Low Pressure Conditions Research Articles

Rheological Behavior of Gassy Marine Clay: Coupling Effects of Bubbles and Salinity

Understanding the rheological behavior of marine clay is crucial to analyzing submarine landslides and their impact on marine resource exploitation. Dispersed bubbles in marine clay (gassy clay) and electrolytes in seawater (e.g., NaCl concentration of 0.47 M) significantly impacts rheological properties. Under low ionic strength and low pore water pressure conditions, dispersed bubbles have a strengthening effect on the yield stress and the viscosity of clays. This effect turns into a weakening effect when the pore water pressure reaches 300 kPa or the ionic strength exceeds 0.18 M. It was proposed that the effect of bubbles, whether strengthening or weakening, was determined by the size of bubbles with respect to the characteristic size of the particle structure formed by clay particles. A theoretical model was developed, which reasonably captures rheological behaviors of gassy clays.

Carbon dioxide hydrate formation synergistically enhanced by calcium hydroxide and tetrafluoroethane under low-pressure conditions

Carbon dioxide hydrate formation synergistically enhanced by calcium hydroxide and tetrafluoroethane under low-pressure conditions

Laboratory experiments of carbon mineralization potential of the main terrestrial basalt reservoirs in China

Against the background of realizing the goal of “carbon peaking and carbon neutrality”, using basaltic rocks for carbon mineralization is one of the most promising approaches to reduce the rise in atmospheric CO2 concentrations. This study conducted a series of experiments to assess carbon mineralization in nine basalt samples from the main terrestrial basalt reservoirs in China within CO2-H2O/brine-rock systems at low temperatures (≤35 °C). The results indicate that the secondary carbonates formed in the CO2-H2O/brine-basalt system are predominantly calcite rather than Mg-carbonate minerals at low temperatures (≤35 °C). Hence, at low temperatures (≤35 °C), basalt rich in Ca-bearing minerals promotes the formation of stable carbonate minerals more effectively than basalt containing Mg-bearing minerals. Furthermore, under conditions of low temperatures (≤35 °C) and pressures of approximately 3 MPa, the results suggest that alkaline olivine basalt, with a higher content of Ca-minerals and typical alkaline minerals (nepheline and Na-sanidine), exhibits the highest pH value and the highest amount of calcite. Hence, the alkaline minerals, nepheline and Na-sanidine, serve as pH buffers to increase the pH and promote the precipitation of calcite within CO2-H2O– basalt systems at low temperatures (≤35 °C). Among the nine evaluated basalts, basalt from the Shandong Linqu-Changle volcanic basin exhibits the highest rate of carbon mineralization at low temperatures (≤35 °C). Hence, Cenozoic alkaline olivine basalt from Shandong Linqu-Changle volcanic basin is one of the most promising basalt reservoirs in China for future in- situ carbonation. As for ex- situ carbonation, compared with olivine, diopside or Ca-plagioclase may be more appropriate for increasing ocean negative emissions.

Water distribution and barrier character of cement-based materials with paraffin emulsion under low-pressure and low-humidity conditions

Water distribution and barrier character of cement-based materials with paraffin emulsion under low-pressure and low-humidity conditions

Experimental and modeling study of the effect of cetane improver-coupled EGR on RP-3 kerosene spray ignition and emissions

ABSTRACT To improve the ignition quality of RP-3 kerosene as a single fuel for application in direct injection diesel engines, the effect of ignition improvers and exhaust gas recirculation (EGR) on the ignition and emission of RP-3 fuel was investigated. The ignition delays of three sets of fuels, pure RP-3, 1,2-dimethoxyethane(1,2-DME)/RP-3, and 2-ethylhexyl nitrate(2-EHN)/RP-3, were measured experimentally in a constant volume combustion chamber. The exhaust emissions (CO, CO2, HC, and NOx) were measured under different operating conditions, and the effect of EGR was evaluated. The kinetic analysis was performed by merging a new model. The results showed that the ignition delay of pure RP-3 fuel was shortened by 22.4% on average as the ambient pressure varied from 2.2 MPa to 4 MPa. 2-EHN promoted RP-3 ignition more effectively than 1,2-DME. The introduction of EGR in low-temperature and low-pressure conditions is more favorable for shortening the ignition delay. The addition of ignition improvers weakens the effect of EGR on ignition. Lower ambient pressures bring higher levels of emissions. 2-EHN has a more significant positive effect than 1,2-DME to reduce HC and CO emissions. 1,2-DME-doped fuels are prone to bring about a spike in NOx under high ambient temperatures. Kinetic analysis reveals that 2-EHN has a more significant effect on the first stage of ignition. For 1,2-DME/RP-3, the OH radical formation pathway is enriched with more low-temperature branched chain reactions originating.

Effect of pressure and current density on metastable argon dynamics in low-pressure Ar-O2 plasma

Abstract Non-thermal plasma demonstrates a significant enhancement in efficiency when oxygen is added into the plasma mixture, particularly in processes such as thin-film oxide deposition, poly film removal, and photoresist mask ashing. This study examines the behavior of metastable argon states (1s5 and 1s3) in Ar-O2 mixture plasma, generated by a 50 Hz pulsed DC power supply under low-pressure conditions ranging from 1 mbar to 7 mbar. The densities of metastable argon states were assessed at varying conditions of current density, argon concentration, and filling gas pressure, utilizing optical emission spectroscopy (OES). The argon emission line ratio technique was employed to determine the plasma parameters. Experimental results indicate that electron density increases with current density, driven by enhanced excitation and ionization processes, while higher argon concentrations facilitate efficient ionization. The declining trend of the electron density with an increase in filling gas pressure is attributed to higher-pressure collisional processes. Metastable argon atoms exhibit heightened density with increased current density and argon percentage but decrease with elevated pressure due to loss processes. The regulation of metastable states is crucial for processes like etching, surface modification, and sterilization, providing a crucial step to the optimization and enhancing these applications.

Design of High‐Tc Quaternary Hydrides Under Moderate Pressures Through Substitutional Doping

AbstractIn recent years, there has been considerable interest in exploring high‐temperature superconductors in hydrides at low‐pressure conditions. A series of quaternary XAZ2H16 compounds (X, A = La, Ca, Sr, Ba, Ac, Ce, Th, Na or K; Z = Be, B, Si or P) are constructed based on ternary Fm‐3m LaB/BeH8‐type structure. Eight hydrides are found to be thermodynamically stable, with LaThBe2H16 and AcBaSi2H16 exhibiting lower pressures of 92 and 81 GPa, respectively. All investigated hydrides display dynamical stability at pressures below one million atmospheres, with LaThBe2H16 remaining stable even as low as 8 GPa. Moreover, LaSrB2H16, AcBaSi2H16, AcSrSi2H16, and Ba2SiPH16 exhibit clear covalent bonding characteristics between Z and H atoms, while Be atoms tend to form ionic bonds with H atoms. Electron‐phonon coupling calculations indicate that all of these quaternary hydrides have potential as superconductors. LaThBe2H16, AcBaSi2H16, AcSrSi2H16 and YCeBe2H16 exhibit superconducting transition temperatures (Tcs) of 126, 137, 123, and 104 K at 10, 30, 30, and 45 GPa, respectively, while LaYBe2H16 exhibits the highest Tc of 221 K at 75 GPa. These findings provide valuable insights for the search for high‐Tc superconductors under lower pressure conditions and encourage further exploration of polynary superconducting hydrides.

Geochemical Characteristics of Felsic Volcanic Rocks in Active Continental Margin above Ridge Subduction: A Case Study of the Neoproterozoic Suxiong Formation in the Western Yangtze Block

An N-S trending Neoproterozoic magmatic belt is preserved along the western margin of the Yangtze Block, which is characterized by predominant felsic and minor mafic-ultramafic rocks. However, four geodynamic models have been proposed to elucidate the formation of these rocks. In this paper, we present geochronological and geochemical data for dacite crystal tuff, rhyolitic welded tuff, and rhyolite from the Suxiong Formation. These findings, combined with the previously published Sm-Nd isotopic data, aim to provide robust constraints on the genesis of these felsic rocks and offer additional support for the geodynamic model of ridge subduction occurring beneath the western margin of theYangtze Block. Our study reveals that a fresh sample of dacite crystal tuff has a weighted average age of 813 ± 20 Ma. Major elemental data indicate that the samples have predominately peraluminous compositions. In addition, the rhyolites belong to the High-K Calc-alkaline Series and the dacite crystal tuffs are affiliated with the Calc-alkaline Series. They show seagull-shaped chondrite-normalized Rare Earth Elements (REE) patterns with negative Eu anomalies. Multi-element spider diagrams suggest they are enriched in Light Rare Earth Elements (LREE) and Large-Ion Lithophile Elements (LILE) and display Nb-Ta depletion. Additional geological, mineralogical, and geochemical clues suggest these rocks were derived from partial melting of associated Kangding Tonalite-Trondhjemite-Granodiorite (TTG) suites under low-pressure and high-temperature condition. This conclusion is also supported by the Sm-Nd isotopic compositions obtained from previous studies. The rocks have an A-type affinity and belong to A2-type group. On Rb-Hf-Ta triangular plot, they fall in the «volcanic arc» field and are thought to form at an «active continental margin». Moreover, these rocks are comparable in trace-element geochemistry to the rhyolites and dacites of Coast Range in western California, southern Alaska. In conclusion, we proposed that the 813 Ma felsic volcanic rocks of the Suxiong Formation were formed above a slab window driven by ridge subduction. This idea offers additional evidence for supporting a geodynamic model of ridge subduction existing along the western margin of the Yangtze Block during the Neoproterozoic era.

Evaluation of Pressure Effect on Accelerated Aging Tests of Polymer-Insulated Aircraft Wires

Most current international standards for qualifying polymer-insulated wires for aircraft applications rely on degradation tests conducted under standard pressure conditions. However, some wires are used in unpressurized areas and therefore need to withstand low-pressure conditions. In the technical literature, there is a shortage of data on this topic. This article focuses on accelerated wet arc tracking tests of insulated wires and evaluates three methods that assess the performance of surface discharges generated during degradation, based on the light emitted, under different pressure conditions in the range of 100 kPa–16 kPa. The experimental results presented in this paper show that the sensitivity of the proposed methods increases with atmospheric pressure, allowing a better quantification of the degradation effects at higher pressures. These results can also help to gain experience and understanding in how commercial optoelectronic sensors can be used to assess the insulation condition by analyzing the light generated by the surface discharges.

Quasi-Steady Water Droplet Heat- and Mass-Transfer With Ventilation, Blowing, and Radiation

Abstract A quasi-explicit analytical model of quasi-steady (QS) water droplet heat- and mass-transfer, including radiation, in a prescribed gaseous environment with velocity slip, i.e., gas flow around the droplet, and high mass-transfer-rate blowing effects has been developed. The model is an extension of an atmospheric science model used for cloud and fog droplets in dilute and near-saturation conditions with negligible velocity slip (ventilation flow) and blowing. The new model includes the effects of ventilation flow, blowing, and change in relative humidity or supersaturation across the diffusion layer surrounding the droplet. Comparisons show significant improvement in accuracy over the conventional model, particularly for conditions of low relative humidity, low pressure, and high radiative flux.

Research on Transient Characteristics of an Aviation Starter Motor Under Low Temperature and Pressure

To enhance the performance of aviation piston engine starters in high-altitude environments, this study investigated their transient starting characteristics under low-temperature and low-pressure conditions using a high-altitude simulation chamber. Experiments were conducted across ambient temperatures from −60 to 15 °C and pressures from 35 to 95 kPa. The results show that the ambient temperature significantly impacts the transient characteristics of the motor, particularly at the initiation stage, whereas pressure has a weaker effect. For every 5 °C drop in temperature, the peak starting current increases by 1.95 A. From 15 to −60 °C, the maximum difference in the starting current pulse width is 11.64 ms. Furthermore, as the ambient temperature decreases, the average current after the motor stabilizes increases, and the average speed decreases.

Experimental study on basic characteristics of high performance plasma jet actuator

A high performance plasma jet actuator (HPJA) has been developed to address the challenges of ignition difficulty and low combustion efficiency in ramjet combustors operating under transition mode and low pressure conditions. HPJA is capable of realizing the functionalities of large-area hot jet ignition, fuel activation, and enhanced combustion. The discharge characteristics, fuel activation characteristics, spray characteristics, ignition and assisted combustion characteristics of HPJA was investigated through experimental methods. The discharge power of HPJA initially increases, then decreases, and subsequently increases with the rise in carrier gas flow. Following fuel injection, the discharge power exhibits a similar trend but with an increased magnitude, showing a 21.9 % enhancement when Air = 30 SLM. HPJA has the capability to activate fuel, generating small molecule flammable substances such as H2 and CH4. The flow rates of fuel and nitrogen have a significant impact on the effective cracking rate. As the fuel flow increases, the effective cracking rate decreases. Similarly, with an increase in nitrogen flow, the effective cracking rate initially decreases before increasing again. Upon activation of HPJA excitation, there is a notable reduction in the particle diameter of outlet fuel, leading to a 41.5 % decrease in D32 under WN2 = 40 SLM and Fuel = 0.25–1.25 g/s. Based on the stability of the HPJA outlet's hot jet production, it is categorized into two operational modes: fuel excitation mode and jet evolution mode. As the carrier gas flow increases, the fuel required for HPJA to transition into the jet evolution mode decreases, thereby facilitating rapid ignition functionality. Under Ma = 0.2 and T∗ = 320 K conditions, as P∗ decreases from 107 kPa to 45 kPa, HPJA is more prone to forming a stable hot jet, resulting in an 88.9 % reduction in the fuel needed to enter the jet evolution mode.

Enhancing the Thermal Stability and Combustion Performance of NC-Based Propellants via Bu-NENA Modification.

In this paper, a series of insensitive smokeless nitrocellulose (NC)-based propellants were prepared through the absorption rolling method. Their thermal stability was rigorously assessed via vacuum stability test (VST), and their thermal reactivity of the propellant was comprehensively investigated and compared using the thermogravimetric analysis (TG)/differential scanning calorimetry (DSC) technique. Additionally, the combustion characteristics were meticulously analyzed by a constant-volume combustion diagnosis system. The experimental results showed that the thermal stability of the propellant was significantly enhanced when N-butyl-N-nitratoethyl nitramine (Bu-NENA) was used to partially or fully replace nitroglycerin (NG). However, an increase in Bu-NENA content corresponded with a decrease in the burning rate of the propellant. The catalytic effects observed in propellants varied markedly, influencing the composition of the products formed during thermal decomposition. Specifically, substituting 50 and 100% of NG with Bu-NENA resulted in reductions in the decomposition heat release of 96.2 and 258 J·g-1, respectively. Furthermore, the introduction of the catalyst significantly increased the burning rate under low-pressure conditions. For instance, at 2 MPa, the burning rate of Bu-0503 increased from 1.78 to 5.23 mm·s-1. A lower content of Bu-NENA was associated with a more luminous flame, while substituting 50 and 100% of NG with Bu-NENA led to decreases in flame temperature by 222 and 535 °C, respectively. The observed decrease in the flame temperature is attributed to the heat absorption during the volatilization of Bu-NENA, leading to a reduction in the thermal feedback of the flame.

Preservation of Microorganisms (Chroococcidiopsis sp. 029) in Salt Minerals under Low Atmospheric Pressure: Application to Life Detection on Mars

Salt minerals on Mars represent a promising target for investigating potential past surface and subsurface life. Terrestrial salt minerals have been shown to incorporate microorganisms within crystals. However, the effect of Mars’s low atmospheric pressure on the preservation of microorganisms in salt minerals during their formation remains unclear. Here we investigated the interactions between microorganisms (Chroococcidiopsis sp. 029) and crystals of halite (NaCl), epsomite (MgSO4·7H2O), and gypsum (CaSO4·2H2O) during the rapid evaporation of brines under simulated Martian atmospheric pressure. Parallel experiments were conducted under terrestrial pressure for comparison. Halite, epsomite, and gypsum formed under both terrestrial and low-pressure conditions, though crystal morphologies varied depending on the pressure. Microorganisms were identified within fluid inclusions or as solid inclusions in the crystal matrix. Halite crystals exhibited a greater propensity to incorporate cells under low pressure compared to terrestrial pressure, while the entrapment of cells in epsomite was similar under both conditions. In contrast, significantly fewer cells were trapped in gypsum crystals under low pressure. The results demonstrate the feasibility of cell entrapment in salt minerals formed by rapid evaporation under low-pressure conditions on Mars, and atmospheric pressure exerts distinct influences on different types of salts. The variation in fluid inclusion size in halite under different pressures even shows promise as a possible paleobarometer. Our findings suggest that halite is the most promising candidate for preserving potential Martian life and could be an excellent target for future Mars sample return missions.

High temperature capture of CO2 on Li4SiO4 sorbents via a simple dry ball-milling coupled with K2CO3 physical addition

The reversible CO2 absorption/desorption of lithium orthosilicate (Li4SiO4) sorbents holds potential for high temperature capture of CO2 from hot flue gases, sorption-enhanced reforming and solar thermochemical energy storage. In this study, we have prepared a series of Li4SiO4 sorbents using a combination of K2CO3 addition and dry ball-milling procedure to improve the relatively slow kinetics under low CO2 partial pressure conditions. The synergistic effects of dry ball-milling and K2CO3 addition on the intrinsic properties of Li4SiO4 sorbents were explored by thermogravimetric analysis and structural characterizations. Thermogravimetric analysis indicate that the highest CO2 uptakes were achieved with dry ball-milling combined with K2CO3 physical addition. The structural characterizations further reveal that this sorbent (P-3K-1.5 M) had the smallest crystallite/particle size, largest surface area, and highest availability of surface alkaline-sites. The kinetics analysis also demonstrates that P-3K-1.5 M exhibited the fastest sorption kinetics during a double process. Additionally, P-3K-1.5 M maintained a high capacity over 10 sorption/desorption cycles. Therefore, this synthesis technique, which is simple, cost-effective, and easily scalable, shows great promise for high-temperature CO2 capture.

The Neoarchean granitoids in the Yanlingguan area, western Shandong, North China Craton record the transition from TTG to K-rich granitoids

The Neoarchean is an important period of continental crustal growth worldwide. Determining how the continental crust increases in size and was finally cratonized at the end of the Archean is therefore an important scientific issue in geology. This study involved field investigations, SHRIMP U-Pb zircon dating, zircon in situ Hf isotopic analysis, and whole-rock geochemistry of Neoarchean granitoids at Yanlingguan, a typical Neoarchean area in the western Shandong granite-greenstone belt, North China Craton. Three samples of diorite/TTG that occur as enclaves in monzogranite record the oldest magmatic zircon 207Pb/206Pb ages of 2738–2731 Ma. They have low ΣREE (total REE) contents (37.5–72.4 ppm), low (La/Yb)n (8.9–25.5) and variable Eu/Eu* (0.90–1.86). The Xinfushan trondhjemite has a weighted mean 207Pb/206Pb age of 2599 ± 4 Ma for magmatic concordant or near-concordant zircons from six samples. The trondhjemites have large REE variations, with ΣREE, (La/Yb)n, and Eu/Eu* being 36.3–150.9 ppm, 23.9–91.1 and 0.57–2.00, respectively. The Lianhuashan monzogranite has a weighted mean 207Pb/206Pb age of 2502 ± 6 Ma for magmatic concordant or near-concordant zircons from four samples. These rocks have ΣREE contents, (La/Yb)n and Eu/Eu* of 42.9–573.7 ppm, 2.4–89.1 and 0.31–1.20, respectively. The geochemisal data indicate that the 2.7 Ga diorite/TTG rocks formed by fractional crystallization of mafic magma under low-pressure conditions. In contrast, the 2.6 Ga trondhjemites were most likely formed by a mixture of magmas derived from partial melting of low-K mafic and the earlier tonalitic rocks; whereas the 2.5 Ga monzogranites were derived by partial melting of the earlier TTG rocks, with addition of some sedimentary material. These events commenced with the subduction and melting of early Neoarchean oceanic crust, likely influenced by mantle plume activity, through an increase in crustal melting and consequent increase in the K2O/Na2O ratio in the 2.6 Ga TTG, and culminated in the production of the widespread generation of K-rich monzogranites at 2.5 Ga. Western Shandong thus underwent an increase in crustal maturity as it transitioned from TTG-dominated magmatism to K-rich granite, marking cratonization of the North China Craton at the end of the Neoarchean.

Development of a Master Equation-Based Microkinetic Model to Investigate Gas Phase Cluster Reactions Across a Wide Pressure and Temperature Range.

Small gas-phase metal clusters serve as model systems for complex catalytic reactions, enabling the exploration of the impacts of the size, doping, charge state and other factors under clean conditions. Although the mechanisms of reactions involving metal clusters are known in many cases, they are not always sufficient to interpret the experimental results, as those can be strongly influenced by the chemical kinetics under specific conditions. Therefore, our objective here is to develop a model that utilizes quantum chemical computations to comprehend and predict the precise kinetics of gas-phase cluster reactions, particularly under low-pressure conditions. In this study, we demonstrate that master equation simulations, utilizing reaction paths computed through quantum chemistry, can effectively elucidate the findings of previous experiments. Furthermore, these simulations can accurately predict the kinetics spanning from low-pressure conditions (typically observed in gas-phase cluster experiments) to atmospheric or higher pressures (typical for catalytic experiments). The models are tested for simple elementary steps (Cu4+H2). We highlight the importance of the reaction mechanism simplification in Cu4 ++H2 and provide an interpretation for the previously observed product branching in Pt++CH4.

Pressure Transient Analysis for Fractured Shale Gas Wells Using Trilinear Flow Model

Shale gas, a low-permeability, unconventional resource, requires horizontal drilling and multi-stage fracturing for commercial production. This study develops a trilinear flow model for fractured horizontal wells in shale gas formations, incorporating key mechanisms such as adsorption, desorption, diffusion, wellbore storage, and skin effects. The model delineates seven distinct flow regimes, providing insights into gas migration processes and the factors controlling production. Sensitivity analyses reveal that desorption plays a critical role under low-pressure and low-production conditions, significantly enhancing gas transfer rates from the matrix to the fracture network and contributing to overall production. Monte Carlo simulations further highlight the variability in pressure responses under different input conditions, offering a comprehensive understanding of the model’s behavior in complex reservoir environments. These findings advance the characterization of shale gas flow dynamics and inform the optimization of production strategies.

Finding Diffusivity and Solubility of Impurities inside ILs By MD

Ionic liquids (ILs) are promising candidates for use in the semiconductor industry because of their unique and tunable physicochemical properties. They are a novel class of salts with desirable features such as being in liquid phase at room temperature, nonflammability, high ionic conductivity, high thermal stability, and low to negligible vapor pressures. Their physical, chemical, solubility, transport, and solvation properties can be tuned by altering the cations or anions to tailor for applications in the semiconductor industry, including the process of liquid/gas separations, extraction of impurities, and cleaning under vacuum. Selecting suitable ILs to enhance the efficiency of the target semiconductor processes and tools is crucial.One possible application is to use ILs as a barrier or protective liquid film that does not evaporate in low-pressure conditions. For this application, we need a better understanding of the molecular scale of the behavior of the ILs at different temperature ranges. To develop such a new process, the knowledge of absorbing/desorbing impurities (such as O2, CO2, and H2O, including their mixtures and other organic materials) in the ILs and their transport (diffusion coefficients) properties inside the ILs at different temperatures is essential from the surface protection film point of view. This work seeks to answer these essential questions at the nanometer scale by showing the results from molecular dynamics (MD) simulations of the diffusivity and solubility of impurities inside ILs. Examples of MD simulation models for this study are shown in Figure 1, where impurities with the same concentration are placed on both sides of ILs, and the transport behavior of impurities inside ILs is extracted. From these nanoscale results, we can better understand and predict the diffusivity and solubility of impurities inside ILs and find the conditions at which impurities can be removed from ILs for recycling purposes. Figure 1

Numerical Analysis of Knudsen Number of Helium Flow Through Gas-Focused Liquid Sheet Micro-Nozzle

This work aims to verify whether the continuum mechanics assumption holds for the numerical simulation of a typical sample delivery system in serial femtosecond crystallography (SFX). Knudsen numbers were calculated based on the numerical simulation results of helium flow through the gas-focused liquid sheet nozzle into the vacuum chamber, representing the upper limit of Knudsen number for such systems. The analysed flow is considered steady, compressible, and laminar. The numerical results are mesh-independent, with a Grid Convergence Index significantly lower than 1% for global and local analysis. This study is based on an improved definition of the numerical Knudsen number: a combination of the cell Knudsen number and the physical Knudsen number. In the analysis, no-slip boundary and low-pressure boundary slip conditions are compared. No significant differences are observed. This study justifies using computational fluid dynamics (CFD) analysis for SFX sample delivery systems based on the assumption of continuum mechanics.