Showing papers on "Atmospheric pressure published in 2019"

Photocatalytic CO2 Conversion of M0.33WO3 Directly from the Air with High Selectivity: Insight into Full Spectrum-Induced Reaction Mechanism.

Abstract: Natural photosynthesis is a solar light-driven process utilized by plants to convert CO2 and water into carbohydrate molecules. The goal of artificial photosynthesis is the reduction of CO2 directly from air into high purity value-added products at atmospheric pressure. However, its realization, combined with deep mechanism investigation, is a huge challenge. Herein, we demonstrate that hexagonal tungsten bronze M0.33WO3 (M = K, Rb, Cs) series with {010} facets, prepared by a peculiar “water-controllable releasing” solvothermal method, showed excellent full spectrum (UV, visible, and NIR lights)-induced photocatalytic CO2 reduction performance directly from the air at ambient pressure. Particularly, after 4 h near-infrared light irradiation, ca. 4.32% CO2 in the air could be converted into CH3OH with 98.35% selectivity for Rb0.33WO3. The experiments and theoretical calculations unveiled that the introduced alkali metal atom occupied the tunnel of hexagonal structure and donated more free electrons to reco...

Evaluation of Oxidative Species in Gaseous and Liquid Phase Generated by Mini-Gliding Arc Discharge

Abstract: The gliding arc discharge plasma reactors are known as a source of non-equilibrium plasma at atmospheric pressure. In the present study, generation of dominant reactive oxygen and nitrogen species in gaseous and liquid phase in water by the compact gliding arc device (mini-GAD) and corresponding bactericidal effects were investigated. Water and phosphate buffer solutions were used as model liquids. Mini-GAD is a strong source of nitrogen oxides (up to 800 ppm NO and 200 ppm NO2) that result in high concentrations of nitrites and nitrates in water solutions. The highest bactericidal efficacy towards Escherichia coli was achieved for non-buffered water solution.

Effect of processing on high-velocity water vapor recession behavior of Yb-silicate environmental barrier coatings

Abstract: The purpose of this research was to investigate the corrosion behavior of the low/high Yb2SiO5 containing Yb2Si2O7 coatings under high-velocity water vapor flow. To that end, Yb2Si2O7 and Si coatings were deposited by atmospheric plasma spraying on SiC substrates. The corrosion tests were performed in the burned natural gas under atmospheric pressure, with a gas flow velocity of 100 m/s at 1200 °C for 200 h. After the test, a 25 μm thick, porous corrosion layer at the surface of the Yb2Si2O7 rich coatings was found accompanied with a mass reduction, whereas samples with Yb2SiO5 rich coatings showed mass gain indicating the greater resistance of Yb2SiO5 against water vapor. A comparison of the Yb2Si2O7 rich coatings tested in this work and Yb2Si2O7 bulk samples tested in an earlier work at the same facility revealed significantly different recession rates. Possible mechanisms responsible for this distinct behavior are discussed in the manuscript.

Large Earthquake Reshapes the Groundwater Flow System: Insight From the Water‐Level Response to Earth Tides and Atmospheric Pressure in a Deep Well

Abstract: Quantitative evaluation of earthquake‐induced permeability changes is important for understanding key geological processes, such as advective transport of heat and solute and the generation of elevated fluid pressure. Many studies have independently documented permeability changes in either an aquifer or an aquitard, but the effects of an earthquake on both the aquifer and aquitard of the same aquifer system are still poorly understood. In this study, we use the well water‐level response to earth tides and atmospheric pressure to study the changes in hydraulic properties in an aquifer and an overlying confining layer in Beijing, China, following the 11 March 2011 Tohoku earthquake in Japan. Our results show that both the tidal response amplitude and the phase shift increased and that the phase shift changed from negative to positive after the earthquake. We identified increased permeability in both the aquifer and aquitard by the barometric response function method. The horizontal transmissivity of the aquifer increased by a factor of 6, and the vertical diffusivity of the aquitard doubled.

High-Sensitivity Gas Pressure Fabry–Perot Fiber Probe With Micro-Channel Based on Vernier Effect

Abstract: In this paper, we propose and demonstrate a gas pressure fiber probe with high sensitivity magnified by Vernier effect. The probe is composed of two cascaded Fabry–Perot interferometers based on a SMF–SOHST–OFC structure (SMF: single-mode fiber; SOHST: side-opened hollow silica tube; OFC: optical fiber column). The high-frequency CO2 laser drilling method for hollow silica tube can effectively maintain the transient balance of the air pressure inside and outside the cavity without destroying the reflective ends of the optical fibers. Experimental results show that the prepared fiber probe with the SOHST length of 375.2 μ m and column length of 247.3 μ m has high gas pressure sensitivity of 80.3 pm/kPa by demodulating Vernier envelope, and it has relatively low temperature cross-sensitivity of –1.33 kPa/°C. This sensor is highly sensitive and of compact size, which not only can be applied in gas pressure sensing but also has the potential for application in microfluidic detection.

Cold Atmospheric Pressure Nitrogen Plasma Jet for Enhancement Germination of Wheat Seeds

Abstract: The possibility to improve the germination characterization of the wheat seeds by cold atmospheric nitrogen plasma jet treatment was report. Spectroscopic measurements were performed to identify the constituent particles of a nitrogen atmospheric plasma jet. Spectroscopic measurements revealed that the particles with relatively high energy excited states exist inside the jet nozzle. During this study the cold atmospheric plasma parameters were set for attain the highest rate of the germination seeds. The nitrogen used in this system as carrier gas. The nitrogen cold atmospheric plasma operated at 14 l/min as a fixed flow rate. The operation of plasma jet at 14 l/min was represented the suitable plasma dose to enhancement the germination parameters. The N2 first positive system (N2 1+), N2 second positive system (N2 2+) and N2 ion first negative system (N2+ 1−) were represented the emission spectra observed inside the jet nozzle. The germination characteristics of wheat seeds have been significantly enhanced after cold atmospheric plasma treatment. The mean weight of fresh sprout was 823.82 mg for untreated seeds and increased to 1231.80, 1369.50 and 1342.46 mg for 2 min, 4 min, and 6 min treatments respectively. The effects of nitrogen cold atmospheric plasma jet on the growth parameter depended on exposure time.

Controlling Effects of Residual Deformation on Pore Pressure: A Loess Soil Case

Abstract: What the role of each phase medium plays and how their interactions do work should be essential problems to understand dynamic behaviours of soils. In order to disclose interactions between solid, water, and air phases of soils, we applied loess samples to analyse controlling effects of residual deformation on pore pressure based on three kinds of laboratory tests. We obtained the similarity and difference of mechanical behaviors of soil samples under different water contents and loading. Both process and cause of pore air/water pressures are independent of initial stress conditions or loadings. However, absolute values of pore water pressure depend on the confining pressure, whereas the pore air pressure is contrary. The uniformity of responding process and cause of pore pressure depend upon the interaction mechanism between solid particles and air/water media, but the different absolute values depend upon the permeability and compressibility of air/water.

Electric field evolution in a diffuse ionization wave nanosecond pulse discharge in atmospheric pressure air

Abstract: The time-resolved electric field in a fast ionization wave discharge in a diffuse nanosecond pulse discharge plasma in atmospheric pressure air is measured using the Electric Field Induced Second Harmonic (E-FISH) diagnostic. The electric field is placed on an absolute scale by calibration against a Laplacian field. At relatively low peak voltages, when the plasma is generated only near the pin high-voltage electrode, the electric field is measured ahead of the ionization wave during the entire voltage pulse, exhibiting a strong field enhancement compared to the Laplacian field, by about an order of magnitude. As the peak voltage is increased and the ionization wave traverses the laser beam, the electric field is measured both ahead of the wave and behind the ionization front, where the field drops rapidly due to the charge separation and plasma selfshielding. When the wave reaches the grounded electrode, the discharge transitions into a conduction phase in which the potential is redistributed within the gap. The electric field in the vicinity of the pin then increases again, following the applied voltage waveform for the rest of the pulse. The effective time resolution of the present measurements is 150 ps. Based on the single shot data, we find that the peak electric field in the wave front is moderately influenced by the applied voltage and varies between 160 to 210 kV/cm. This study demonstrates the viability of the E-FISH diagnostic for this class of atmospheric pressure discharges and paves the way for future in-depth studies of this particular problem.

Pressure-Retaining Sampler and High-Pressure Systems to Study Deep-Sea Microbes Under in situ Conditions

Abstract: The pelagic realm of the dark ocean is characterized by high hydrostatic pressure, low temperature, high-inorganic nutrients, and low organic carbon concentrations. Measurements of metabolic activities of bathypelagic bacteria are often underestimated due to the technological limitations in recovering samples and maintaining them under in situ environmental conditions. Moreover, most of the pressure-retaining samplers, developed by a number of different labs, able to maintain seawater samples at in situ pressure during recovery have remained at the prototype stage, and therefore not available to the scientific community. In this paper, we will describe a ready-to-use pressure-retaining sampler, which can be adapted to use on a CTD-carousel sampler. As well as being able to recover samples under in situ high pressure (up to 60 MPa) we propose a sample processing in equi-pressure mode. Using a piloted pressure generator, we present how to perform sub-sampling and transfer of samples in equi-pressure mode to obtain replicates and perform hyperbaric experiments safely and efficiently (with <2% pressure variability). As proof of concept, we describe a field application (prokaryotic activity measurements and incubation experiment) with samples collected at 3,000m-depth in the Mediterranean Sea. Sampling, sub-sampling, transfer, and incubations were performed under in situ high pressure conditions and compared to those performed following decompression and incubation at atmospheric pressure. Three successive incubations were made for each condition using direct dissolved-oxygen concentration measurements to determine the incubation times. Subsamples were collected at the end of each incubation to monitor the prokaryotic diversity, using 16S-rDNA/rRNA high-throughput sequencing. Our results demonstrated that oxygen consumption by prokaryotes is always higher under in situ conditions than after decompression and incubation at atmospheric pressure. In addition, over time, the variations in the prokaryotic community composition and structure are seen to be driven by the different experimental conditions. Finally, within samples maintained under in situ high pressure conditions, the active (16S rRNA) prokaryotic community was dominated by sequences affiliated with rare families containing piezophilic isolates, such as Oceanospirillaceae or Colwelliaceae. These results demonstrate the biological importance of maintaining in situ conditions during and after sampling in deep-sea environments.

Polymorphism of nanocrystalline TiO2 prepared in a stagnation flame: formation of the TiO2-II phase

Abstract: A metastable "high-pressure" phase known as α-PbO2-type TiO2 or TiO2-II is prepared via a single-step synthesis using a laminar premixed stagnation flame. Three other TiO2 polymorphs, namely anatase, rutile and TiO2-B phases, can also be obtained by tuning the oxygen/fuel ratio. TiO2-II is observed as a mixture with rutile under oxygen-lean flame conditions. To the best of our knowledge, this is the first time that this phase has been identified in flame-synthesised TiO2. The formation of TiO2-II in an atmospheric pressure flame cannot be explained thermodynamically and is hypothesised to be kinetically driven through the oxidation and solid-state transformation of a sub-oxide TiO2-x intermediate. In this scenario, rutile is nucleated from the metastable TiO2-II phase instead of directly from a molten/amorphous state. Mixtures containing three-phase heterojunctions of anatase, rutile, and TiO2-II nanoparticles as prepared here in slightly oxygen-lean flames might be important in photocatalysis due to enhanced electron-hole separation.

Control of electron dynamics, radical and metastable species generation in atmospheric pressure RF plasma jets by Voltage Waveform Tailoring

Abstract: Atmospheric pressure capacitively coupled radio frequency discharges operated in He/N2 mixtures and driven by tailored voltage waveforms are investigated experimentally using a COST microplasma reference jet and by means of kinetic simulations as a function of the reactive gas admixture and the number of consecutive harmonics used to drive the plasma. Pulse-type 'peaks'-waveforms, that consist of up to four consecutive harmonics of the fundamental frequency (f = 13.56 MHz), are used at a fixed peak-to-peak voltage of 400 V. Based on an excellent agreement between experimental and simulation results with respect to the DC self-bias and the spatio-temporal electron impact excitation dynamics, we demonstrate that Voltage Waveform Tailoring allows for the control of the dynamics of energetic electrons, the electron energy distribution function in distinct spatio-temporal regions of interest, and, thus, the generation of atomic nitrogen as well as helium metastables, which are highly relevant for a variety of technological and biomedical applications. By tuning the number of driving frequencies and the reactive gas admixture, the generation of these important species can be optimised. The behaviour of the DC self-bias, which is different compared to that in low pressure capacitive radio frequency plasmas, is understood based on an analytical model.

Disrupting the spatio-temporal symmetry of the electron dynamics in atmospheric pressure plasmas by voltage waveform tailoring.

Abstract: Single frequency, geometrically symmetric Radio-Frequency (rf) driven atmospheric pressure plasmas exhibit temporally and spatially symmetric patterns of electron heating, and consequently, charged particle densities and fluxes. Using a combination of phase-resolved optical emission spectroscopy and kinetic plasma simulations, we demonstrate that tailored voltage waveforms consisting of multiple rf harmonics induce targeted disruption of these symmetries. This confines the electron heating to small regions of time and space and enables the electron energy distribution function to be tailored.

Modeling on Fragmentation of Clusters inside a Mass Spectrometer

Abstract: Atmospheric clusters are weakly bound and can fragment inside the measuring instruments, in particular, mass spectrometers. Since the clusters accelerate under electric fields, the fragmentation cannot be described in terms of rate constants under equilibrium conditions. Using basic statistical principles, we have developed a model for fragmentation of clusters moving under an external force. The model describes an energy transfer to the cluster internal modes caused by collisions with residual carrier gas molecules. As soon as enough energy is accumulated in the cluster internal modes, it can fragment. The model can be used for interpreting experimental measurements by atmospheric pressure interface mass spectrometers.

Highly Sensitive Determination of Arsenic and Antimony Based on an Interrupted Gas Flow Atmospheric Pressure Glow Discharge Excitation Source.

Abstract: A novel interrupted gas flow (IF) technique has been proposed for highly sensitive determination of ultratrace levels of arsenic and antimony in water samples by atmospheric pressure glow discharge...

The Transition to Paschen's Law for Microscale Gas Breakdown at Subatmospheric Pressure.

Abstract: The decrease in electronic device size necessitates greater understanding of gas breakdown and electron emission at microscale to optimize performance. While traditional breakdown theory using Paschen’s law (PL), driven by Townsend avalanche, fails for gap distance d $$\lesssim $$ 15 μm, recent studies have derived analytic equations for breakdown voltage when field emission and Townsend avalanche drive breakdown. This study derives a new analytic equation that predicts breakdown voltage VB within 4% of the exact numerical results of a previously derived theory and new experimental results at subatmospheric pressure for gap distances from 1–25 μm. At atmospheric pressure, VB transitions to PL near the product of pressure and gap distance, pd, corresponding to the Paschen minimum; at lower pressures, the transition to PL occurs to the left of the minimum. We further show that the work function plays a major role in determining which side of the Paschen minimum VB transitions to PL as pressure approaches atmospheric pressure while field enhancement and the secondary emission coefficient play smaller roles. These results indicate that appropriate combinations of these parameters cause VB to transition to PL to the left of the Paschen minimum, which would yield an extended plateau similar to some microscale gas breakdown experimental observations.

Study of Various Aqueous and Non-Aqueous Amine Blends for Hydrogen Sulfide Removal from Natural Gas

Abstract: Various novel amine solutions both in aqueous and non-aqueous [monoethylene glycol (MEG)/triethylene glycol(TEG)] forms have been studied for hydrogen sulfide (H2S) absorption. The study was conducted in a custom build experimental setup at temperatures relevant to subsea operation conditions and atmospheric pressure. Liquid phase absorbed H2S, and amine concentrations were measured analytically to calculate H2S loading (mole of H2S/mole of amine). Maximum achieved H2S loadings as the function of pKa, gas partial pressure, temperature and amine concentration are presented. Effects of solvent type on absorbed H2S have also been discussed. Several new solvents showed higher H2S loading as compared to aqueous N-Methyldiethanolamine (MDEA) solution which is the current industrial benchmark compound for selective H2S removal in natural gas sweetening process.

Thermoacoustic instability in a sequential combustor: Large eddy simulation and experiments

Abstract: This paper presents a large eddy simulation (LES) of a generic sequential combustor that was operated at atmospheric pressure and that features a thermoacoustic instability at 145 Hz. The full test rig consisting of a first stage plenum, burner and combustion chamber, of an air dilution section and of a sequential stage combustor was modeled. A compressible reactive 3-D LES was performed with semi-detailed chemistry accounting for different combustion modes which are all involved in the sequential combustor flame dynamics. These modes are flame propagation at ambient and elevated temperatures, and autoignition. The simulation is compared to experiments that featured hydroxide planar laser-induced fluorescence (OH-PLIF), OH* chemiluminescence optical diagnostics, and acoustic pressure measurements. Both flames show strong oscillatory dynamics that are remarkably well captured by the LES. The mode shape of the self-excited instability extracted from the LES pressure signals is also in very good agreement with the experiment. An analysis of the LES sequential flame dynamics shows that autoignition lengths in the mixing section are strongly modulated due to self-sustained out-of-phase oscillations of mixing temperature and axial velocity, which lead to strong oscillations of the reaction zone location.

Decomposition of Crystal Violet by an Atmospheric Pressure RF Plasma Jet: The Role of Radicals, Ozone, Near-Interfacial Reactions and Convective Transport

Abstract: Cold atmospheric pressure plasma (CAP) oxidizes organic compounds in water through the generation of a variety of reactive species including O3 and OH radicals. While the energy efficiency and rate of decomposition of the chemical compound in water is already extensively studied, only few studies focused on the reactive species responsible for the decomposition. We report on an investigation of the chemical reactive species involved in the decomposition of crystal violet (CV), a model organic compound, by an RF driven plasma jet in different gas mixtures. Different gas mixtures lead to different concentrations of reactive species responsible for the decolorization of CV. Moreover, the effect of transport limitations on the efficiency of the plasma treatment is reported. A study of positive control measurements, the effect of scavengers of relevant reactive species and particle imaging velocimetry reveal the dominant role of short-lived species at the plasma–liquid interface in which OH most likely plays an important role. Moreover, the decolorization rate is limited by transport of CV to the near boundary region. The results suggest that for the optimization of water treatment by the short-lived species generated by a plasma, an optimum transport of the to-be-treated compounds to the interface might be more critical than effective reactive species production in the plasma.

Hollow-Core Fiber-Based All-Fiber FPI Sensor for Simultaneous Measurement of Air Pressure and Temperature

Abstract: In paper, an all-fiber Fabry-Perot interferometer (FPI) sensor with cascaded micro-cavities is presented to measure air pressure and temperature simultaneously. The proposed sensor mainly consists of two tiny segments of hollow-core fiber (HCF) located at the end of lead-in single mode fiber (SMF), and there is a misalignment fusion splicing between the two HCFs with different core diameter. The sensor has minor length of about $210~\mu \text{m}$ since the two HCFs lengths are about $80~\mu \text{m}$ and $130~\mu \text{m}$ , respectively. Because the reflection spectrum of the sensor is formed by the fiber cavity, air cavity and their combined cavity, which can be processed by methods of fast Fourier transform (FFT) and Fourier band-pass filter (FBPF), so we can analyze the corresponding responses of every cavity from the reflection spectrum of sensor for temperature and pressure variations. The experiment results show that the sensor has not only two different linear temperature sensitivities but also two different linear pressure sensitivities, which can be used to distinguish air pressure and temperature simultaneously. The validity experiment shows the relative errors of 1.0% and 1.4% are obtained in simultaneous measurements of air pressure and temperature. The advantages of the presented sensor than other structure sensors are miniaturization, easier to manufacture and with lower fabrication cost, which is promising used in the harsh environment monitoring.