1, weak outburst will occur. When the IEERG is greater than 34.72mJ·g-1, strong outburst will occur. This shows that the magnitude of IEERG is closely related to the outburst. The larger the IEERG, the greater the possibility of outburst and the greater the intensity of outburst. It is feasible to predict the risk of outburst using IEERG, and it can be quantified.

A Chamber Pressure Prediction Method Based on Strain Measurement of Composite Barrel Recoilless Guns

To predict the chamber pressure of positions corresponding to the strain data of the gun barrel’ outside walls, this study measures the chamber pressure and strain of different positions in a recoilless gun, and proposes a chamber pressure calculation method which is based on strain measurement of cylinder walls using the single-layer thin-walled cylinder theory and the plane strain-elastic stress solution for multi-layer orthotropic cylinders. Experimental results showed that the deformation of the recoilless gun at different positions was caused by varying factors. Specifically, chamber deformation was attributed to the expansion of high-pressure propellant gas, showing a strain curve similar to that of chamber pressure. The deformation of the barrel part between the chamber throat and the muzzle was first caused by band engraving and then by the expansion of high-pressure propellant gas. If the effect of band engraving was neglected, the changes of chamber pressure there were found to be well in line with the chamber deformation caused by propellant gas expansion. The calculation results revealed that the relative errors between the chamber pressure values predicted by the proposed method and the measured ones were in the range of 0.82%-7.88%, suggesting that the proposed method can effectively predict chamber pressure. The calculation error at the chamber position was large, reaching 7.88%, due to the neglect of the gap between the cartridge case and the chamber’s inside walls. The pressure in the barrel part between the chamber throat and the muzzle was satisfactorily predicted, with a minimum error of 0.82% and a maximum error of only 5.89% at the muzzle.