Ambient Gas Pressure Research Articles

Ion Mobility Spectrometry of Superheated Macromolecules at Electric Fields up to 500 Td.

Since its inception in 1980s, differential or field asymmetric waveform ion mobility spectrometry (FAIMS) has been implemented at or near ambient gas pressure. We recently developed FAIMS at 15-30 Torr with mass spectrometry and utilized it to analyze amino acids, isomeric peptides, and protein conformers. The separations broadly mirrored those at atmospheric pressure, save for larger proteins that (as predicted) exhibited dipole alignment at ambient but not low pressure. Here we reduce the pressure down to 4.7 Torr, allowing normalized electric fields up to 543 Td-double the maximum in prior FAIMS or IMS studies of polyatomic ions. Despite the collisional heating to ∼1000 °C at the waveform peaks, the proteins of size from ubiquitin to albumin survived intact. The dissociation of macromolecules in FAIMS appears governed by the average ion temperature over the waveform cycle, unlike the isomerization controlled by the peak temperature. The global separation trends in this "superhot" regime extend those at moderately low pressures, with distinct conformers and no alignment as theorized. Although the scaling of the compensation voltage with the field fell below cubic at lower fields, the resolving power increased and the resolution of different proteins or charge states substantially improved.

Using the Nonlinear Duffing Effect of Piezoelectric Micro-Oscillators for Wide-Range Pressure Sensing

This paper investigates the resonant behaviour of silicon-based micro-oscillators with a length of 3600 µm, a width of 1800 µm and a thickness of 10 µm over a wide range of ambient gas (N2) pressures, extending over six orders of magnitude from 10−3 mbar to 900 mbar. The oscillators are actuated piezoelectrically by a thin-film aluminium-nitride (AlN) layer, with the cantilever coverage area being varied from 33% up to 100%. The central focus is on nonlinear Duffing effects, occurring at higher oscillation amplitudes. A theoretical background is provided. All relevant parameters describing a Duffing oscillator, such as stiffness parameters for each coverage size as well as for different bending modes and more complex modes, are extracted from the experimental data. The so-called 2nd roof-tile-shaped mode showed the highest stiffness value of −97.3∙107 m−2s−2. Thus, it was chosen as being optimal for extended range pressure measurements. Interestingly, both a spring softening effect and a spring hardening effect were observed in this mode, depending on the percentage of the AlN coverage area. The Duffing-effect-induced frequency shift was found to be optimal for obtaining the highest pressure sensitivity, while the size of the hysteresis loop is also a very useful parameter because of the possibility of eliminating the temperature influences and long-term drift effects of the resonance frequency. An reasonable application-specific compromise between the sensitivity and the measurement range can be selected by adjusting the excitation voltage, offering much flexibility. This novel approach turns out to be very promising for compact, cost-effective, wide-range pressure measurements in the vacuum range.

Multi-pass probing for high-sensitivity tomographic interferometry

Optical probing is an indispensable tool in research and development. In fact, it has always been the most natural way for humankind to explore nature. However, objects consisting of transparent materials with a refractive index close to unity, such as low-density gas jets, are a typical example of samples that often reach the sensitivity limits of optical probing techniques. We introduce an advanced optical probing method employing multiple passes of the probe through the object to increase phase sensitivity, and relay-imaging of the object between individual passes to preserve spatial resolution. An interferometer with four-passes was set up and the concept was validated by tomographic characterization of low-density supersonic gas jets. The results show an evident increase of sensitivity, which allows for the accurate quantitation of fine features such as a shock formed by an obstacle or a barrel shock on the jet boundary in low ambient gas pressures. Despite its limitations in temporal resolution, this novel method has demonstrated an increase in phase sensitivity in transmission, however, it can also be employed to boost the absorption or polarization contrast of weakly interacting objects in both transmission and reflection setups, thus, upgrading the sensitivity of various optical characterization methods.

Highly conductive graphite matrix/copper composites by a pressureless infiltration method

Graphite matrix/copper composites have found significant potential uses in numerous areas. Until now, a high ambient gas pressure has to be applied to overcome the non-wettability between the copper melt and graphite matrix, which has restricted the technological and economic efficiencies, as well as the composite performance. In this paper, we have proposed a pressureless infiltration strategy to realize the preparation of highly conductive graphite matrix/copper composites. A tungsten carbide network is first in situ constructed in the graphite matrix, transforming the capillary force from the resistance mode to the impetus mode. Results show that the contact angle of graphite/copper decreased from 138.5° to 23° due to the constructed tungsten carbide network. The composites exhibit good interfacial bonding, and the electrical conductivity reaches 15.1 × 105 S/m, far higher than the requirement of the industry standard.

Comparison of the expansion behavior of atoms and droplets ablated from a β-tricalcium phosphate target under low-pressure ambient H2O gas for hydroxyapatite coating

Visualizing the expansion of particles of different size in a laser-ablated plume is useful for understanding the mechanism of the pulsed-laser deposition process. In our previous work that the crystalline hydroxyapatite content in a coating layer decreased with increasing H2O gas pressure. We concluded that ablated atoms and ions, which were immediately changed into crystalline hydroxyapatite, were stopped before reaching the substrate in the H2O pressure range. In the present study, the expansion behavior of ablated droplets and atoms in H2O gas was measured independently. Droplets were also measured via Mie scattering images using a second probe laser beam and were found to not be affected by the ambient gas pressure. However, the excited Ca atoms and ions in this H2O pressure range were effectively prevented from reaching the substrate. These confirm that the decrease in the crystalline hydroxyapatite content was caused by the increase in the ambient gas pressure.

Effect of ambient pressure on gas adsorption characteristics of residual coal in abandoned underground coal mines

To study the influence of ambient pressure on gas adsorption of residual coal and provide a basis for establishing a reasonable calculation model of gas resource adsorbed in residual coal in abandoned underground coal mines, the residual coal was divided into loose-type residual coal and column-type residual coal after an analysis on the ambient gas pressure variation process. Then the gas adsorption experiments were conducted under adsorption equilibrium pressure range of 0.5–2.5 MPa using a self-made experimental device. The results show that (1) In the range of 0.5–2.5 MPa, the amount of methane adsorption in the loose-type residual coal under the intense replenishment condition can be 19.5% less than that under the gradual replenishment condition. (2) With a continuous decrease in ambient pressure, the methane adsorption amount in the column-type coal is reduced. The adsorption capacity at a unit pressure drop gradually increases from a minimum of 0.24 mL▪g-1 × 0.1 MPa−1 to a maximum of 2.375 mL▪g-1× 0.1 MPa−1. The initial adsorption equilibrium pressure shows little effect on the methane adsorption in column-type residual coal. (3) The bigger difference of the methane adsorption amount, with a maximum of 2.347 mL▪g-1, between the loose-type residual coal and column-type residual coal under the intense replenishment condition can be observed in the pressure range of 0.8–1.2 MPa. Therefore, the coal type should be considered to establish a gas storage model of residual coal in abandoned coal mines.

Microscopic spray measurements of non-reacting alternative jet fuel: Effect of ambient gas temperature

The volatile characteristics of alternative Gas-to-Liquid (GTL) jet fuel and conventional Jet A-1 fuel are significantly different due to their chemical composition variations. This difference can have a strong influence on the atomization performance at elevated ambient gas temperature conditions. Because the atomization process plays a vital role in fuel distribution inside the combustor, which ultimately affects heat release and emission patterns. The objective of the present work is to investigate the effects of ambient gas temperature and nozzle pressure differential on the non-reacting, microscopic spray performance of the alternative jet fuel using a pressure-swirl nozzle, and then, compare these effects to those of Jet A-1 fuel. Specifically, this study investigates the droplet size, velocity and distribution, by employing the Phase Doppler Anemometry technique to measure these parameters at several radial and axial locations downstream of the nozzle exit. The effect of ambient gas temperatures is studied at 300, 350, and 400 K at two nozzle pressure differentials, 300 and 900 kPa, while maintaining a constant ambient gas pressure and fuel temperature. Results show that, in the region investigated, there is a significant difference between the spray performances of GTL and Jet A-1 at elevated operating conditions. The outcomes of this study will add new knowledge to the limited scientific literature on the effect of ambient gas conditions on the local spray parameters of alternative jet fuel.

Modelling of Input Parameters for Power Generation using Regression Models

In this study, multiple linear regression models were employed in the correlation of gas supply and power generation using a gas Power Plant in Niger Delta, Nigeria as a Case study. From the analysis based on outlier detection, reliability analysis and test of homogeneity, it was observed that the independent variable data such as ambient temperature, gas pressure and compressed temperature failed normality test. Therefore, the use of any linear model for either analysis or modelling of the data was not acceptable. Data used for reliability analysis of the gas pressure and compressed temperature difference were positively correlated with power generation, having a covariance value of 0.639 and 113.148. The ambient temperature was negatively correlated with power generation, having a covariance value of 14.564. The positive value showed that both dimensions exclusively increased and decreased together with respect to the output while the negative value showed that increment in value of one variable led to decrease in the value of the other, and vice versa.

Growth and Morphology of Water-, Methanol-, and Ethanol-ice Dust Grains Formed in an Astrophysically Relevant Plasma Experiment

Abstract Ice dust grains composed of water, methanol, and ethanol are successfully produced in a laboratory plasma experiment operating at astrophysically relevant temperatures. Both methanol- and ethanol-ice grains grow in an elongated and branched way similar to water-ice grains formed in a plasma. The experiment reveals that methanol- and ethanol-ice grains grow faster, larger, and more branched (spikier) than water-ice grains. The observed growth features seem to be related to the fact that more source molecules and monomer grains can exist in the system at the same temperature. The observed morphology is in agreement with the characteristics of the diffusion-limited aggregation. We also find that larger and more branched ice grains form when the ambient gas pressure is low or the mass of the ambient gas is light, indicating that the aggregation of small grains is enhanced under these conditions.

Aqueous mineral carbonation of oil shale mine waste (limestone): A feasibility study to develop a CO2 capture sorbent

The development of a Ca-based CO2 capture sorbent from a limestone-rich mine waste via aqueous mineral carbonation was first time evaluated. Aqueous carbonation of calcined oil shale mine waste rock was conducted at the laboratory scale at ambient temperature and atmospheric gas pressure using CO2 gas mixture simulated the average exhaust gas composition of a fossil fuel power generation plant. The dissolution and carbonation of calcium were found to be optimal at 2.5% pulp density and were found to proceed faster during the initial 5–10 min. The overall aqueous carbonation efficiency was estimated at ≥89%. The carbonation process resulted in the production of pure calcite, whereas a mixture of Ca and Mg carbonates was found in the reaction residue. The CO2 uptake capacity (∼80 wt%) of the developed Ca-based sorbent was promising and revealed that it can be used for direct CO2 capture.

Mathematical modeling of electric consumption of the gas cooling process

In the article, the possibility of determining the consumption of electrical energy by gas air cooling devices. Special attention is paid to the processing of experimental results. There are some assumptions in the mathematical model that do not affect the final result. The factors influencing the consumption of electric energy by gas air coolers are given. It is stated that the ambient temperature and gas pressure significantly affect the consumption of electrical energy. Thus, based on experimental data, a model of electrical energy consumption by gas air cooling devices of main compressor stations has been obtained.

Numerical study of the effect of atomic mass of the ambient gas on the expansion and the lateral interactions of LBO plumes

The characteristics of the lateral interaction of two LBO plasma plumes in argon Ar ambient gas at high pressures were reported in a recent publication (Yadav et al 2017 J. Phys. D: Appl. Phys. 50 355201). Further, we have investigated the interaction characteristics of plumes in He, Ne, Ar and Xe gases to see the effect of atomic mass on the interaction. The present work illustrates the applicability of the present model for theoretical understanding of dynamics, structure, density variation, shock wave formations and their interactions of two propagating plasma plumes in a wide range of ambient conditions. The formation of interaction region, geometrical shape and strength of the shock fronts and subsequent regular and Mach reflections in accordance with the nature and pressure of ambient gas are successfully captured in the simulations.

Effects of donor density on power-law response in tin dioxide gas sensors

We investigated the power-law responses in two types of tin dioxide (SnO2) films: one made from nanosized grains and another from from very large grains, both under dry air. Experimental results revealed a significant dependence between the sensitivity and the SnO2 grain size. We therefore propose, that the gas sensor sensitivity is not only determined by oxygen chemisorption, but also by changes in the density of oxygen vacancies in response to changes in the ambient gas pressure. Band bendings and adsorbate coverages for different oxygen pressures were derived resorting to the electroneutrality condition, including changes in the concentration of oxygen vacancies within the grains due to the exposure to different oxygen pressure. The consequences for the film conductivity and its power-law response were analyzed and compared with experimental results.

Creating Strong Titanium/Titanium Hydride Brown Bodies at Ambient Pressure and Moderate Temperatures.

A simple, low temperature, method, hydrogen-enhanced atomic transport (HEAT), for creating metallic-bonded brown bodies of order 40% bulk density in molds of designed shape from Ti metal particles is introduced. In this initial study 40 micron titanium particles were poured into graphite molds, then heated to temperatures equal to or greater than 650 °C for four hours in a flowing ambient pressure gas mixture containing some hydrogen led to brown body formation that closely mimicked the mold shape. The brown bodies were shown to be dense, metallic bonded, and consisted of primarily Ti metal, but also some TiH. It is postulated that hydrogen is key to the sintering mechanism: it enables the formation of short-lived TiHx species, volatile at the temperatures employed, that lead to sintering via an Ostwald Ripening mechanism. Data consistent with this postulate include findings that brown bodies are formed with hydrogen present (HEAT process) had mechanical robustness and only suffered plastic deformation at high pressure (ca. 5000 Atm). In contrast, brown bodies made in identical conditions, except the flowing gas did not contain hydrogen, were brittle, and broke into micron scale particles under much lower pressure. HEAT appears to have advantages relative to existing titanium metal part manufacturing methods such as powder injection molding that require many more steps, particularly debinding, and other methods, such as laser sintering, that are slower, require very expensive hardware and expert operation.

Investigation of Self-Heating Effects in Vacuum Gate Dielectric Gate-all-Around Vertically Stacked Silicon Nanowire Field Effect Transistors

The self-heating effects in vacuum gate dielectric gate-all-around field effect transistors (GAA FETs) with vertically stacked 4-nm silicon nanowire (SiNW) channels are investigated by 3-D TCAD simulation. The cross-sectional dimension-dependent thermal conductivity model of the SiNW is proposed for the precise numerical simulation of self-heating effects based on the temperature-dependent thermal conductivity of the bulk silicon. The thermal conductivity model which was verified by published data indicates that thermal conductivity of 4-nm SiNW is greatly reduced to below 10 W/mK due to the pronounced phonon boundary scattering. Simulation results shows that the vacuum gate dielectric devices undergo more severe self-heating effects than the solid gate dielectric GAA SiNW FETs, resulting in more serious performance degradation. Multiple heat sources generated by the three-stacked SiNWs make heat generation and diffusion more difficult. An effective method is proposed to suppress the self-heating effects by increasing the spacing of the gas gap within in a certain range and the around ambient gas pressure.

Entrainment flow of a jet emerging into a half-space with the no-slip boundary condition

The current development of micro-scale technologies increases the interest in viscous flows with low and moderate Reynolds numbers. This work theoretically studies the entrainment flow of a viscous jet emerging from a plane wall into a half-space with the objective to understand the conditions where a similarity model can approximate a realistic flow. Two similarity models having analytic solutions are considered: the flow dominated by the momentum flux and the flow dominated by the mass flux. Algorithms are proposed to evaluate the parameters of the similarity models from the mass and momentum balances. Distributions of flow parameters and stresses on the wall are calculated for the similarity models. They are compared with the corresponding distributions obtained by computational fluid dynamics for a more realistic model with a finite size of the jet source and competitive influence of the mass and momentum fluxes. This comparison validates the mass-dominated similarity model at the jet Reynolds number Re ≤ 10 and the momentum-dominated similarity model at Re ≥ 30. The obtained results are applied to the problem of laser evaporation in selective laser melting. It is shown that the theoretically estimated flow velocity corresponds to the experimentally observed one. The theory explains the formation of the experimentally observed denuded zone and its widening by decreasing the ambient gas pressure.

Truncation of a nanosecond CO2 laser pulse by following of the temporal characteristics of the plasma parameters in laser ablation model

The evolution of laser-induced plasma for an aluminum target in a helium ambient gas at different pressures of 100, 300, 500, 700, and 1000 mbar is numerically studied. A thermal model of laser ablation is utilized for calculation of plasma parameters which comprise heat conduction, Euler equations, Saha–Eggert equations, Knudsen layer boundary condition, mass and energy balance relations, and optical shielding effects. In addition, in order to determine the temporal parameters of aluminum's plasma, the hydrodynamic equations are computed for calculation of the plasma absorption due to inverse Bremsstrahlung and photoionization. A CO2 laser pulse at a wavelength of 10.6 μm with different pulse durations of 50 and 100 ns is irradiated on laser induced Al plasma for truncation of the transmitted CO2 laser pulse. The laser intensities irradiated on the Al sample for producing plasma and generation of a shortened pulse are considered as 1016, 1017, and 5 × 1017 W/m2. Furthermore, for validation of the theoretical calculations, some experimental results are presented. Results showed that higher helium gas pressures caused the critical density attained at earlier delay times which caused the CO2 laser beam became efficiently truncated. Moreover, it is concluded that pulse duration has an inverse relation with ambient gas pressure and laser intensity which means that the higher gas pressure or laser intensity induces less pulse duration.

Effect of Ar Gas Pressure on LSPR Property of Au Nanoparticles: Comparison of Experimental and Theoretical Studies.

In this study, the thin films were produced by using pulsed laser deposition (PLD) technique from gold (Au) nanoparticles deposited on two kinds of substrates under different argon (Ar) gas pressure. Microscope glass slides and silicon (100) wafers were used as amorphous and crystal substrates. The films were deposited under 2 × 10−3 mbar, 1 × 10−2 mbar, 2 × 10−2 mbar argon (Ar) ambient gas pressure. Effect of the background gas pressure on the plasma plume of the ablated Au nanoparticles was investigated in details. Morphology of Au nanoparticle thin films was investigated by means of atomic force microscopy (AFM) technique. Absorption spectra of Au nanoparticles were examined by using UV-Vis spectrometry. Extinction spectra of Au nanoparticles were calculated by using metallic nano particles boundary element method (MNPBEM) simulation programme. Both experimental spectra and simulation data for Au nanoparticles were obtained and compared in this work. It was concluded that they are also in good agreement with literature data. The measurements and the simulation results showed that localized surface plasmon resonance (LSPR) peaks for Au nanoparticles were located in the near infrared region (NIR) because of the larger size of the disk-like shape of Au nanoparticles, and the near-field coupling between Au nanoparticles. It was demonstrated that as the ambient gas (Ar) pressure was increased, the size and the density of Au nanoparticles on the substrate were decreased and the LSPR peak shifts toward the short wavelength region in the spectrum. This shift has been explained by the changes in the morphology of produced thin films.

Impacts of duct inner diameter and standoff distance on macroscopic spray characteristics of ducted fuel injection under non-vaporizing conditions

Ducted fuel injection spray is a new technology for reducing soot formation in heavy-duty diesel engines. In this work, the ducted fuel injection spray characteristics with different duct inner diameters and different standoff distances were investigated and compared with free spray. Duct inner diameter ranged from 1.5 to 4 mm, and standoff distance varied between 0.9 and 4.9 mm. Mie-scattering optical technique was used to characterize spray characteristics under various injection pressures in a constant-volume spray chamber. Ambient gas pressure of up to 6 MPa when spraying. The results showed that ducted fuel injection spray with smaller duct has better spray diffusion compared to those of ducted fuel injection sprays with larger ducts and free spray from the perspectives of spray tip penetration, spray cone angle and spray area. Increasing standoff distance could increase spray velocity. Ducted fuel injection spray with smaller duct formed a mushroom-shaped head and large-scale vortex flow close to the duct outlet. All the advantages of ducted fuel injection spray with smaller duct are interpreted as evidence of improving fuel–gas mixing quality significantly.

Numerical Investigation of the Influence of Oil Dilution on the Ability to Initiate a Pre-Ignition Combustion

<div class="section abstract"><div class="htmlview paragraph">Although the root-cause of the initial pre-ignition is not yet proven, there is a general agreement throughout the literature that it is very likely a 2-phase particle or droplet induced phenomenon. In the case of a droplet induced mechanism there are still uncertainties regarding the detached droplet size, velocity and composition. Former research work suggests that heavy wall wetting during injection is increasing the PI-frequency in WOT operation points. Due to the oil dilution the viscosity and the surface tension are reduced, which enhances the likelihood of detachment.</div><div class="htmlview paragraph">The present work is therefore investigating the influence of the oil dilution on the droplet evaporation and the PI-tendency. According to previous work performed at the research group, there is an influence of the radical ketohydroperoxide that has its origin in incomplete oil combustion on the pre-ignition probability of an engine cycle. This underlines the role of oil combustion chemistry and the oil mass fraction in detached droplets.</div><div class="htmlview paragraph">In order to characterize the droplet evaporation a multicomponent surrogate model was chosen. The selection of the species is based on the distillation curves and the basic chemical composition using a detailed distillation model. In order to capture mixture effects, the vapor-liquid-equilibrium incorporates activity coefficients calculated by the UNIFAC method. The investigated lubricant oil is modelled as a mixture of four n-alkanes based on a GC-analysis. This established model shows a good agreement with the measurement data.</div><div class="htmlview paragraph">The fluid surrogates are transferred to a CFD-code to predict the evaporation behavior of different oil-fuel mixtures under engine-like conditions. Different release timings during a compression stroke are investigated. The compression is modelled through a time-dependent change of the ambient gas pressure and temperature. Furthermore, a sensitivity analysis of the boundary conditions (D<sub>Drop</sub>, T<sub>Drop</sub>) was performed. It can be shown that a 250 μm droplet can lead to an ignitable condition up to a fuel share of 25 %.</div></div>