Influence Of Pressure Variations Research Articles

Numerical study on decomposition characteristics of natural gas hydrate based on molecular dynamics method

The molecular dynamics method is used to investigate decomposition characteristics of natural gas hydrate under different pressure and salinity. In this paper, the influence of pressure variation on the stability of natural gas hydrate under high pressure is studied from the molecular point of view based on the seabed pressure in Shenhu sea area. At the same time, taking the real marine conditions in the South China Sea as a reference, the effect of the synergistic effect of various salt ions on the decomposition of natural gas hydrate under the effect of salinity is studied. Its decomposition behavior is discussed by analyzing the parameters such as cell conformation, radial distribution function, mean square displacement and self-diffusion coefficient. The results show that pressure and salinity influence the decomposition of natural gas hydrate through modifying stable its conditions, from solid state to gas-liquid state. And the reduction of pressure accelerates the decomposition of natural gas hydrate under high pressure, while the increase of salinity promotes the decomposition of natural gas hydrate under the condition of high salinity.

How angular-momentum flux controls Francis turbine full-load surge

Hydropower plants equipped with Francis turbines may enter unstable conditions at high turbine discharge [13], with strong pulsations of power output and internal pressure. The cause are oscillations of a vapor-filled cavity in the vortex flow downstream of the turbine runner, interacting with the draft tube and penstock pressure. The paper describes the structure and simulation results of a 1D distributed-parameter model for full-load surge, parametrized from results of a high-resolution unsteady two-phase CFD simulation study (Wack [14]) of high-load pulsations in the reduced-scale model of a medium-specific speed Francis turbine. In earlier research on the same model turbine, Müller [12] had suggested that runner blade cavitation could cause instability. To clarify this, variation of turbine intake flow was sup-pressed, and the influence of pressure variation via runner blade cavitation on the relative runner exit flow angle and angular-momentum flux was simulated. Due to the upstream boundary condition, the influence of mass-flow gain χ is replaced by a cavitation gain factor ψ, likewise delayed by the limited speed of swirl propagation. It is found that gain factors obtained from steady-state simulation cannot be directly used with a lumped-parameter model because the swirl effect is much reduced due to its phase changes along the vortex; using the steady-state gain factors would thus exaggerate the influence of swirl on cavity volume. Simulation in frequency domain with realistic swirl transport delay confirms that instability can occur because in some parts of the cavitation zone the swirl provides oscillation power.

KOMPOR EKONOMIS BERBAHAN BAKAR OLI BEKAS

This study aims to determine the design of a stove (burner) fueled by used oil, along with its specifications and to find out the test results using a stove (burner) burning used oil. Departing from the lack of utilization of used oil waste and the absence of good tools to utilize used oil. On the other hand, when used as fuel, used oil does not produce complete combustion. This study uses the French design model. This study concluded that the designed stove (burner) has a large shape compared to the burner in general. The stove (burner) reaches a pressure of 3.5 bar with a temperature of 1127 °C. The flames produced by used oil are orange. Comparison of fuel results in data that LPG is 16 minutes faster than used oil in aluminum smelting. The highest flame length is 1.57 m at a variation of 3 bar air pressure and the lowest is 0.83 m at a pressure of 1 bar. There is an influence of pressure variations on the combustion temperature with a minimum and maximum temperature reaching the highest point with a pressure of 2.5 bar with a temperature of 118 °C and 994 °C while the lowest point is at a minimum and maximum temperature at a pressure of 1 bar with a temperature of 80.4 ° C and 662 °C at 0.5 bar pressure. Fuel consumption time with a distance variation of 2200 km produces a fairly short time of 12 minutes 25 seconds. While the consumption time obtained from the variation of the distance of 1800 km is 17 minutes 11 seconds.

Geometric nonlinear vibrations of rotating variable thickness plates induced by periodic incoming wakes

Incoming wakes significantly affect vibration characteristics of rotating blades in turbomachines. This paper develops a periodic incoming wake mathematical model to consider the influence of pressure variations. Considering thickness variations along both the chord to reduce vibrations and the span to decrease centrifugal stress, a wake-induced vibration model based on rotating large deformation cantilever plates is established. Natural frequencies calculated by different methods show that the present method has a high degree of accuracy. And analysis of incoming wake-induced vibrations indicates the incoming wake model can analyze effects of important parameters of such wakes on vibration characteristics. With the aggravation of wakes induced-vibrations, geometric nonlinear vibrations become more remarkable, which indicates the necessity of large deflection analysis. Discussions on variable thickness demonstrate that increasing thickness on the fixed end or maximum thickness along the chord not only reduces vibrations caused by incoming wakes, but also decreases the centrifugal stress, which are two better ways to reduce this kind of vibrations.

Quantification of atomic hydrogen anion density in a permanent magnet based helicon ion source (HELEN) by using pulsed ring down spectroscopy.

In the present work, a permanent magnet-based helicon plasma source (HELEN) is characterized as a negative ion source. A noninvasive diagnostic technique based on cavity ring down spectroscopy (CRDS) is developed to measure the line-integrated negative hydrogen ion (H-) density in HELEN. This paper discusses the experimental results in which negative hydrogen ion density is measured for different magnetic field, pressure, and RF (13.56 MHz) power configurations. It is observed that in high power range (800-850 W), the source is operating in helicon wave heating mode with a background plasma density of ∼1018 m-3 and electron temperature of ∼2 eV. Negative hydrogen ion density is measured by CRDS method and also by optical emission spectroscopic technique. The measured negative ion density is in the range of ∼1016 m-3 under volume mode operational condition even without any use of standard magnetic filter or cesium seeding in the downstream region. The influence of pressure variation (pressure range from 4 × 10-3 mbar to 4 × 10-2 mbar) on negative ion density production is not significant, except for a particular axial magnetic field configuration (55 G) and at 8 × 10-3 mbar pressure, where ∼34% hike is observed.

Analysis of elastic velocities behavior and porosity in carbonates submitted to external pressure variation

Carbonate rocks usually present a complex porous system that exhibits different behavior of porosity and elastic velocities when submitted to external pressure variation. This work aims to study compressional- and shear-wave velocity variation and porosity in carbonate rock samples submitted to external pressure variation. By analyzing the data set, it is intended to characterize carbonate rocks samples porous system. Experimental tests were carried out at the Rock Physics Laboratory of UENF/LENEP on a set of carbonate rocks. Those tests consisted of measurements of petrophysical properties, mineral composition and optical microscopy images that aid to characterize the pore system of such rocks. The Differential Effective Medium (DEM) theory was used to estimate the microporosity aspect ratio supposing a dual porosity scenario,macro-meso pores captured by optical microscopy and micropores that are out of the resolution of the image analysis. The influence of pressure variation in the aspect ratio was also studied as well as its impact on the behavior of porosity and elastic velocities for different rock textures.

Experimental Study on the Effects of Stress Variations on the Permeability of Feldspar-Quartz Sandstone

The multistage and discontinuous nature of the injection process used in the geological storage of CO2 causes reservoirs to experience repeated loading and unloading. The reservoir permeability changes caused by this phenomenon directly impact the CO2 injection process and the process of CO2 migration in the reservoirs. Through laboratory experiments, variations in the permeability of sandstone in the Liujiagou formation of the Ordos CO2 capture and storage (CCS) demonstration project were analyzed using cyclic variations in injection pressure and confining pressure and multistage loading and unloading. The variation in the micropore structure and its influence on the permeability were analyzed based on micropore structure tests. In addition, the effects of multiple stress changes on the permeability of the same type of rock with different clay minerals content were also analyzed. More attention should be devoted to the influence of pressure variations on permeability in evaluations of storage potential and studies of CO2 migration in reservoirs in CCS engineering.

Seasonal emanation of radon at Ghuttu, northwest Himalaya: Differentiation of atmospheric temperature and pressure influences

Continuous monitoring of radon along with meteorological parameters has been carried out in a seismically active area of Garhwal region, northwest Himalaya, within the frame work of earthquake precursory research. Radon measurements are carried out by using a gamma ray detector installed in the air column at a depth of 10m in a 68m deep borehole. The analysis of long time series for 2006–2012 shows strong seasonal variability masked by diurnal and multi-day variations. Isolation of a seasonal cycle by minimising short-time by 31 day running average shows a strong seasonal variation with unambiguous dependence on atmospheric temperature and pressure. The seasonal characteristics of radon concentrations are positively correlated to atmospheric temperature (R=0.95) and negatively correlated to atmospheric pressure (R=−0.82). The temperature and pressure variation in their annual progressions are negatively correlated. The calculations of partial correlation coefficient permit us to conclude that atmospheric temperature plays a dominant role in controlling the variability of radon in borehole, 71% of the variability in radon arises from the variation in atmospheric temperature and about 6% of the variability is contributed by atmospheric pressure. The influence of pressure variations in an annual cycle appears to be a pseudo-effect, resulting from the negative correlation between temperature and pressure variations. Incorporation of these results explains the varying and even contradictory claims regarding the influence of the pressure variability on radon changes in the published literature. Temperature dependence, facilitated by the temperature gradient in the borehole, controls the transportation of radon from the deep interior to the surface.

The latent fingerprint in mass transport of polycrystalline materials

Herein, a systematic investigation was carried out to reach a rational understanding and to provide information concerning the possible causes for a significant influence of pressure variation in the underlying processes of mass transport in polycrystalline materials. The authors focused their research in solid-state diffusion, a part of the subject “Mass Transport in Solids”. Theories on diffusion are the subject by itself which exists as a latent fingerprint in every text of higher learning in interdisciplinary science. In this research, authors prepared sandwich samples of titanium alloy and stainless steel using nickel as an intermediate metal. The samples were processed at three different levels of bonding pressure (3, 4 and 5 MPa) while bonding temperature and bonding time was maintained at 750 °C and 1 h, respectively, throughout the experiments. It was observed that the net flux of atomic diffusion of nickel atoms into Ti-alloy at TiA/Ni interface increased by ~63 % with the rise in the bonding pressure from 3 to 4 MPa, but decreased by ~40 % with the rise in the bonding pressure from 4 to 5 MPa. At the same time, the net flux of atomic diffusion of nickel atoms into stainless steel at Ni/SS interface increased by ~19 % with the rise in the bonding pressure from 3 to 4 MPa, but increased by ~17 % with the rise in the bonding pressure from 4 to 5 MPa. Here authors showed that the pressure variations have different effects at the TiA/Ni interface and Ni/SS interface, and tried to explain the explicit mechanisms operating behind them. In general for sandwich samples processed irrespective of bonding pressure chosen, the net flux of Ni-atoms diffused into SS is greater than that of the net flux of Ni-atoms diffused in Ti-alloy matrix by four orders of magnitude. The calculated diffusivity of Ni-atoms into Ti-alloy reaches its highest value of ~5.083 × 10−19 m2/s for the sandwich sample processed using 4-MPa bonding-pressure, whereas the diffusivity of Ni-atoms into SS reaches its peak value of ~1.615 × 10−14 m2/s for the sample bonded using 5-MPa bonding-pressure.

Estudio Numérico del Efecto de la Presión en el Proceso de Mezcla Metano-Oxígeno en un Arreglo de Chorros 4-Lug Bolt

Numerical results of methane-oxygen mixing process in a contained 4-Lug-Bolt jets array system under the influence of pressure variation are presented. The analysis was divided in two stages, low and high pressure, under the flammability limits criteria. At low pressures the density was modeled with the ideal-gas equation and for high pressures with the Redlich-Kwong equation. The predictions show that the gas mixture is highly influenced by recirculation between oxygen and methane jets, as well as a dragging effect of oxygen over the methane jet. Moreover, the pressure has no influence on the lower flammability limit, whereas it does affect the upper flammability limit. Despite these effects on flammability limits, the pressure shows no significant effect on the mixing of methane-oxygen by diffusion.

Battery thermal management by boiling heat-transfer

In this study, the ability of a boiling process to thermally condition (homogenisation and cooling) batteries is investigated. Thereto, a series of experiments are performed and discussed. Subjects that are treated are the dielectric property of the proposed cooling fluid, its cooling capability compared to that of air, the ability of the boiling fluid to thermally homogenise a battery and the influence of pressure variation on the boiling process. It turns out that the proposed cooling fluid conducts no electricity, has good cooling characteristics compared to those of air and, when boiling, is able to thermally homogenise the battery. Furthermore, pressure variation seems to offer a good method to regulate the boiling process.

Measuring pressures in a slender cylindrical silo for storing maize. Filling, static state and discharge with different material flow rates and comparison with Eurocode 1 part 4

In this paper, we report the results for pressures in full-size silos obtained from assays performed on a test station. This basically consisted of a mid-scale cylindrical silo equipped with load cells, with which it was possible to obtain most of the parameters used in the various theoretical calculation models and in existing regulations.Three different types of assay were conducted by varying the mode of silo discharge. In the first kind of assay, the silo was completely emptied following a period during which the stored material remained static. In the second type, a small amount of material was unloaded before interrupting the discharge, and in the third type, discharge was effected in several stages. We also studied the influence of variations in pressure on discharge speed.This study shows that variation in the discharge flow rate is not associated with a further increase in pressures and that the state of overpressure attained during discharge is essentially due to compaction or an increase in the specific weight of the material in given areas of the silo. We also observed that the discharge of a small amount of material caused a variation in pressures of the same magnitude as a complete discharge, and that previous pressure levels were not recovered once a partial discharge had been halted. The results of this study are compared with the Eurocode 1, part 4; in all cases, the values obtained were lower than those proposed in the Eurocode.

Combustion of Laminar Non-Premixed Acetylene Jet at Two Different Altitudes

In this article, the influence of pressure variation due to altitude change on flames is studied. A series of largely buoyancy-driven acetylene jet fire experiments was conducted at two places in China, namely Lhasa and Hefei, with altitudes of 3658 m and 50 m, respectively. A range of parameters, including flame height, flame and plume centerline temperatures, transmittance through smoke, and irradiance were measured and compared. The flame height at low altitude is higher than that at high altitude. The centerline temperatures of the flame and plume regions exhibit opposite variations with pressure. The soot mass concentration resolved by transmittance measurement follows a weaker power-law dependence on pressure under substandard atmospheric pressure than under pressure greater than standard atmospheric pressure. The radiation heat flux produced from flames of the same burning rate displays a positive proportionality to pressure.

Microstructural Analysis and Tensile Properties of Squeeze Cast Al-7%Mg Alloy

Squeeze casting is one of the modern casting processes, which was invented to address these shortcomings and has a high potential to produce sound casting alloys. Magnesium Alloys are the lightest structural alloys commercially available and have great potential for applications in aerospace and automobile industries. In this article, the influence of pressure variation on the microstructure and defects formation in the Al-7%Mg alloy during squeeze casting process was studied. It was observed that a small external pressure of 20 MPa promoted structural refinement and a significant increasing in the ultimate tensile strength. This improvement in structure and properties is attributed to increasing in the cooling rate during squeezing.

Operating Pressure Sensitivity of DistillationControl Structure Consequences

The influence of pressure variations upon distillation operation does not seem to be well-understood in the open literature, because contradicting statements concerning the importance of pressure control on binary distillation are found. To minimize energy consumption, it is recommended to operate columns at minimum pressure; however, even if column pressure is controlled, instability may still occur when both product purities are controlled in a decentralized control structure. In this paper, operating pressure sensitivity is classified according to the pressure sensitivity of the vapor−liquid equilibrium (VLE) relationship for the mixture being separated. Operating pressure sensitivity is shown to become significant at high internal flow rates. It is furthermore shown that this sensitivity may lead to a situation where different values of the internal flow rate may produce the same product purity, which commonly is labeled “input multiplicity” of the separation. This input multiplicity is shown to occur...

2609 マイクロバブルの安定性に及ぼす圧力変動の影響(S44-1 マイクロ気泡・粒子,S44 マイクロ・ナノフルイディクス)

2609 マイクロバブルの安定性に及ぼす圧力変動の影響(S44-1 マイクロ気泡・粒子,S44 マイクロ・ナノフルイディクス)

Influence of pressure variations on the formation and development of mesophase in a petroleum residue

The objective of this study is to search for a method, involving control over the pressures within a pyrolyzing system, to produce non-coalesced mesophase spheres of required sizes. Semicokes were studied from pyrolyses of a petroleum residue, R1, carried out in a tube reactor, 440–445°C, 1.0 MPa pressure, and soak times 1.0–2.0 h. In some pyrolyses, pressures were reduced from 1.0 to 0.1 MPa and the pyrolysis continued at the same reaction temperature at 0.1 MPa. These experiments are termed depressurizations. Semicokes were examined by optical microscopy to measure mesophase content as well as distributions of size of mesophase spherules and sphere concentration (number of spheres mm−2). High-pressure (1.0 MPa) pyrolyses favour the coalescence of mesophase spheres to form bulk mesophase. Initially formed spheres do not grow beyond a certain size indicating that rates of coalescence exceed rates of growth of the spheres. Depressurization causes a loss of volatile matter with a proposed resultant increase in viscosity of the remaining isotropic phase. Some volatile material may also be removed from the mesophase spheres themselves, again promoting a viscosity increase. As a result of this, the spheres increase their diameter and there is less production of bulk mesophase. With depressurization, coalescence is not stopped entirely but is reduced considerably in extent.

The Influence of Pressure Variations on the Impedance of the Human Ear Drum

The Influence of Pressure Variations on the Impedance of the Human Ear Drum