Variation Of Gas Pressure Research Articles

Slope Stability Analysis Method of Unsaturated Soil Slopes Considering Pore Gas Pressure Caused by Rainfall Infiltration

The variation of pore gas pressure caused by rainfall infiltration is an important factor that leads to slope failures. The purpose of this study is to propose a new slope stability analysis method that considers pore gas pressure and examines the effect of airflow on slope stability by using a numerical method. A water-air two-phase flow analysis was conducted to investigate the distribution of pore air pressure, pore water pressure, and water saturation triggered by rainfall infiltration. Then the variation of the load resulting from pore gas pressure was incorporated into the slope stability analysis method based on the unsaturated soil shear strength theory and the residual thrust method to simulate the influence of airflow on the Tanjiahe landslide in China. In order to study the infiltration behavior with respect to initial saturation, water and gas flow analyses were performed considering various initial states of saturation under similar settings. Results showed that the pore gas pressure between the slope surface and the slip band clearly varied and that it decreased during the process from the slide bed to the deep direction. Then, the pore water pressure formed in the saturated zone was transferred by the airflow to the slope toe. As a result, because the pore gas pressure gradient increased the thrust of the slide mass, the safety factor decreased over time. Moreover, in the first step, the magnitude of infiltration decreased with an increase in initial saturation, while when the magnitude dropped to the minimum value, it then went up with an increase in initial saturation. The maximum value was usually reached at a saturation degree of 0% or 100%. When evaluating slope stability, the safety factor obtained by the slope stability analysis method that considered the water-gas coupling effect was much lower than when it was not considered during the process of a similar seepage. The impact on the slope failure was significant and may provide a practical reference for hazard assessments to control rainfall-induced landslides.

Prospects for Developing Pressure and Tactile Sensors Based on Surface Plasmon Resonance

In this work, one examines the prospects of using the surface plasmon resonance (SPR) effect in the Otto configuration for pressure and deformation sensing. An open Otto chip device was employed, and the chip was characterized by the use of an automated reflectometer operating at a wavelength of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\boldsymbol {\lambda } = 975.1$ </tex-math></inline-formula> nm. The active area of the device was characterized by reflectometry-based profilometry. Significant modulation of the SPR effect due to a variable gas pressure was observed at a fixed point on the device’s active area. A gap reduction to approximately 50% of its nominal value was observed when the gas pressure changed from 1.7 to 0.28 bar. In addition, profilometry characterization in conjunction with a rigorous regression analysis allowed determining, unambiguously, the gap profile of the device under fixed stress. The results indicate that the technique is feasible for either pressure or tactile sensing applications.

Study on Natural Gas/Diesel Dual-fuel Engine Energy Ratio: Effect of Natural Gas Injection Parameters

Natural gas has been a promising demand for several years in Indonesia as a fuel for a diesel engine by converted into a natural gas/diesel dual-fuel engine. However, determining the energy ratio of the diesel and natural gas fuel is important due to the engine performance and emissions which affect the engine safety operation. This study presents the method to determine the natural gas and diesel fuel energy ratio on intake port natural gas injection mode through experiment. A direct injection diesel engine is converted to a natural gas/diesel dual-fuel engine by injecting natural gas into the intake port. The diesel injection parameters are unmodified for the experiment; besides the natural gas injection variations are studied to determine the energy ratio. Moreover, the engine is tested for low to high load conditions. However, natural gas injection duration, pressure, and injection timing variation affect the fuel energy ratio and indicated thermal efficiency (ITE). At low load, the optimum fuel energy ratio and ITE are achieved at a long injection duration (10 ms) and with advanced injection timing. Moreover, at high load, the optimum fuel energy ratio and ITE is achieved at high natural gas injection duration (12 ms), high injection pressure (3 bar), and advancing the injection timing.

Optimal design and its mixing process analysis of a novel rotor for claw vacuum pumps

Due to the particular structure of a pair of intermeshing claw rotors, the working process of claw vacuum pump includes an inevitable mixing process, which increases power consumption and reduces pump efficiency. In order to reduce the negative effects of the mixing process on pump performance, this paper presented a novel eccentric involute claw rotor (EICR) based on the performance analysis of the mixing process of the conventional claw rotor. A geometric model of the proposed EICR was established, and effects of geometric parameters on pump performance were discussed. The working characteristics of the EICR were analyzed and compared with the conventional claw rotor. The internal flow fields of the claw vacuum pump with the EICR were illustrated through numerical simulations, and the fluid flow variation of gas pressure inside a working chamber was analyzed. Results show that the EICR reduces carryover volume by 17.97% compared with the conventional claw rotor; meanwhile, multiple working chambers proceeding over-compression and expansion process of the conventional claw rotor are changed into one working chamber of the EICR during the mixing process. Therefore, the EICR dramatically improves the pump performance, and effectively alleviates the adverse effects of the mixing process.

Two-fluid coaxial atomization in a high-pressure environment

We study the dynamics of atomization of a liquid column by a coaxial gas flow with varying gas pressures. Specifically, we analyse how the gas density increase associated with elevated gas pressures in the ambient and co-flowing gas jet influences the liquid destabilization and breakup process, as well as the resulting droplet formation and dispersion. We present new experimental results for a coaxial liquid–gas atomizer operating in a high-pressure environment, with gas–liquid momentum ratio in the range $M = 5\unicode{x2013}56$ and pressurized gas densities $\rho _g/\rho _0 = 1\unicode{x2013}5$ , where $\rho _0$ is the ambient gas density at standard conditions. High-speed shadowgraphy images are used to quantify the spatially and temporally varying liquid–gas interface in the spray near-field. Liquid core lengths, spreading angles and other spray metrics are presented, and the influence of gas density is identified from the comparison with atomization at atmospheric conditions. In the spray mid-field, phase Doppler interferometry is used in conjunction with laser Doppler velocimetry to quantify the droplet size and velocities, as well as their radial variations across the spray. Results show an increase in droplet size at elevated ambient pressures, when keeping the gas–liquid momentum ratio constant. Finally, we show that these observations are in line with predictions from the Kelvin–Helmholtz and Rayleigh–Taylor instabilities, both of which are relevant to the gas–liquid atomization process.

Fuzzy control of a landing gear system with oleo-pneumatic shock absorber to reduce aircraft vibrations by landing impacts

PurposeThe purpose of this paper is to control a landing gear system with an oleo-pneumatic shock absorber with the fuzzy controller.Design/methodology/approachThe landing gear system with an oleo-pneumatic shock absorber is modeled mathematically. A fuzzy controller is designed for reducing aircraft vibrations. Stroke velocity and main mass velocity parameters were used to decide variable gas pressure with the fuzzy controller.FindingsThe fuzzy controller, designed according to stroke velocity and main mass velocity, reduces aircraft vibrations by the landing impacts. The controller can provide strong robustness because it shows similar good performance for different descent speeds.Research limitations/implicationsThis study was carried out through simulations in a computer environment and has not been experimentally tested in a real environment. In addition, signal and measurement delays are not taken into account. In future models, the effects of these signal delays can be added, and the controller can be tested on a real model.Originality/valueIn this study, to the best of the authors’ knowledge, for the first time, the gas pressure for the landing gear system using an oleo-pneumatic shock absorber was controlled by a fuzzy controller that adjusts the stroke velocity and the main mass velocity. Although the oleo-pneumatic shock absorber model contains high nonlinearities, the designed fuzzy controller gave successful results as robust.

A multiple sulfur record of super-large volcanic eruptions in Archaean pyrite nodules

Archaean supracrustal rocks carry a record of mass-independently fractionated S that is interpreted to be derived from UV-induced photochemical reactions in an oxygen-deficient atmosphere. Experiments with photochemical reactions of SO2 gas have provided some insight into these processes. However, reconciling experimental results with the multiple S isotopic composition of the Archaean sedimentary record has proven difficult and represents one of the outstanding issues in understanding the Archaean surface S-cycle. We present quadruple S isotope data (32S, 33S, 34S, 36S) for pyrite from Mesoarchaean carbonaceous sediments of the Dominion Group, South Africa, deposited in an acidic volcanic lake, which help reconcile observations from the Archaean sedimentary record with the results of photochemical experiments. The data, which show low Δ33S/δ34S ratios (mostly ≪ 1) and very negative Δ36S/Δ33S ratios (−4 and lower), contrast with the composition of most Archaean sedimentary sulfides and sulfates, having Δ36S/Δ33S∼−1 (the so-called ‘Archaean reference array’), but match those of modern photochemical sulfate aerosols produced in the stratosphere, following super-large volcanic eruptions, and preserved in Antarctic ice. These data are also consistent with the results of UV-irradiation experiments of SO2 gas at variable gas pressure. The S isotope composition of the Dominion Group pyrite is here interpreted to reflect the products of photolysis in a low-oxygen-level atmosphere at high SO2 pressure during large volcanic eruptions, mixed with Archaean ‘background’ (having a composition broadly similar to the Archaean reference array) S pools. It is inferred that high sedimentation rates in a terrestrial basin resulted in an instantaneously trapped input of atmospheric S during short-lasted depositional intervals, which faithfully represents transient photochemical signals in comparison with marine sedimentary records.

Understanding the influence of unsteady and convection terms in heat transfer model on the predicted heat flux in engines operated under different combustion modes

The aim of current research is to develop an enhanced heat transfer model to accurately predict the heat flux through the cylinder walls during the working process of internal combustion engines operated under different loads and combustion modes. Two enhanced models, i.e., the unsteady model and the steady convective contribution (SCC) model were respectively constructed based on the thermal wall function. The effects of the transient ambient gas temperature and pressure variations, as well as the chemical reaction source term, were included in the unsteady model. Then the contributions of the unsteady terms, such as the temporal derivative of gas temperature, the pressure work, and the chemical heat source in the energy equation were analyzed in detail. The results indicate that the mechanism of the unsteady heat transfer process is different in the engine operated under motored conditions and different combustion modes, including conventional diesel combustion (CDC), homogeneous charge compression ignition (HCCI), and reactivity controlled compression ignition (RCCI). Afterward, the influence of the gas velocity and the pressure difference perpendicular to the walls were included in the SCC model to consider their contributions to the heat fluxes near the chamber walls. It is found that the heat fluxes predicted by the SCC model are in better agreement with the experimental data, especially in the CDC mode under different swirl ratios and loads. The peak of the heat flux predicted by the SCC model shows superiority to that of the previous steady heat transfer models and the unsteady heat transfer model.

Surface Flashover Characteristics of Epoxy Resin Composites in SF6/CF4 Gas Mixture with DC Voltage

SF6/CF4 mixture is considered a potential substitution for SF6 in gas-insulated equipment owing to the considerable insulation and low temperature characteristics of CF4. This paper concerns the substitutability of the mixture on the surface flashover property. Epoxy resin composites for solid insulators are applied since flashover at the insulator interface often occurs and results in severe damage to the safe operation of the equipment. Two kinds of electrode systems are designed to study DC flashover properties with different electric field uniformities. The obtained result shows that the flashover voltage in the 20% SF6/80% CF4 mixture achieved more than 70% of the voltage in SF6 at the same pressure. The mixture shows considerable synergy in the surface flashover process and performed different tendencies with varying gas pressures and contents under different electrode systems due to the influence of surface accumulated charge. Moreover, it is considered that surface charge due to ionization may result in a reversal phenomenon for voltage polarity with increasing pressure. The results indicate the possibility of SF6/CF4 functioning as an efficient substitution of SF6 with a considerable insulation property and improved environmental protection characteristics.

Magma fracking and production reservoirs beneath and adjacent to Mutnovsky volcano based on seismic data and hydrothermal activity

Mutnovsky geothermal area in Kamchatka, Russia where 62 MWe GeoPP installed - is a source of geothermal electricity supply, as well as a hazard volcanic area. We used local seismicity micro-earthquakes (MEQ's) data from 2009 to 2021 to define seismogenic faults beneath and adjacent to Mutnovsky volcano, which interpreted as magma injections in form of dykes and sills. Magma fracking beneath Mutnovsky volcano pointed on shear mode low angle dykes in northeast sector and opening mode geomechanical conditions at -3000 m, where sills in area of 62 km2 are suggested to be formed. Low angle dykes injections were reproduced by hydromechanical simulation using CFRAC, modeling results matches with MEQ's statistics observed.Mutnovsky GeoPP steam collection system shows sensitivity to non-condensable gasses (NCG) content (partial gas pressure) variations (2019—2020), that is used as indicator of magmatic gasses recharge via magma fracking volcano system to production geothermal reservoir. Partial gas pressure measured at GeoPP condenser unit. Magma injections associated with NCG (CO2) release in production reservoirs seems to be synchronize with partial NCG pressure excursions at GeoPP condenser. Some signs of magma fracking events were also revealed using discreet observations (2016–2021) on a blowing wells on a foothills of Mutnovsky volcano. Magma fracking beneath Mutnovsky volcano is associate with small and medium hydrothermal explosions and landslide (2009–2021). Magma fracking distributions pointed on a new potentially production geothermal reservoir beneath northeast foothills of Mutnovsky volcano (depth range from -4000 to -2000 m, accessible area of 30 km2).

Analysis of the Morphology of the Growth Interface as a Function of the Gas Phase Composition during the PVT Growth of Silicon Carbide

The growth conditions of 75 mm SiC crystals in the PVT process is varied by different methods while the temperature field is kept constant. The addition of graphite into the source material leads to the formation of an ordered step flow with step heights of 0.014 µm, while the addition of graphite into the source together with N2 doping changes the step kinetics on the main facet, leading to very large, bunched steps of 0.17 µm. When elemental Si was added into the source material large macro steps are formed on the whole crystal surface. While the doping induced step bunching is related to the incorporation kinetics, the large steps induced in Si-rich conditions are attributed the reduction of surface energy. With the variation of the inert gas pressure the morphology of the surface is altered, similarly. Under low pressure conditions (0.2 mbar) a fine step structure evolves, while at a high pressure (40mbar) large surface steps are formed on the whole growth interface. Large surface steps are strongly impeded in their lateral motion at defects permeating the growth interface. At these sites the formation of foreign polytypes is facilitated.

A Numerical Study of Effect of Operating Conditions on Hydrogen Crossover Through Perforated PFSA Membrane

In this work, a three-dimensional monophasic mass transport PEMFC model has been established in order to investigate the gas pressure distribution and to quantify the hydrogen crossover through the Nafion PEM side. The model is performed using finite element approach under a commercial software platform. The effects of anodic inlet gas pressure and membrane pinhole location have been investigated. In addition, the hydrogen flow rate by permeation and the hydrogen flow rate leak across the pinhole have been estimated at different reaction rate values and pinhole sizes. The results show that the hydrogen crossover distribution is inhomogeneous. It begins with a strong increase in the inlet channel side, and ends with a large decrease in the outlet channel. The effect of variation of inlet gas pressure on hydrogen crossover is stronger in comparison with that due to the variation of pinhole size or functioning temperature, especially in case of high reaction rate. In addition, the presence of pinhole favors a slightly increase in hydrogen flow rate across the membrane at the outlet channel side.

Numerical Simulation of Erosion Wear for Continuous Elbows in Different Directions

The purpose of the present study is to simulate the continuous bend erosion process in different directions, using the dense discrete particle model (DDPM). The influence of the length of the straight pipe in the middle of the continuous bend is investigated. The Rosin–Rammler method is introduced to define the diameter distribution of erosion particles, which is theoretically closer to the actual engineering erosion situation. The numerical model is based on the Euler–Lagrange method, in which the continuous phase and the particle phase are established on a fixed Euler grid. The Lagrange model is used to track the particles, and the interaction between particles is simulated by particle flow mechanics theory. The velocity field distribution, pressure variation, and turbulent kinetic energy of gas–solid two-phase flow, composed of natural gas and gravel in the pipeline, are studied. The simulation results, using the one-way coupled DPM and the four-way coupled DDPM, are compared and analyzed. The results show that the DDPM has good accuracy in predicting the distribution of the continuous bend erosion processes in different directions. The erosion rates of particles with an average distribution size of 50 μm are significantly increased (8.32 times), compared with that of 10 μm, at the same gas transmission rate. It is also indicated that it is important to consider the impact between particles and the coupling between fluid and particles in the erosion simulation of the continuous elbow when using the CFD method.

Microstructural, Mechanical and Wear Behavior of HVOF and Cold-Sprayed High-Entropy Alloys (HEAs) Coatings

HEAs powders, unlike standard alloys which contain one or two base elements, are new alloys that contain multiple elements in the same quantity. These materials have outstanding physical and mechanical properties and for this reason, are of great interest in the material science community for their application in advanced industrial sectors. In this investigation, cold spray (CS) and high-velocity oxy fuel (HVOF) processes were used to deposit Cantor alloy (FeCoCrNiMn) coatings. Starting feedstock powders were thoroughly characterized in terms of size, shape, phase and elastic modulus. For CS process, the coating deposition efficiency and porosity could be optimized by varying gas pressure, gas temperature and stand-off distance. In the case of HVOF process, stand-off distance influenced the thickness of the coatings. Besides, on the optimized CS and HVOF coatings, corrosion tests in 3.5% NaCl solution, as well as rubber wheel, ball on disk and jet erosion tests were carried out to evaluate their wear behavior. Also, to benchmark the corrosion and wear behavior of optimized coatings, the results were compared to 316L and C-Steel bulks. The tribological study shows that Cantor alloy coatings deposited via CS and HVOF are promising to protect parts and components in a harsh environment.

Methodical selection of thermal conductivity models for porous silica-based media with variation of gas type and pressure

If the effective thermal conductivity of a silica powder in any gas atmosphere is to be calculated analytically, one is faced with a whole series of decisions. There are a lot of different models for the gas thermal conductivity in the pores, the thermal accommodation coefficient or the effective thermal conductivity itself in the literature. Furthermore, it has to be decided which input parameters should be used. This paper gives an overview and recommendations as to which calculation methods are best suited for the material classes of precipitated silica, fumed silica, silica gel and glass spheres. All combinations of the described methods result in a total of 2800 calculation models which are compared with pressure-dependent thermal conductivity measurements of 15 powdery materials with 7 different gases using Matlab computations. The results show that with a model based on a spherical unit cell, which considers local Knudsen numbers, the measuring points of all powder-gas combinations can be determined best with an average variance of about 18.5%. If the material class is known beforehand, the result can be predicted with an average accuracy of about 10% with the correspondingly determined methods.

Interaction between double nonspherical bubbles in compressible liquid under the coupling effect of ultrasound and electrostatic field

A dynamic model for a double-bubble system in compressible liquid under the coupling effect of ultrasound and electrostatic field was developed here. In this study, we mainly discussed the effect of the interaction on the investigated bubble using the numerical solutions to the theoretic model. The variable parameters are the distance between bubble centers and the initial radius of the adjacent bubble. In addition, we applied approximate equations to analyse variations of the internal gas pressure and temperature of a bubble. We found that, the oscillation amplitude of a bubble with an adjacent bubble significantly reduces, compared to that of an isolated bubble.

Gas pressure control of electric arc synthesis of composite Sn–SnO2–C nanomaterials

It was found that the variation of a buffer gas pressure in the reactor chamber can control the structure of the synthesized materials during electric arc sputtering of composite Sn–C electrodes. The gas dynamic model calculated by the direct simulation Monte Carlo method shows that the buffer gas pressure affects the local parameters of tin and carbon vapor condensation. As a result, Core-shell Sn–SnO2 nanoparticles packed in a carbon matrix with various structural properties have been synthesized. It has been found that an increase in the buffer gas pressure leads both to an increase in the average size of the synthesized nanoparticles and to the formation of a more disordered structure of carbon. In turn, the tin and carbon structure affects the electrochemical characteristics of the synthesized Sn–C composite as anode materials for lithium-ion batteries.

Influence of the growth conditions on the formation of macro-steps on the growth interface of SiC-Crystals

Several SiC crystals were grown in the same temperature field with a variation of the gas phase and the resulting step morphologies on the surface are analyzed using Laser Scanning Microscopy (LSM). It is shown that the step morphology changes due to doping, but also due to different C/Si ratios in the gas phase. By the addition of graphite into the source powder a reduction of Si-excess was achieved and an ordered step structure with an average height of 0.014 µm and width of 5.0 µm was formed. In the n-type doped case (n = 5.9∙1018 cm−3) the morphology on the facet differs strongly. Bunched steps with heights of 0.17 µm and widths of 152 µm are found. Between the diverse large macro-steps, a very ordered structure of unit cell height steps with a step spacing of 13.3 µm is found by Field Emission Scanning Electron Microscopy (FESEM) and Atomic Force Microscopy (AFM). A different change in the step morphology occurs over the whole crystal surface when elemental silicon is added into the source material. In contrast to the doping induced case, the bunched steps are more closely spaced and exhibit average heights of 0.20 µm and widths of 22 µm. The steps are noticeably retained at defects like micropipes or threading dislocations. The N2 induced step bunching is related to step kinetics on the main facet but the formation of macro-steps in the Si-rich case is assigned to the formation of stable surface steps. The variation of the inert gas pressure in the growth cell also changes the C/Si ratio in the gas phase as the diffusion from source to seed of the reactive gas species is affected differently. With a low inert gas pressure of 0.2 mbar a larger C/Si ratio in the gas phase is formed leading to steps with heights too small for analysis in the LSM, while the growth in 40 mbar promotes a smaller C/Si ratio leading to the formation of bunched steps with heights of 0.10–0.20 µm and with an average distance of 4.3 µm between them. The crystals grown in a gas phase comprising a large C/Si ratio show a better polytype stability than the crystals grown in Si-rich conditions. The instabilities can partly be attributed to the pile up of the macro-steps at defects exposing large 0001¯ terraces, where 2D-nucleation of foreign polytypes can occur.

Wireless sensor networks for pharmaceutical lyophilization: Quantification of local gas pressure and temperature in primary drying

Wireless sensor networks have become prolific in a wide range of industrial processes and offer several key advantages over their wired counterparts in terms of positioning flexibility, modularity, interconnectivity, and data routing. We demonstrate their utility in pharmaceutical lyophilization by developing a series of wireless devices to measure spatial variations in gas pressure and temperature during primary drying. The influence of shelf temperature, chamber pressure, excipient concentration, and dryer configuration are explored for various representative cycles using a laboratory-scale pharmaceutical lyophilizer. Pressure and temperature variations across the shelf for these cases are shown to vary up to 1.2 Pa and 10 °C, respectively. Experimental measurements are supported by computational fluid dynamics simulations to reveal the mechanisms driving the vapor flow. The measurements and simulation data are then combined to estimate the shelf-wise sublimation rate in the inverse sense to within a deviation of 3% based on comparison with gravimetric data. We then apply the sublimation rate profile to obtain the vial heat transfer coefficient and product mass transfer resistance for a 5% w/v mannitol formulation. Finally, these parameters are applied to a one-dimensional quasi-steady heat transfer model to predict the evolution of the product temperature over the course of primary drying. Thermocouple measurements of product temperature are compared directly to the simulated data and demonstrate accuracy comparable to existing published one-dimensional models.

Molecular Origin of Wettability Alteration of Subsurface Porous Media upon Gas Pressure Variations

Upon extraction/injection of a large quantity of gas from/into a subsurface system in shale gas production or carbon sequestration, the gas pressure varies remarkably, which may significantly change the wettability of porous media involved. Mechanistic understanding of such changes is critical for designing and optimizing a related subsurface engineering process. Using molecular dynamics simulations, we have calculated the contact angle of a water droplet on various solid surfaces (kerogen, pyrophyllite, calcite, gibbsite, and montmorillonite) as a function of CO2 or CH4 gas pressure up to 200 atm at a temperature of 300 K. The calculation reveals a complex behavior of surface wettability alteration by gas pressure variation depending on surface chemistry and structure, and molecular interactions of fluid molecules with surfaces. As the CO2 gas pressure increases, a partially hydrophilic kerogen surface becomes highly hydrophobic, while a calcite surface becomes more hydrophilic. Considering kerogen and calcite being the major components of a shale formation, we postulate that the wettability alteration of a solid surface induced by a gas pressure change may play an important role in fluid flows in shale gas production and geological carbon sequestration.