Showing papers on "Atmospheric pressure published in 2015"

A porous metal-organic framework with ultrahigh acetylene uptake capacity under ambient conditions

Abstract: The efficient storage of high-energy gaseous fuels is problematic due to the risk of explosion. Here, the authors design and employ a metal-organic framework composed of Cu(II) and an octacarboxylate ligand, which is able to store acetylene in high density but at atmospheric pressure.

Electron density measurement in atmospheric pressure plasma jets: Stark broadening of hydrogenated and non-hydrogenated lines

Abstract: Electron density is one of the key parameters in the physics of a gas discharge. In this contribution the application of the Stark broadening method to determine the electron density in low temperature atmospheric pressure plasma jets is discussed. An overview of the available theoretical Stark broadening calculations of hydrogenated and non-hydrogenated atomic lines is presented. The difficulty in the evaluation of the fine structure splitting of lines, which is important at low electron density, is analysed and recommendations on the applicability of the method for low ionization degree plasmas are given. Different emission line broadening mechanisms under atmospheric pressure conditions are discussed and an experimental line profile fitting procedure for the determination of the Stark broadening contribution is suggested. Available experimental data is carefully analysed for the Stark broadening of lines in plasma jets excited over a wide range of frequencies from dc to MW and pulsed mode. Finally, recommendations are given concerning the application of the Stark broadening technique for the estimation of the electron density under typical conditions of plasma jets.

Development of a miniature mass spectrometer with continuous atmospheric pressure interface

Abstract: The demand for on-the-spot analysis is met by a miniature mass spectrometer which is preferred to be robust, stable, as small as possible and capable of analyzing different samples by coupling with various ionization methods. However, largely constrained by the atmospheric pressure interface (API), these aspects are difficult to be realized in one system. Herein, we describe the development of a new miniature mass spectrometer with balanced performance. The miniature mass spectrometer is small in size (30 × 30 × 18 cm) but has a continuous API, which was achieved by high-pressure ion trap operation and maximized ion transfer efficiency with the utilization of a differential pumping system. The miniature mass spectrometer was characterized and optimized in terms of stability, sensitivity, mass range, mass resolution and scan speed. Rapid analysis of mixtures was demonstrated by coupling the miniature mass spectrometer with the ambient ionization technique of paper spray. This is the smallest miniature mass spectrometer to date, which has a continuous API.

Effect of additive oxygen gas on cellular response of lung cancer cells induced by atmospheric pressure helium plasma jet.

Abstract: The atmospheric pressure helium plasma jet driven by pulsed dc voltage was utilized to treat human lung cancer cells in vitro. The properties of plasma plume were adjusted by the injection type and flow rate of additive oxygen gas in atmospheric pressure helium plasma jet. The plasma characteristics such as plume length, electric current and optical emission spectra (OES) were measured at different flow rates of additive oxygen to helium. The plasma plume length and total current decreased with an increase in the additive oxygen flow rate. The electron excitation temperature estimated by the Boltzmann plot from several excited helium emission lines increased slightly with the additive oxygen flow. The oxygen atom density in the gas phase estimated by actinometry utilizing argon was observed to increase with the additive oxygen flow. The concentration of intracellular reactive oxygen species (ROS) measured by fluorescence assay was found to be not exactly proportional to that of extracellular ROS (measured by OES), but both correlated considerably. It was also observed that the expression levels of p53 and the phospho-p53 were enhanced in the presence of additive oxygen flow compared with those from the pure helium plasma treatment.

CO2-CH4 conversion and syngas formation at atmospheric pressure using a multi-electrode dielectric barrier discharge

Abstract: The conversion of CO2 and CH4 into value-added chemicals is studied in a new geometry of a dielectric barrier discharge (DBD) with multi-electrodes, dedicated to the treatment of high gas flow rates. Gas chromatography is used to define the CO2 and CH4 conversion as well as the yields of the products of decomposition (CO, O2 and H2) and of recombination (C2H4, C2H6 and CH2O). The influence of three parameters is investigated on the conversion: the CO2 and CH4 flow rates, the plasma power and the nature of the carrier gas (argon or helium). The energy efficiency of the CO2 conversion is estimated and compared with those of similar atmospheric plasma sources. Our DBD reactor shows a good compromise between a good energy efficiency and the treatment of a large CO2 flow rate.

One-step Conversion of Furfural into 2-Methyltetrahydrofuran under Mild Conditions

Abstract: One-step direct conversion of biomass-derived furfural to 2-methyltetrahydrofuran was realized under atmospheric pressure over a dual solid catalyst based on two-stage-packed Cu-Pd in a reactor; this is the first report that one-step conversion of furfural resulted in high yield of 2-methyltetrahydrofuran (97.1 %) under atmospheric pressure. This strategy provided a successive hydrogenation process, which avoids high H2 pressure, uses the reactor efficiently, and eliminates the product-separation step. Therefore, it could enhance the overall efficiency as a result of low cost and high yield.

Explanation of penetration depth variation during laser welding under variable ambient pressure

Abstract: It has been observed that the penetration depth during laser welding (LW) under vacuum or reduced ambient pressure could be significantly greater than that during welding under atmospheric pressure. Previous explanations of this phenomenon usually limit to specific wavelength laser welding and have difficulties in explaining why the variation will disappear, as the welding speed increases. Here, we propose that this variation is caused by the temperature difference of keyhole wall under variable ambient pressure based on a correct physical description of related processes. A new surface pressure model, dependent on ambient pressure, is proposed for describing the evaporation process during laser material interaction under variable ambient pressure. For laser welding of a 304 stainless steel with 2.0 kW laser power and 3 m/min welding speed, it is shown that the average keyhole wall temperature is around 2900 K under atmospheric pressure, and only around 2300 K under vacuum, which results in significant penetration depth variations. Interestingly, it is also shown that as the welding speed increases, the average temperature of the front keyhole wall gradually rises due to the reduction of the mean incident angle of laser, and the magnitude of this increase is larger in welding under vacuum than under atmospheric pressure. It allows us to explain why the penetration depth improvement decreases to zero with the increase of welding speed.

Fiber-tip gas pressure sensor based on dual capillaries

Abstract: A micro-cavity fiber Fabry-Perot interferometer based on dual capillaries is proposed and demonstrated for gas pressure measurement. Such a device is fabricated by fusion splicing of a tiny segment of a main-capillary with a feeding-capillary on one end, and a single mode fiber on the other, to allow gas enters the main-capillary via the feeding-capillary. The reflection spectrum of the interferometer device shifts with the variation of gas pressure due to the dependence of gas refractive index on the pressure applied. During the device fabrication process, a core-offset fusion splicing method is adopted, which turns out to be highly effective for reducing the detection limit of the sensor. The experimental results obtained show that the proposed device exhibits a high gas pressure sensitivity of 4147 pm/MPa, a low temperature cross-sensitivity of less than 0.3 KPa/°C at atmospheric pressure, and an excellently low detection limit down to ~4.81 KPa. The robust tip structure, ultra-compact device size and ease of fabrication make the device an attractive candidate for reliable and highly sensitive gas pressure measurement in a precise location.

Optically pumped microplasma rare gas laser

Abstract: The optically pumped rare-gas metastable laser is a chemically inert analogue to three-state optically pumped alkali laser systems. The concept requires efficient generation of electronically excited metastable atoms in a continuous-wave (CW) electric discharge in flowing gas mixtures near atmospheric pressure. We have observed CW optical gain and laser oscillation at 912.3 nm using a linear micro-discharge array to generate metastable Ar(4s, 1s5) atoms at atmospheric pressure. We observed the optical excitation of the 1s5 → 2p9 transition at 811.5 nm and the corresponding fluorescence, optical gain and laser oscillation on the 2p10 ↔ 1s5 transition at 912.3 nm, following 2p9→2p10 collisional energy transfer. A steady-state kinetics model indicates efficient collisional coupling within the Ar(4s) manifold.

Effect of radical quenching on CH4/air flames in a micro flow reactor with a controlled temperature profile

Abstract: The effect of radical quenching on CH 4 /air flames was investigated using a micro flow reactor with a controlled temperature profile experimentally and numerically. To evaluate the radical quenching, two methods were employed in this study; changing the inner diameter of the reactor at atmospheric pressure, d ; and changing pressure in the reactor, P . The stabilized flame locations were measured and gas sampling analysis was conducted. The results were compared with two-dimensional computation including detailed gas-phase kinetics with/without a radical quenching surface reaction mechanism. At atmospheric pressure, there was no significant difference in the flame locations between the inert and quench wall cases at d = 2.0 and 1.5 mm. The measured flame location agreed with the computational flame locations. Thus the effect of radical quenching on the flame locations were negligible. The measured CO mole fraction agreed with the computed CO mole fraction for the inert wall, whereas significant amount of CO was predicted for the quench wall. At reduced pressures (0.5, 0.1 and 0.05 atm), the flame locations in computations for the inert wall fairly agreed with those in experiments. Flames blew out in computations for the quench wall with the sticking coefficient, S , of unity. The present surface reaction mechanism overestimated the effect of the radical quenching on flames. The equivalence ratio dependence of the CO mole fraction of burned gas was computed for the quench wall with S = 0.0005 at all pressures. When ϕ > 1, the effect of the radical quenching on the CO mole fraction was not significant at P = 0.5 atm but some effects were observed at P = 0.1 and 0.05 atm. When ϕ S = 0.0005. Reaction pathways of OH production by the interaction between gas-phase reactions and radical quenching surface reactions were identified for interpreting this CO oxidation enhancement.

Multistage oscillatory “Cool Flame” behavior for isolated alkane droplet combustion in elevated pressure microgravity condition

Abstract: Recently, large diameter, isolated n-heptane droplet experiments under microgravity conditions (aboard the International Space Station) exhibited “Cool Flame” burning behavior, resulting from a heat loss mechanism that extinguishes hot combustion and a transition into a sustained, low temperature second stage combustion. In atmospheric pressure air, a single combustion mode transition to “Cool Flame” burning is followed by diffusive extinction. But with increasing pressure, multiple cycles of hot initiation followed by transition to “Cool Flame” burning are observed. This paper reports experimental observations that characterize the transition time histories of this multi-cycle, multi-stage behavior. Transient sphero-symmetric droplet combustion modeling that considers multi-stage detailed kinetics, multi-component diffusion, and spectral radiation is applied to analyze the experimental observations. The simulations indicate that as parameters change the chemical time scales dictating low temperature degenerate chain branching, multiple hot/cool flame burning transitions are induced by increasing the cool flame burning heat generation rate compared to the diffusive loss rate. The balance of these terms in the negative temperature coefficient kinetic regime defines whether reactions accelerate into re-ignition of a hot flame event, burn quasi-steadily in the cool flame mode, or diffusively extinguish. The rate of reactions controlling ketohydroperoxide formation and destruction are shown to be key re-ignition of hot combustion from the cool flame mode. Predictions are found to be in good agreement with the experimental measurements. Modeling is further applied to determine how these observations are dependent on initial experimental conditions, including pressure, and diluent species.

An open port sampling interface for liquid introduction atmospheric pressure ionization mass spectrometry

Abstract: RATIONALE: A simple method to introduce unprocessed samples into a solvent for rapid characterization by liquid introduction atmospheric pressure ionization mass spectrometry has been lacking. The continuous flow, self-cleaning open port sampling interface introduced here fills this void. METHODS: The open port sampling interface used a vertically aligned, co-axial tube arrangement enabling solvent delivery to the sampling end of the device through the tubing annulus and solvent aspiration down the center tube and into the mass spectrometer ionization source via the commercial APCI emitter probe. The solvent delivery rate to the interface was set to exceed the aspiration rate creating a continuous sampling interface along with a constant, self-cleaning spillover of solvent from the top of the probe. RESULTS: Using the open port sampling interface with positive ion mode APCI and a hybrid quadrupole time of flight mass spectrometer, rapid, direct sampling and analysis possibilities are exemplified with plastics, ballpoint and felt tip ink pens, skin, and vegetable oils. These results demonstrated that the open port sampling interface could be used as a simple, versatile and self-cleaning system to rapidly introduce multiple types of unprocessed, sometimes highly concentrated and complex, samples into a solvent flow stream for subsequent ionization andmore » analysis by mass spectrometry. The basic setup presented here could be incorporated with any self-aspirating liquid introduction ionization source (e.g., ESI, APCI, APPI, ICP, etc.) or any type of atmospheric pressure sampling ready mass spectrometer system. CONCLUSIONS: The open port sampling interface provides a means to introduce and quickly analyze unprocessed solid or liquid samples with liquid introduction atmospheric pressure ionization source without fear of sampling interface or ionization source contamination.« less

Research Update: Atmospheric pressure spatial atomic layer deposition of ZnO thin films: Reactors, doping, and devices

Abstract: Atmospheric pressure spatial atomic layer deposition (AP-SALD) has recently emerged as an appealing technique for rapidly producing high quality oxides. Here, we focus on the use of AP-SALD to deposit functional ZnO thin films, particularly on the reactors used, the film properties, and the dopants that have been studied. We highlight how these films are advantageous for the performance of solar cells, organometal halide perovskite light emitting diodes, and thin-film transistors. Future AP-SALD technology will enable the commercial processing of thin films over large areas on a sheet-to-sheet and roll-to-roll basis, with new reactor designs emerging for flexible plastic and paper electronics.

Absolute OH density measurements in an atmospheric pressure dc glow discharge in air with water electrode by broadband UV absorption spectroscopy

Abstract: Spatially resolved absolute OH radical density measurements are performed in an atmospheric pressure glow discharge generated in ambient air with water electrode by broadband UV absorption spectroscopy. The radial distributions of OH density and gas temperature are obtained for the positive column, anode and cathode regions both for water-cathode and water-anode discharges. It is found that for both polarities of the water electrode the radial profiles of the ground state OH density and gas temperature are significantly broader than the total discharge emission intensity and the emission intensity originating from OH() only. Exceptional large OH densities exceeding 1023 m−3 are found. The OH kinetics are discussed in detail.

Measurements of 3D slip velocities and plasma column lengths of a gliding arc discharge

Abstract: A non-thermal gliding arc discharge was generated at atmospheric pressure in an air flow The dynamics of the plasma column and tracer particles were recorded using two synchronized high-speed cameras Whereas the data analysis for such systems has previously been performed in 2D (analyzing the single camera image), we provide here a 3D data analysis that includes 3D reconstructions of the plasma column and 3D particle tracking velocimetry based on discrete tomography methods The 3D analysis, in particular, the determination of the 3D slip velocity between the plasma column and the gas flow, gives more realistic insight into the convection cooling process Additionally, with the determination of the 3D slip velocity and the 3D length of the plasma column, we give more accurate estimates for the drag force, the electric field strength, the power per unit length, and the radius of the conducting zone of the plasma column

Mass spectrometry of atmospheric pressure plasmas

Abstract: Atmospheric pressure non-equilibrium plasmas (APPs) are effective source of radicals, metastables and a variety of ions and photons, ranging into the vacuum UV spectral region. A detailed study of these species is important to understand and tune desired effects during the interaction of APPs with solid or liquid materials in industrial or medical applications. In this contribution, the opportunities and challenges of mass spectrometry for detection of neutrals and ions from APPs, fundamental physical phenomena related to the sampling process and their impact on the measured densities of neutrals and fluxes of ions, will be discussed. It is shown that the measurement of stable neutrals and radicals requires a proper experimental design to reduce the beam-to-background ratio, to have little beam distortion during expansion into vacuum and to carefully set the electron energy in the ionizer to avoid radical formation through dissociative ionization. The measured ion composition depends sensitively on the degree of impurities present in the feed gas as well as on the setting of the ion optics used for extraction of ions from the expanding neutral-ion mixture. The determination of the ion energy is presented as a method to show that the analyzed ions are originating from the atmospheric pressure plasma.

High sensitivity piezoelectric sensors using flexible PZT thick-film for shock tube pressure testing

Abstract: With excellent electromechanical performance and flexibility, piezoelectric lead zirconate titanate (PZT) thick-film fabricated by tape-casting processing has been considered as sensing element in pressure sensor design. The use of flexible PZT thick-film in sensors makes it possible to withstand relatively large deformation or install onto curved surfaces such as those in pipeline pressure sensing, human pulse or heart rate monitor. In this paper, the performance of PZT thick-film pressure sensors is investigated, unimorph structure of pressure sensor was designed and fabricated, and the relationship between generated voltage signals to applied pressures of the model has been analyzed theoretically. Blast wave pressure test was conducted using shock tube setup to test its sensing ability in response to air pressure loading. Different sized sensors were tested and showed nearly linear relationship to blast pressure in the experimental conditions. The voltage sensitivities of the sensor samples tested are several times higher than a commercial pressure sensor.

Silicon-based quantum dots: synthesis, surface and composition tuning with atmospheric pressure plasmas

Abstract: The synthesis of silicon and silicon-based quantum dots (diameter < 5 nm) is discussed. Specifically the synthesis of Si-based quantum dots (QDs) by atmospheric pressure plasmas is reviewed and the most recent developments are also reported. Atmospheric pressure plasmas are then compared with other synthesis methods that include low pressure plasmas, wet chemistry, electrochemical etching and laser-based methods. Finally, progress in the synthesis of alloyed silicon QDs is discussed where the nanoscale Si–Sn and Si–C systems are reported. The report also includes a theoretical analysis that highlights some fundamental differences offered by plasmas at atmospheric pressure and that may provide opportunities for novel materials with advantageous properties.

Cancer therapy using non-thermal atmospheric pressure plasma with ultra-high electron density

Abstract: Cancer therapy using non-thermal atmospheric pressure plasma is a big challenge in plasma medicine. Reactive species generated from plasma are key factors for treating cancer cells, and thus, non-thermal atmospheric pressure plasma with high electron density has been developed and applied for cancer treatment. Various cancer cell lines have been treated with plasma, and non-thermal atmospheric plasma clearly has anti-tumor effects. Recent innovative studies suggest that plasma can both directly and indirectly affect cells and tissues, and this observation has widened the range of applications. Thus, cancer therapy using non-thermal atmospheric pressure plasma is promising. Animal experiments and understanding the mode of action are essential for clinical application in the future. A new academic field that combines plasma science, the biology of free radicals, and systems biology will be established.