Gas Expansion Research Articles

Effects of spherical Al2O3 grades on crack initiation of thermal conductive silicone pads under high-temperature aging

ABSTRACT In this paper, the rule and mechanisms of crack initiation and propagation in the aging process of thermal conductive silicone pads (TCSP) were investigated by designing Al2O3 particle grading schemes with different particle sizes and mass ratios. Scanning electron microscope and energy dispersive spectrometer analysis showed that TCSP prepared with Al2O3 particles of various sizes according to the gradation ratio had the best anti-aging effect at high temperatures. At this time, the aging was mainly due to the aging degradation of the polymer matrix; When the proportion of small-size Al2O3 particles increases, aggregates and pore defects appear in TCSP. At this time, the main reason for its aging is that the high-temperature expansion of gas in pore defects accelerates the aging degradation of the polymer matrix; When the proportion of small-sized Al2O3 particles decreases, a large number of holes appear in TCSP and the coverage rate of the polymer matrix on Al2O3 particles decreases. The main reason for the high-temperature aging crack is that the gas between the holes expands at high temperature, resulting in the rapid extension of the crack and the polymer matrixes falling.

Application of High-Pressure Gas Expansion Rock-Cracking Technology in Hard Rock Tunnel near Historic Sites

In order to study the applicability of high-pressure gas expansion rock-cracking technology in hard rock tunnel near historic sites, theoretical analysis, field tests as well as vibration monitoring are conducted to obtain suitable rock mass cracking parameters for tunnel excavation. The results show that the ideal effect of rock mass cracking can be achieved with the cutting mode of “central vertical empty hole + double wedge cutting hole” and the auxiliary hole network parameter of “0.8 m × 0.7 m”. The measured vibration velocity is less than 0.1 cm/s at the monitoring point 60 m away from the tunnel face in the field test, which meets the vibration control requirements of the historic sites in the process of tunnel excavation. The research results show that as long as there is a high quality of hole plugging and no punching, the high-pressure gas expansion rock-cracking technology has the advantages of little vibration, low noise and less flying rocks, which provides a technical reference for the excavation of hard rock tunnels near ancient buildings and historic sites.

Microscopic experiment study on mechanisms of oil-gas interaction and CO2 -surfactant flooding with different temperatures and pressures

For secondary and tertiary oil recovery processes, the interfacial interactions between injected gas and crude oil contributes significantly at the pore-scale. We experimentally examine the effect of temperatures, pressures and surfactants on interfacial interaction, contact angle and oil displacement efficiency of CO2 flooding at the pore-scale using microfluidics. Two types of flow channel designs are utilized in this study, blind end of direct channels and curved channels with different diameters. The results indicate that increasing pressure and adding surfactants can promote the contact between oil and gas and reduce the interfacial tension, which has a certain impact on oil displacement efficiency. In the process of gas flooding, CO2 dissolution, expansion and miscibility are the key oil-gas interactions. The results of experiments in curved and direct channels show that the curved channels increase the resistance of fluid flow and limit the contact between CO2 and oil. And with the decrease of the porous medium radius, the capillary action in the pores increases, and the higher the viscous force needed for displacing the oil, which will affect the interaction between oil and gas and the oil recovery in micro pores. Then, two non-ionic alkoxylated surfactants (i.e. ethylene glycol butyl ether and Span 80) were selected to enhance the interaction between CO2 and crude oil. The presence of surfactants increases the solubility of CO2 in crude oil, which reduces the interfacial tension of the system and results in higher oil recovery.

Plasma-induced exfoliation in NiMn-layered double hydroxides for enhanced oxygen evolution reaction activity

As one of typical two-dimensional nanomaterials, layered double hydroxides (LDHs) exhibited unique properties in oxygen evolution reaction (OER). In this work, NiMn-LDHs were successfully exfoliated to nanosheets by cold plasma treatment. The exfoliation mechanism was proposed, that is, high energy electrons produced by plasma excited the intercalated water in host layers to generate H·, HO· and H+. The intermediate combined with CO32- to produce CO2 gas, which induced gas expansion to achieve the exfoliation of NiMn-LDHs. A large number of oxygen vacancies on LDHs nanosheets were also generated in the process of exfoliation. The increased active sites improved the intrinsic activity in OER. After plasma treatment was conducted for 30 min, the NiMn-LDHs exhibited high OER performance with an overpotential of 357 mV to achieve a current density of 10 mA cm–2 and a Tafel slope of 60.1 mV dec–1 in alkaline conditions.

Plasma synthesis of oxygen vacancy-rich CuO/Cu2(OH)3NO3 heterostructure nanosheets for boosting degradation performance.

Defect regulation and the construction of a heterojunction structure are effective strategies to improve the catalytic activity of catalysts. In this work, the rapid conversion of CuO to Cu2(OH)3NO3 was achieved by fixing nitrogen in air as NO3- using dielectric barrier discharge (DBD) plasma. This innovative approach resulted in the successful synthesis of a CuO/Cu2(OH)3NO3 nanosheet heterostructure. Notably, the samples prepared using plasma exhibit thinner thickness and larger specific surface area. Importantly, oxygen vacancies are introduced, simultaneously forming heterojunction interfaces within the CuO/Cu2(OH)3NO3 structure. CuO/Cu2(OH)3NO3 using plasma effectively degraded 96% of methyl orange within 8 min in the dark. The degradation rate is 81 and 23 times that of CuO and Cu2(OH)3NO3 using hydrothermal methods, respectively. The high catalytic activity is attributed to the large specific surface area, the abundance of active sites, and the synergy between oxygen vacancies and the strong heterojunction interfacial interactions, which accelerate the transfer of electrons and the production of reactive oxygen species (˙O2- and ˙OH). The mechanism of plasma preparation was proposed on account of microstructure characterization and online mass spectroscopy, which indicated that gas etching, gas expansion, and the repulsive force of electrons play key roles in plasma exfoliation.

Free and enclosed inertial active gas.

In this work, the free expansion of an inertial active gas in three dimensions made of spherical non-interactive active Brownian particles with both translational and rotational inertia (IABPs) is studied. After elucidating the active particles' orientational correlation in three dimensions by employing a Fokker-Planck formalism, the diffusion, mean-square speed, persistence length, reorientation time, Swim and Reynolds pressures and total pressure of this system, are obtained theoretically and corroborated by performing Langevin dynamics simulations. Afterwards, a numerical study on particles' distribution and the mechanical pressure exerted by the active gas enclosed in a cubic box and its dependence on inertia is also carried out. This experiment highlights two important observations: first, as inertia in the system grows while fixing activity, a more uniform particle distribution within the box is achieved. In other words, the classical accumulation of active particles at the walls is seen to be suppressed by inertia. Second, an active gas with translational and rotational inertiae and made of spherical particles still has a state equation which is offered here. This is supported by the fact that both the mechanical pressure definition and the bulk pressure definition as the trace of the swim and Reynolds stress tensors, coincide in the thermodynamic limit.

Peak heat flux prediction of hypersonic flow over compression ramp under vibrationally excited free-stream condition

In hypersonic shock tunnel experiments, the high-temperature reservoir gas expands and accelerates so rapidly that there is not enough time for vibrational energy relaxation. As a result, thermal nonequilibrium gas flow is frequently encountered in the test section, and this significantly affects the measured heat flux. In this paper, hypersonic compression-ramp flows are studied numerically to investigate the effect of incomplete vibrational energy accommodation on the separation flow structure and peak heat flux in the reattachment region under low-to-medium Reynolds number and high Mach number conditions. Numerical results and theoretical analysis suggest that the vibrational energy accommodation has no noticeable impact on the length scale of the separation zone, but strongly influences the peak heat flux of the separated ramp flows. Decomposing the peak heat flux into translational–rotational energy and vibrational energy components, qtr and qv, respectively, we find that qv/qtr characterizes the nonequilibrium degree of the vibrational energy accommodation. A formula for predicting the peak heat flux is then proposed, taking the effect of incomplete vibrational energy accommodation into consideration. Finally, surface heat flux measurements in a hypersonic shock tunnel indicate that a deviation of up to 13% in total peak heat flux could arise if vibrational energy accommodation is not considered under the vibrationally excited free-stream condition.

About rationale for the selection of the cooling capacity of the turbodetander unit in the process of gas preparation

In gas condensate fields, low-temperature separation process is mainly used for primary processing of gas. Cooling of well products in gas preparation systems is achieved by throttling them. As the reservoir pressure decrease, the amount of energy obtained decreases. This worsens the conditions for the preparation of gases. Therefore, raises a need to use additional energy sources. Analysis of the operating modes of gas treatment plants has shown that the energy obtained during the expansion of gas can be used rationally. Calculations have shown that the gas temperature at the outlet of turbodetander units during adiabatic expansion provides the required dew point for water and hydrocarbons. Keywords: gas; condensate; turbodetander; gas expansion; polytrophic; adiabatic; cold productivity; dew point.

Moser–Tardos resampling algorithm, entropy compression method and the subset gas

We establish a connection between the entropy compression method and the Moser–Tardos algorithmic version of the Lovász local lemma through the cluster expansion of the subset gas. We also show that the Moser–Tardos resampling algorithm and the entropy compression bactracking algorithm produce identical bounds.

Oxidation resistance and thermal shock behavior of tri-layer Si/Si–Yb2SiO5/Yb2SiO5–SiC environmental barrier coatings at 1300 °C

The objective of this preliminary study is to improve the thermal shock and oxidation resistance of environmental barrier coatings by doping adjustment of the coating composition. A novel tri-layer Si/Si–Yb2SiO5/Yb2SiO5–SiC coating was fabricated on the surface of SiC substrate using atmospheric plasma spraying. These coated samples were subjected to 1-h thermal shock test between 1300 °C and room temperature in air. The oxygen diffusing through the cracks into the inner coating was consumed by SiC and Si to form SiO2, which reacts with Yb2SiO5 to form Yb2Si2O7. The oxidation of SiC was accompanied by volume expansion and volatilization of gas, and resulted in the formation of pores and mud-cracks. The Si with high surface area in the Si–Yb2SiO5 layer has higher oxidation rate, which causes the formation of spallation cracks, but no delamination after 800 cycles. Results showed that coating has excellent oxidation and thermal shock resistance at 1300 °C.

Multiscale and multiphysics production forecasts of shale gas reservoirs: New simulation scheme based on Gaussian pressure transients

Common numerical solutions for production rate forecasting of shale reservoirs have a limited capability to describe the dynamics of fluid mass transfer during a pressure depletion cycle due to production with hydraulically fractured well systems. The pressure drawdown imposed by the well system triggers continuous expansion of free gas in the larger pores, while molecular diffusion predominates in the smaller pores. The declining reservoir pressure leads to the closure of larger pores, which gives further significance to molecular diffusion as a component of the mass transport process. To capture these multiphysics mechanisms, pressure-diffusion and molecular-diffusion forms of the diffusivity equation, discretized in space and time, were simultaneously solved to simulate mass transfer dynamics and kinematics in shale formations. This new approach uses a Gaussian probability function to describe the advance rate of both types of diffusion processes, creating a unique scheme for simulating shale gas reservoirs based on physical parameters that could be either measured or characterized. The adopted algorithms successfully provide solutions that can match the typical shale production profiles. Results are sensitive to the essential reservoir parameters of pressure depletion, matrix permeability, organic content, and local heterogeneity. The simultaneous solution of molecular and pressure diffusivity equations reveals their interdependencies. The production peaks early and then rapidly declines with a growing effect of pore compaction. The flux of the sorbed phase contributes to the production rate by some factor that is determined by the sorption capacity of the organic matter. The methodology provided in this study can be utilized to simulate mass transport in shale reservoirs and predict hydrocarbon production rates, which may greatly aid asset management decisions and maximization of the ultimate recovery.

Nanometric MnO2 and MnO2‐Graphene Oxide Materials Enabled by a Solvent‐Assisted Synthesis and Their Application in Asymmetric Supercapacitors

Conventional manganese oxide (MnO2)‐based supercapacitors struggle to achieve theoretical capacitance due to the material's low conductivity and large particle size. Consequently, researchers have improved MnO2's properties by incorporating conductive carbonaceous materials to obtain high‐performance composite materials. Herein, the full process of engineering a MnO2‐graphene oxide (GO) composite and its application as a positive electrode for asymmetric supercapacitors (ASC) is presented. First, GO using a novel gas expansion precursor allowing an efficient chemical exfoliation of pristine graphite is synthesized. Afterward, size‐weakened MnO2 nanoparticles are synthesized and deposited onto the GO sheets by a self‐assembly redox reaction method using different MnO2/GO mass ratios. Multiple characterization methods are used to investigate the textural and structural properties of each material. A general electrochemical characterization is conducted using a three‐electrode cell; therefore, the synthesized MnO2‐GO composite achieves 150 F g−1 at 10 mV s−1. Furthermore, an ASC in an aqueous electrolyte using GO and MnO2 or MnO2‐GO as negative and positive electrodes, respectively, is assembled. The fabricated ASC based on MnO2‐GO composite exhibits a high specific capacitance of 38 F g−1 at 1 A g−1, excellent cycling stability after 36 000 cycles, and a steady electrochemical impedance behavior after 120 h of floating.

Numerical simulation of carbon separation with shock waves and phase change in supersonic separators

The current study evaluated a potential carbon separation method. Based on engineering thermodynamics, heat transfer and phase transition dynamics, a mathematical model is proposed to predict the phase change in high pressure supersonic flow, and a flue gas model after dehydration, desulfurization and denitration is established. The flow features with shock waves and spontaneous condensation in the supersonic separator are clarified, the influence of flow model on shock waves and flow features is quantified, and the energy recovery process with phase change is studied. The results show that flue gas enters the supercooled state near the throat, reaches Wilson point at x = 0.077 m, and the nucleation rate surges from 0 to 4.46 × 1020 m−3 s−1. When vapor molecules reach the surface of droplets, droplets grow, and latent heat is transferred from droplets to the vapor phase, resulting in condensation wave. A shock wave is generated at the diffuser inlet, and the flow and liquid phase parameters change abruptly after the shock wave. The single-phase model incorrectly predicted the separator refrigeration capacity, flue gas expansion capacity, location and intensity of the shock wave, and the maximum deviation is up to 65.5%. Excessive improvement of pressure recovery efficiency results in reducing the liquefaction capacity of the separator.

Gas expansion caused by formation uplifting and its effects on tight gas accumulation: A case study of Sulige gas field in Ordos Basin, NW China

Gas expansion caused by significant exhumation in the Sulige gas field in the Ordos Basin since Late Cretaceous and its effects on hydrocarbon accumulation have been investigated systematically based on comprehensive analysis of geochemical, fluid inclusion and production data. The results indicate that gas volume expansion since the Late Cretaceous was the driving force for adjustment and secondary charging of tight sandstone gas reservoirs in the Sulige gas field of the Ordos Basin. The gas retained in the source rocks expanded in volume, resulting in gas re-expulsion, migration and secondary charging into reservoirs, while the gas volume expansion in the tight reservoirs caused the increase of gas saturation, gas-bearing area and gas column height, which worked together to increase the gas content of the reservoir and bring about large-scale gas accumulation events. The Sulige gas field had experienced a two-stage accumulation process, burial before the end of Early Cretaceous and uplifting since the Late Cretaceous. In the burial stage, natural gas was driven by hydrocarbon generation overpressure to migrate and accumulate, while in the uplifting stage, the gas volume expansion drove internal adjustment inside gas reservoirs and secondary charging to form new reservoirs. On the whole, the gas reservoir adjustment and secondary charging during uplifting stage is more significant in the eastern gas field than that in the west, which is favorable for forming gas-rich area.

A Massive Star Is Born: How Feedback from Stellar Winds, Radiation Pressure, and Collimated Outflows Limits Accretion onto Massive Stars

Massive protostars attain high luminosities as they are actively accreting and the radiation pressure exerted on the gas in the star’s atmosphere may launch isotropic high-velocity winds. These winds will collide with the surrounding gas producing shock-heated (T ∼ 107 K) tenuous gas that adiabatically expands and pushes on the dense gas that may otherwise be accreted. We present a suite of 3D radiation-magnetohydrodynamic simulations of the collapse of massive prestellar cores and include radiative feedback from the stellar and dust-reprocessed radiation fields, collimated outflows, and, for the first time, isotropic stellar winds to model how these processes affect the formation of massive stars. We find that winds are initially launched when the massive protostar is still accreting and its wind properties evolve as the protostar contracts to the main sequence. Wind feedback drives asymmetric adiabatic wind bubbles that have a bipolar morphology because the dense circumstellar material pinches the expansion of the hot shock-heated gas. We term this the “wind tunnel effect.” If the core is magnetized, wind feedback is less efficient at driving adiabatic wind bubbles initially because magnetic tension delays their growth. We find that wind feedback eventually quenches accretion onto ∼30 M ⊙ protostars that form from the collapse of the isolated cores simulated here. Hence, our results suggest that ≳30 M ⊙ stars likely require larger-scale dynamical inflows from their host cloud to overcome wind feedback. Additionally, we discuss the implications of observing adiabatic wind bubbles with Chandra while the massive protostars are still highly embedded.

Numerical study of the influence of different water depths on the muzzle flow characteristics of machine gun

The mathematical and physical models of the underwater submerged gun are established to study the flow field distribution characteristics of the gun muzzle at different water depths. The Schnerr–Sauer cavitation model and the realizable k–ω transport turbulence model based on the Reynolds-averaged Navier–Stokes method are employed. The muzzle flow field for the 12.7 mm gun that is submerged launched underwater is numerically simulated by combining user-defined functions and overlapping mesh technology. The flow characteristics of the density, velocity, and pressure fields at the gun muzzle at different water depths are analyzed in detail. The results show that the muzzle flow morphology depends mainly on the pressure at different water depths. The muzzle flow field distribution in deep water is more flat due to the high value of water pressure, which limits the expansion of the muzzle gas, and the range of the velocity field of the muzzle flow field at 100 m is one time smaller than that at 1 m.

Some Thoughts about Infrared Radiation Response Characteristics during Loading of Sandstone Samples

The infrared radiation response characteristics and mechanisms of sandstone samples under uniaxial compression were investigated using infrared thermal imaging and strain measurement techniques. The stress–strain curves were divided into different damage stages (i.e., crack closure, elastic deformation, stable crack growth, unstable crack growth, and post-failure) by the damage thresholds determined using the transverse and vertical strains. Experimental results show that the infrared radiation response characteristics of sandstone include the superposition of different mechanisms, which lead to either temperature increase or decrease. The response mechanisms of infrared radiation vary depending on the damage stage. During crack closure and elastic deformation stage, temperature variations are mainly governed by thermoelastic effects and the nearly adiabatic compression of air in the pore space. In the stable and unstable crack growth phase, the temperature variations are dominated by two reverse acting processes: heat production by frictional sliding and cooling by the expansion of gases in pore spaces. This leads to complex inhomogeneous radiation and consequently temperature distribution at the sample surface with local hotspots.

Planar Gas Expansion under Intensive Nanosecond Laser Evaporation into Vacuum as Applied to Time-of-Flight Analysis.

A computational investigation of the dynamics of gas expansion due to intense nanosecond laser evaporation into vacuum has been carried out. The problem is solved in a one-dimensional approximation, which simplifies calculations and at the same time allows one to analyze the main features of the expansion dynamics. For analysis we use three different approaches. Two of them are based on kinetic analysis via the direct simulation Monte Carlo (DSMC) method and numerical solution of the model Bhatnagar-Gross-Krook (BGK) equation. The third one focuses on derivation of an analytical continuum solution. Emphasis is placed on the analysis of the velocity distribution function and the average energy of particles passing through the time-of-flight detector on the normal to the evaporation surface, which is important for interpreting experimental measurements. The formulated problem is quite difficult as the considered flow is time-dependent, contains discontinuities in boundary conditions and involves large variations of local Knudsen numbers as well as steep gradients of the velocity distribution function. Data were obtained on the particle energy in the time-of-flight distribution for the range of regimes from the free molecular flow to continuum one. The maximum attainable average energy of particles in the time-of-flight distribution is determined. The non-monotonicity of the energy increase was found, which is explained based on analysis of the velocity distribution of particles.

Experimental and numerical investigation of bubble evolution and bubble wall fluctuation mechanism during water entry of flared cavity

Most of the previous research on water entry focused on simple objects with “closed surface and regular shape”, such as wedges and disks. Only a few studies have investigated the water entry of complex structures with “surface cavity and irregular shape”, such as typical spacecraft, which are summarized as flared cavity in this paper. The water entry of flared cavity is a strong nonlinear process coupled with multi phase media, during which the liquid flows into or out of the flared cavity, and the obvious phenomenon of bubble wall fluctuation will appear. In this study, we experimentally investigate the bubble evolution process and bubble fluctuation law in a flared cavity under different impact speeds. The evolution process of bubble shape is photographed by a high-speed camera, and the bubble evolution process is divided into four stages: bubble formation stage, bubble development stage, bubble contraction stage and bubble shedding stage. It is found that there is an obvious fluctuation phenomenon on the bubble wall during the bubble development stage, which is mainly because of gas expansion and compression in the structural cavity, and the wall fluctuation law is basically consistent with the gas expansion and contraction trend. It is also established that the dimensionless parameters R/H1 and H1/H2 can be good indicators to describe the bubble expansion and bubble shedding, the dimensionless bubble expansion parameter R/H1 is stable between 0.033 and -0.042, and the dimensionless bubble shedding parameter H1/H2 is stable between 0.062 and -0.069.

Energy, exergy and economic analyses of an optimal use of cryogenic liquid turbine expander in air separation units

Cryogenic liquid turbine expanders have emerged quite recently as a replacement for traditional Joule-Thomson valves in cryogenic processes for energy saving purpose. However, introducing a liquid turbine expander into the cryogenic air separation unit (ASU) can influence the operating points of ASU components, and the maximum benefits arising from the liquid turbine expander have not yet been reported. To fill such a gap, thermodynamic models are first established for ASU components, including the main air compressor, booster air compressor, cryogenic gas and liquid turbine expanders, main heat exchanger, cryogenic pump, and distillation column. To achieve the best possible use of the liquid turbine expander, an optimization method is developed by incorporating the thermodynamic models with the particle swarm optimization algorithm, in which the total minimization power consumption of ASU is the optimization goal while the flow rates and pressures of the high pressure air stream and the air stream drawn from the booster air compressor middle section together with the temperature of the medium pressure air stream exiting the main heat exchanger midway act as the optimization variables. Then, energy, exergy and economic analyses are conducted and the corresponding indexes are chosen to quantitatively evaluate the influence of the liquid turbine expander on the air separation process. For the case study, ASUs of 35000 Nm3/h oxygen production capacity with and without a cryogenic liquid turbine expander are optimized, respectively. The results show that the ASU total power saving through the use of liquid turbine expander is 4.2-fold its output shaft power; thus, the energy consumption of unit oxygen decreases by 2.12% and the overall exergy efficiency increases by 1%. In addition, the economic analysis shows that the period of return of the liquid turbine expander in the ASU is estimated to be 1.75 years.