Showing papers on "Atmospheric pressure published in 2004"

Non-Equilibrium Air Plasmas at Atmospheric Pressure

Abstract: Atmospheric-pressure plasmas continue to attract considerable research interest due to their diverse applications, including high power lasers, opening switches, novel plasma processing applications and sputtering, EM absorbers and reflectors, remediation of gaseous pollutants, excimer lamps, and other noncoherent light sources. Atmospheric-pressu

Characterization of Gas Diffusion Layers for PEMFC

Abstract: In proton-exchange membrane fuel cells (PEMFC), gas diffusion layers serve as current collectors that allow ready access of fuel and oxidant to the anode and the cathode catalyst surfaces, respectively. Critical properties of five commercial and one in-house gas diffusion layers have been characterized and compared to determine factors limiting the oxygen transport in the cathode gas diffusion layer where there is no oxygen consumption. These properties are the limiting current, electronic resistivity, fraction of hydrophobic pores, gas permeability, pore size distribution, and surface morphology. Polarization curves using air and neat oxygen were collected to determine the air-limiting currents at three operating conditions: 80°C/75% relative humidity (RH) cathode inlet, 100°C/70% RH cathode inlet, and 120°C/35% RH cathode inlet, all at atmospheric pressure. Linear empirical relationships for permeability coefficient vs. limiting current were found at all three conditions. Characterization of the gas diffusion layers by porosimetry measurement provides the pore size distribution for the gas diffusion layers, which helps in understanding the correlation between the permeability coefficient and the limiting current at the temperatures and relative humidity tested. © 2004 The Electrochemical Society. All rights reserved.

Atmospheric pressure ion source

Abstract: A non-radioactive atmospheric pressure device for ionization of analytes comprises an atmospheric pressure chamber having an inlet for carrier gas, a first electrode (31) at one end, and a counter-electrode (32) at the other end of the chamber for creating an electrical discharge in the carrier gas thus creating metastable neutral excited-state species. Optionally, a grid (14) is provided to generate electrons or ions by contact with the excited-state species. The carrier gas containing the excited-state species or the electrons generated therefrom is directed at an analyte at atmospheric pressure near ground potential to form analyte ions.

Study of the atmospheric pressure loading signal in very long baseline interferometry observations

Abstract: [1] Redistribution of air masses due to atmospheric circulation causes loading deformation of the Earth's crust, which can be as large as 20 mm for the vertical component and 3 mm for horizontal components. Rigorous computation of site displacements caused by pressure loading requires knowledge of the surface pressure field over the entire Earth surface. A procedure for computing three-dimensional displacements of geodetic sites of interest using a 6 hourly pressure field from the National Centers for Environmental Prediction numerical weather models and the Ponte and Ray [2002] model of atmospheric tides is presented. We investigated possible error sources and found that the errors of our pressure loading time series are below the 15% level. We validated our model by estimating the admittance factors of the pressure loading time series using a data set of 3.5 million very long baseline interferometry observations from 1980 to 2002. The admittance factors averaged over all sites are 0.95 ± 0.02 for the vertical displacement and 1.00 ± 0.07 for the horizontal displacements. For the first time, horizontal displacements caused by atmospheric pressure loading have been detected. The closeness of these admittance factors to unity allows us to conclude that on average, our model quantitatively agrees with the observations within the error budget of the model. At the same time we found that the model is not accurate for several stations that are near a coast or in mountain regions. We conclude that our model is suitable for routine data reduction of space geodesy observations.

Atmospheric absorption in the atmosphere up to 160 km

Abstract: This paper describes new algorithms, not previously available, for predicting atmospheric absorption of sound at high altitudes. A basis for estimating atmospheric absorption up to 160 km is described. The estimated values at altitudes above 90 km must be considered as only approximate due to uncertainties about the composition of the atmosphere above 90 km and simplifying assumptions. At high altitudes, classical and rotational relaxation absorption are dominant, as opposed to absorption by molecular vibrational relaxation that is the principle atmospheric absorption loss mechanism for primary sonic booms propagating downward from a cruising supersonic aircraft. Classical and rotational relaxation absorption varies inversely with atmospheric pressure, thus increasing in magnitude at high altitudes as atmospheric pressure falls. However, classical and rotational losses also relax at the high values of frequency/pressure reached at high altitudes and thus, for audio and infrasonic frequencies, begin to dec...

Atmospheric-pressure plasma technology

Abstract: Major industrial plasma processes operating close to atmospheric pressure are discussed. Applications of thermal plasmas include electric arc furnaces and plasma torches for generation of powders, for spraying refractory materials, for cutting and welding and for destruction of hazardous waste. Other applications include miniature circuit breakers and electrical discharge machining. Non-equilibrium cold plasmas at atmospheric pressure are obtained in corona discharges used in electrostatic precipitators and in dielectric-barrier discharges used for generation of ozone, for pollution control and for surface treatment. More recent applications include UV excimer lamps, mercury-free fluorescent lamps and flat plasma displays.

Power consideration in the pulsed dielectric barrier discharge at atmospheric pressure

Abstract: Nonequilibrium, atmospheric pressure discharges are rapidly becoming an important technological component in material processing applications. Amongst their attractive features is the ability to achieve enhanced gas phase chemistry without the need for elevated gas temperatures. To further enhance the plasma chemistry, pulsed operation with pulse widths in the nanoseconds range has been suggested. We report on a specially designed, dielectric barrier discharge based diffuse pulsed discharge and its electrical characteristics. Two current pulses corresponding to two consecutive discharges are generated per voltage pulse. The second discharge, which occurs at the falling edge of the voltage pulse, is induced by the charges stored on the electrode dielectric during the initial discharge. Therefore, the power supplied to ignite the first discharge is partly stored to later ignite a second discharge when the applied voltage decays. This process ultimately leads to a much improved power transfer to the plasma.

Electrical and optical characterization of the plasma needle

Abstract: The plasma needle is a source to create a non-thermal radiofrequency plasma at atmospheric pressure. To improve the ease of working on biological samples, a flexible plasma probe was designed. In the new configuration, the needle was confined in a plastic tube through which helium flow was supplied. The new set-up was characterized by impedance measurements and emission spectroscopy. Impedance measurements were performed by means of an adjustable matching network; the results were modelled. The discharge was found to be entirely resistive; the measured voltage was in the range 140–270 Vrms and it was in excellent agreement with model results. From the resistance, the electron density was estimated to be 1017 m−3.Optical measurements showed substantial UV emission in the range 300–400 nm. Active oxygen radicals ( and ) were detected. Furthermore, the influence of helium flow speed was investigated. At low flow speeds, the density of molecular species in the plasma increased.UV emission and density of active species are important factors that determine the performance of plasma in the treatment of biological materials. Therefore, the new characterization will help us to understand and optimize the interactions of atmospheric plasma with cells and tissues.

A uniform glow discharge plasma source at atmospheric pressure

Abstract: An atmospheric-pressure, uniform, continuous, glow plasma was produced in ambient air assisted by argon feeding gas, using a 13.56 MHz rf source. Based on the measured current–voltage curve and optical emission spectrum intensity, the plasma showed typical glow discharge characteristics, free from streamers and arc. The measured rotational and vibrational temperatures were in the range of 490 to 630 K and 2000 to 3300 K, respectively, within the operation range of argon flow rate and rf power. From the spatial measurement of total optical emission intensity, and rotational and vibrational temperatures, the plasma shows very high uniformity (over 93%) in the lengthwise direction. The plasma size for this study was 200 mm×50 mm×5 mm, although a plasma was produced in the scaled-up version of 600 mm in length, aiming for large-area plasma applications.

Surface degradation and hydrophobic recovery of polyolefins treated by air corona and nitrogen atmospheric pressure glow discharge

Abstract: The surface degradation and production of low molecular weight oxidized materials (LMWOM) on bi- axially oriented polypropylene (BOPP) and low-density polyethylene (LDPE) films was investigated and compared for two different dielectric barrier discharge (DBD) treat- ment types, namely air corona and nitrogen atmospheric pressure glow discharge (N2 APGD). Contact angle mea- surements, X-ray photoelectron spectroscopy (XPS), and atomic force microscopy (AFM) analyses were performed in conjunction with rinsing the treated films in water. It is shown that N2 APGD treatments of both polyolefins result in much less surface degradation, therefore, allowing for a significantly higher degree of functionalization and better wettability. Hydrophobic recovery of the treated films has also been studied by monitoring their surface energy (s) over a period of time extending up to several months after treatment. Following both surface modification techniques, the treated polyolefin films were both found to undergo hydrophobic recovery; however, for N2 APGD modified surfaces, s ceases to decrease after a few days and attains a higher stable value than in the case of air corona treated films. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 1291-1303, 2004

Gas-Phase HO•-Initiated Reactions of Elemental Mercury: Kinetics, Product Studies, and Atmospheric Implications

Abstract: Mercury is an environmentally volatile toxic fluid metal that is assumed to have a long atmospheric residence time and hence is subject to long-range transport. The speciation and chemical transformation of mercury in the atmosphere strongly influences its bioaccumulation potential in the human food chain as well as its global cycling. To investigate the oxidation of Hg0 by HO•, the dominant daytime atmospheric oxidant, we performed kinetic and product studies over the temperature range 283−353 K under near atmospheric pressure (100 ± 0.13 kPa) in air and N2 diluents. Experiments were carried out by the relative rate method using five reference molecules and monitored by gas chromatography with mass spectroscopic detection (GC-MS). The HO• were generated using UV photolysis of isopropyl nitrite at 300 ≤ λ ≤ 400 nm in the presence of NO. The room-temperature rate constant was found to be (9.0 ± 1.3) × 10-14 cm3 molecule-1 s-1. The temperature dependence of the reaction can be expressed as a simple Arrheniu...

Effects of current limitation through the dielectric in atmospheric pressure glows in helium

Abstract: The influence of the dielectric barrier on the discharge regime of a uniform atmospheric pressure glow discharge is studied through fast, time-resolved imaging of the discharge optical emission and by a one-dimensional fluid model. The experiments show that the discharge regime can be adjusted over a wide range from a glow-like regime with a pronounced Faraday dark space and positive column to a Townsend-like discharge regime in which those features are absent. The determining factor for the discharge regime is the current limitation through the dielectric. Results of the one-dimensional fluid model confirm this observation. The fluid model also indicates that metastable helium atoms generated during a discharge pulse contribute significantly to the pre-ionization of the gas before the next breakdown through Penning ionization of nitrogen impurities.

Physics of high-pressure helium and argon radio-frequency plasmas

Abstract: The physics of helium and argon rf discharges have been investigated in the pressure range from 50 to 760Torr. The plasma source consists of metal electrodes that are perforated to allow the gas to flow through them. Current and voltage plots were obtained at different purity levels and it was found that trace impurities do not affect the shape of the curves. The electron temperature was calculated using an energy balance on the unbound electrons. It increased with decreasing pressure from 1.1 to 2.4eV for helium and from 1.1 to 2.0 for argon. The plasma density calculated at a constant current density of 138mA∕cm2 ranged from 1.7×1011 to 9.3×1011cm−3 for helium and from 2.5×1011 to 2.4×1012cm−3 for argon, increasing with the pressure. At atmospheric pressure, the electron density of the argon plasma is 2.5 times that of the helium plasma.

Deposition of thin organosilicon polymer films in atmospheric pressure glow discharge

Abstract: The atmospheric pressure glow discharge burning in nitrogen with small admixture of organosilicon compounds such as hexamethyldisilazane or hexamethyldisiloxane was used for the deposition of thin organosilicon polymer films. The properties of the discharge were studied by means of optical emission spectroscopy and electrical measurements. The deposited films were characterized by atomic force microscopy, x-ray photoelectron spectroscopy, infrared transmission measurements, ellipsometry, depth sensing indentation technique and contact angle measurements. The films were polymer-like, transparent in the visible range, with uniform thickness and without pinholes. The film hardness varied from 0.3 to 0.6 GPa depending on deposition conditions, the elastic modulus was in the range 15-28 GPa and the surface free energy was in the range 26-45 mJ m-2. The studied films exhibited good adhesion to the substrate.

Atmospheric pressure chemical vapour deposition of tungsten doped vanadium(IV) oxide from VOCl3, water and WCl6

Abstract: Thin films of thermochromic tungsten doped VO2 on glass substrates were prepared from the atmospheric pressure chemical vapour deposition (APCVD) reaction of VOCl3,·H2O and WCl6. X-Ray diffraction (XRD) and Raman spectroscopy indicated a solid solution V1−xWxO2 (x = 0.003–0.032). XPS studies indicated the tungsten was present as W4+. The thermochromic properties of the films were investigated by Raman, XRD and reflectance/transmission measurements. These indicated that incorporation of tungsten caused a reduction in the VO2 thermochromic switching temperature of 19 °C per W atom%. The thermochromic properties of the thin films show great potential for use as an intelligent window coating.

Sterilization of polymer foils with dielectric barrier discharges at atmospheric pressure

Abstract: The emission of UV light as well as chemical reaction in plasmas allow them to be used for decontamination of food packaging. Sterilization efficiency of different dielectric barrier discharge (DBD) setups at atmospheric pressure was investigated for spores of B. subtilis and A. niger sprayed onto PET foils. In normal DBDs the efficiency of spore reduction in different gases (nitrogen, argon, synthetic air) can be related to the UV spectra of these gases in the discharge. With special so-called cascaded dielectric barrier discharges (CDBDs) a fast reduction of viable cells by more than four orders of magnitude is possible within few seconds, even for UV resistant cells. The sealing properties of commonly used PE-PET-laminate can be maintained in CDBD which is not observed for single-gap DBD.

Atmospheric pressure of nitrogen plasmas in a ferroelectric packed bed barrier discharge reactor. Part I. Modeling

Abstract: Numerical modelling of ferroelectric packed bed nonthermal plasma reactor has been conducted to predict plasma parameters in a pure nitrogen environment. Simplified time averaged one-dimensional physical model based on Poisson's equation for electric field and transport equation for electrons was developed. The mean electron energy was obtained by a swarm relationship from calculated electric field profiles and plasma neutral conditions. For chemical model, N/sup +/, N/sub 2//sup +/, N/sub 3//sup +/, N/sub 4//sup +/, N/sup */, N/sub 2//sup */ and electron were considered where N/sup */ and N/sub 2//sup */ are the total excited atoms and molecules, respectively. The results show that all the plasma parameters increase with increasing applied AC voltage and pellet dielectric constant. The numerical results also show that the dominant ion is N/sub 4//sup +/ and the metastable molecule density is much higher than radical and the electron densities at atmospheric gas pressure.

Rotational, vibrational, and excitation temperatures of a microwave-frequency microplasma

Abstract: Integration of microplasma sources in portable systems sets constraints in the amount of power and vacuum levels employed in these plasma sources. Moreover, in order to achieve good power efficiency and prevent physical deterioration of the source, it is desirable to keep the discharge temperature low. In this paper, the thermal characteristics of an atmospheric argon discharge generated with a low-power microwave plasma source are investigated to determine its possible integration in portable systems. The source is based on a microstrip split-ring resonator and is similar to the one reported by Iza and Hopwood, 2003. Rotational, vibrational, and excitation temperatures are measured by means of optical emission spectroscopy. It is found that the discharge at atmospheric pressure presents a rotational temperature of /spl sim/300 K, while the excitation temperature is /spl sim/0.3 eV (/spl sim/3500 K). Therefore, the discharge is clearly not in thermal equilibrium. The low rotational temperature allows for efficient air-cooled operation and makes this device suitable for portable applications including those with tight thermal specifications such as treatment of biological materials.

Measurement of the sea-air DMS flux and transfer velocity using eddy correlation

Abstract: [1] We report the successful eddy-correlation (EC) measurement of dimethyl sulfide (DMS) fluxes using an atmospheric pressure ionization mass spectrometer (APIMS). Calculated hourly transfer velocities span the range of two widely used parameterizations. The results suggest that factors in addition to wind speed also control the flux, but some of the scatter in each wind speed interval is no doubt due to measurement uncertainties. We can at last measure the flux of a marine biogenic gas on a time scale of tens of minutes, with an accuracy of tens of percent. This enables investigations into the physical controls of air-sea gas transfer common to many important trace gas species.

Atmospheric and oceanic excitation of length-of-day variations during 1980–2000

Abstract: [1] Although nontidal changes in the Earth’s length-of-day on timescales of a few days to a few years are primarily caused by changes in the angular momentum of the zonal winds, other processes can be expected to cause the length-of-day to change as well. Here the relative contribution of upper atmospheric winds, surface pressure, oceanic currents, and ocean-bottom pressure to changing the length-of-day during 1980–2000 is evaluated using estimates of atmospheric angular momentum from the National Centers for Environmental Prediction/National Center for Atmospheric Research reanalysis project, estimates of the angular momentum of the zonal winds in the upper atmosphere from the United Kingdom Meteorological Office, and estimates of oceanic angular momentum from the Estimating the Circulation and Climate of the Ocean consortium’s simulation of the general circulation of the oceans. On intraseasonal timescales, atmospheric surface pressure, oceanic currents, and ocean-bottom pressure are found to be about equally important in causing the length-of-day to change, while upper atmospheric winds are found to be less important than these mechanisms. On seasonal timescales, the upper atmospheric winds are more important than the sum of currents and bottom pressure in causing the length-of-day to change and, except at the annual frequency, are even more important than surface pressure changes. On interannual timescales, oceanic currents and ocean-bottom pressure are found to be only marginally effective in causing the length-ofday to change. INDEX TERMS: 1223 Geodesy and Gravity: Ocean/Earth/atmosphere interactions (3339); 1239 Geodesy and Gravity: Rotational variations; 3319 Meteorology and Atmospheric Dynamics: General circulation; 4532 Oceanography: Physical: General circulation; KEYWORDS: Earth rotation, length-ofday, oceanic angular momentum