Showing papers on "Atmospheric pressure published in 1993"

Appearance of stable glow discharge in air, argon, oxygen and nitrogen at atmospheric pressure using a 50 Hz source

Abstract: Unusual glow discharges in air, argon, oxygen and nitrogen at atmospheric pressure can be produced using a 50 Hz source. This technique is introduced on the basis of the idea of a lower dielectric breakdown voltage gas. The electrode system, which is composed of a fine metal wire mesh of specified radius and a dielectric substance, is very useful for plasma surface processes and for chemical reactions in the plasma bulk. The observations of the Lissajous figure of voltage-electric charges and of the current pulse shapes are proposed as a method of distinguishing between the atmospheric pressure glow plasma and the silent electric discharge.

Measurement of the gas phase concentration of H2SO4 and methane sulfonic acid and estimates of H2SO4 production and loss in the atmosphere

Abstract: Measurements of gas phase sulfuric and methane sulfonic acid (MSA) have been performed using a relatively new atmospheric pressure selected ion chemical ionization mass spectrometric technique at two field sites. Both gas phase acids are photooxidation products, and their concentrations are seen to qualitatively follow solar flux. While sulfuric acid concentrations typically decline in conjunction with declining solar radiation, they sometimes level off in the mid 105–106 molecules cm−3 range after dark, even in relatively clean air. The reason for this quasi-stable nighttime sulfuric acid concentration is not well understood but may be a result of a steady state exchange of sulfuric acid between particles and the gas phase. Measurements of OH, H2SO4, and SO2 concentrations in conjunction with aerosol number and size distribution also made possible the independent calculation of gas phase sulfuric acid production and loss rates. Calculated production and loss rates are seen to agree well in relatively clean air during the daylight hours. At night, however, the sulfuric acid concentrations and its calculated loss rate often have a nonzero value. In more polluted air masses, calculated gas phase sulfuric acid losses significantly exceed calculated production if H2SO4/aerosol reaction probabilities of 1.0 or 0.5 are assumed.

Emission studies on a glow discharge in atmospheric pressure air using water as a cathode

Abstract: A stable discharge was produced in atmospheric air using water as a cathode. Spectral lines of elements dissolved in tap water could be observed. It is demonstrated that the appearance of these spectral lines is a consequence of cathode sputtering of water during the discharge. The intensity of the lines was found to depend strongly on the acidity of the water. This kind of discharge gives a possibility for continuous analysis of water and waste water solutions.

Pressure-induced enhancement of tc above 150 k in hg-1223.

Abstract: The recently discovered homologous series HgBa 2 Ca n -1 Cu n O 2 n +2+δ possesses remarkable properties. A superconducting transition temperature, T c , as high as 133 kelvin has been measured in a multiphase Hg-Ba-Ca-Cu-O sample and found to be attributable to the Hg-1223 compound. Temperature-dependent electrical resistivity measurements under pressure on a (> 95%) pure Hg-1223 phase are reported. These data show that T c increases steadily with pressure at a rate of about 1 kelvin per gigapascal up to 15 gigapascals, then more slowly and reaches a T c = 150 kelvin, with the onset of the transition at 157 kelvin, for 23.5 gigapascals. This large pressure variation (as compared to the small effects observed in similar compounds with the optimal T c ) strongly suggests that higher critical temperatures could be obtained at atmospheric pressure.

Simulations of the general circulation of the Martian Atmosphere: 2. Seasonal pressure variations

Abstract: The CO2 seasonal cycle of the Martian atmosphere and surface is simulated with a hybrid energy balance model that incorporates dynamical and radiation information from a large number of general circulation model runs. This information includes: heating due to atmospheric heat advection, the seasonally varying ratio of the surface pressure at the two Viking landing sites to the globally averaged pressure, the rate of CO2 condensation in the atmosphere, and solar heating of the atmosphere and surface. The predictions of the energy balance model are compared with the seasonal pressure variations measured at the two Viking landing sites and the springtime retreat of the seasonal polar cap boundaries. The following quantities are found to have a strong influence on the seasonal pressures at the Viking landing sites: albedo of the seasonal CO2 ice deposits, emissivity of this deposit, atmospheric heat advection, and the pressure ratio.

Stability and crystal structure of BC8 germanium.

Abstract: It is found that samples of crystalline germanium brought rapidly (1 s) to ambient pressure from 14 GPa transform to the so-called BC8 structure rather than to the ST12 structure that is found on slower pressure decrease. The BC8 phase is unstable at atmospheric pressure, but we have been able to record angle-dispersive powder patterns within less than 30 minutes of pressure release using an image-plate detector on a synchrotron source. The refined crystal structure of BC8-Ge is very similar to that found previously for BC8-Si.

Calculation of net emission coefficient of thermal plasmas in mixtures of gas with metallic vapour

Abstract: The net emission coefficient of Ar-Cu, N2-Cu, SF6-Cu and Ar-Fe mixtures was calculated for homogeneous and isothermal plasmas at atmospheric pressure in the temperature range between 3000 and 25000 K. The increase in power radiated due to the presence of metal vapours depends on the vapour itself (the net emission is higher with iron than with copper) and on the type of gas. The influence of pressure was calculated for the SF6-Cu mixture. In the last part of the paper the values of the net emission coefficient were used to calculate the temperature profile in stationary arc in Ar-Cu and N2-Cu mixtures. The influence of copper on radiation is preponderant on the temperature field at higher currents whereas the effect on electrical conductivity is important at lower currents.

Surface pressure field mapping using luminescent coatings

Abstract: In recent experiments we demonstrated the feasibility of using the oxygen dependence of luminescent molecules for surface pressure measurement in aerodynamic testing. This technique is based on the observation that for many luminescent molecules the light emitted increases as the oxygen partial pressure, and thus the air pressure, the molecules see decreases. In practice the surface to be observed is coated with an oxygen permeable polymer containing a luminescent molecule and illuminated with ultraviolet radiation. The airflow induced surface pressure field is seen as a luminescence intensity distribution which can be measured using quantitative video techniques. Computer processing converts the video data into a map of the surface pressure field. The experiments consisted of evaluating a trial luminescent coating in measuring the static surface pressure field over a two-dimensional NACA-0012 section model airfoil for Mach numbers ranging from 0.3 and 0.66. Comparison of the luminescent coating derived pressures were made to those obtained from conventional pressure taps. The method along with the experiment and its results will be described.

DC glow discharge in air flow at atmospheric pressure in connection with waste gases treatment

Abstract: The results of an experimental investigation of a DC glow discharge in fast air flow at a pressure of up to two atmospheres are presented. A high efficiency in the production of chemically active palticles is achieved in this kind of discharge. For dry air the ozone yield was as high as 80 g kwh" at a concentration of 0.05%. The resuits of a successful application of this discharge for SO2 and NO removal from polluted air are described. A full kinetic model for the glow discharge at atmospheric pressure of dry air has been developed which explains experimental results with satisfactory accuracy.

Pressure-Forced Seiches of Large Amplitude in Inlets of the Balearic Islands

Abstract: Large-amplitude harbor seiches usually occur in summer in the Balearic Islands. A significant correlation between sea level oscillations and atmospheric pressure disturbances has been found, though a proved physical mechanism to account for this atmosphere-ocean interaction is still missing. Using a flat bottom, shallow water model, we show that a direct coupling between atmospheric pressure and the free mode of an inlet is unlikely but that an oceanic wave of atmospheric origin can act as an intermediate mechanism and adequately force the inlet by resonance. The phase relationship derived from this mechanism is in good agreement with observations, provided the whole spectrum of oceanic waves is in opposite phase to the generating atmospheric disturbance. We also show that the very large oscillations observed at Ciutadella (an elongated, shallow inlet in the west coast of Menorca, Balearic Islands) can be explained in terms of the particular shape of this inlet.

Comparison of Experimental and Computed Species Concentration and Temperature Profiles in Laminar, Two-Dimensional Methane/Air Diffusion Flames

Abstract: Experimental concentration measurements of the major stable species and five radical species (OH., H atom, O atom, CH., and CH3) obtained on a rectangular Wolfhard-Parker slot burner are compared with a detailed computation of the chemical structure of an axisymmctric laminar, CH4/air diffusion flame burning at atmospheric pressure. In order to examine these CH4/air flames with different geometries and different sizes, the species profiles are plotted as functions of the local mixture fraction, and the scalar dissipation rate has been matched in a region around the stoichiometric surface. The overall agreement in the absolute concentrations, the shape of the profiles, and their location in terms of the local mixture fraction is good to excellent for the stable species (except for O2) and for the most abundant radicals OH, H atom, and O atom. For example, the calculated OH- maximum concentration is in much better agreement with the experimental results than are full equilibrium and partial equilib...

Effect of laser energy and atmosphere on the emission characteristics of laser-induced plasmas

Abstract: The effects of laser energy and atmosphere on the emission characteristics of laser-induced plasmas were studied with the use of a Q-switched Nd:YAG laser over a laser energy range of 20 to 95 mJ Argon, helium, and air were used as surrounding atmospheres, and the pressures were changed from atmospheric pressure to 1 Torr The experimental results showed that the maximum spectral intensity was obtained in argon at around 200 Torr at a high laser energy of 95 mJ, whereas the line-to-background ratio was maximized in helium at around 40 Torr at a low energy of 20 mJ The results are discussed briefly on the basis of the temporal and spatial observations of the laser-induced plasmas

Surface Characteristics of Wool and Poly ( ethylene Terephthalate) Fabrics and Film Treated with Low-Temperature Plasma Under Atmospheric Pressure

Abstract: Wool and poly ( ethylene terephthalate) fabrics and film were treated with low-tem perature plasmas of helium/argon or acetone/argon under atmospheric pressure for 10 to 180 seconds. Although argon...

Laser-Saturated Fluorescence Measurements of Nitric Oxide in Laminar, Flat, C2H6/O2/N2 Flames at Atmospheric Pressure

Abstract: We have performed both laser-saturated fluorescence (LSF) and linear laser-induced fluorescence (LIF) measurements of NO in lean and rich atmospheric-pressure C2H6/O2/N2 flames. Unlike previous LSF measurements of OH, NH, and CH, the LSF measurements of NO require a broadband detection scheme, and thus we include a comprehensive theory for broadband LSF. Saturation of NO is found to be easily attainable at atmospheric pressure. When high laser energies are used to insure saturation of NO, background fluorescence often occurs from additional flame species; hence, a subtraction technique is introduced to eliminate this fluorescence from the NO signal. Calibration of both the LSF and LIF techniques was accomplished by doping lean flames with known quantities of NO. A comparison of the LSF and LIF signals from postflame gases at ~ 1700 K as a function of equivalence ratio suggests that the influence of stoichiometry on fluorescence quenching is nearly negligible. Finally, we discuss the relative meri...

Mathematical model and laser‐scattering temperature measurements of a direct‐current plasma torch discharging into air

Abstract: The numerical plasma torch model of D. A. Scott, P. Kovitya, and G. N. Haddad [J. Appl. Phys. 66, 5232 (1989)], in which both the arc and plume regions are included in the computational domain, has been extended to treat the effect of the mixing of the plasma gas with the ambient gas. Both laminar diffusion and turbulent mixing are considered. The predictions of the model are compared with laser‐scattering measurements of the temperature distribution in the plume of a plasma torch, for the case in which the plasma gas is argon and the ambient gas is air at atmospheric pressure. Good agreement is found between the measurements and the predictions of the model. The rapid decay in plume temperature away from the exit of the torch nozzle is shown to be mainly due to cooling by air entrained by turbulent mixing. The K‐e turbulence model is found to adequately approximate the turbulence phenonema involved.

Destruction mechanisms for formaldehyde in atmospheric pressure low temperature plasmas

Abstract: Formaldehyde (CH2O) is a common pollutant of indoor air in residences and commercial buildings. The removal of CH2O from atmospheric pressure gas streams (N2/O2/H2O/CH2O) using plasmas generated by a dielectric barrier discharge has been theoretically investigated with the goal of cleansing indoor air. The model consists of a full accounting of the electron, ion, and neutral chemical kinetics in contaminated humid air. We find that the destruction of CH2O results dominantly from chemical attack by OH and O radicals, with the primary end products being CO and H2O. The predicted destruction rates for CH2O are typically 2–8 ppm/(mJ cm−3) (parts per million of CH2O in air/energy deposition). The elimination of the unwanted byproducts, CO and NO, using a platinum catalyst is discussed.

High pressure fuel feeding device for fuel injection engine

Abstract: A high pressure fuel/air injection system for an outboard motor having a V-cylinder arrangement wherein the major components of the air/fuel supply system are disposed in the valley between the cylinder banks. The system includes an vapor fuel separator that has a fuel chamber in which the supply of fuel is maintained by a float valve and an air chamber positioned above the fuel chamber and to one side of it and which communicates with the fuel chamber through a perforated member. A filter media fills the air chamber and an atmospheric air inlet is provided to the air chamber. Fuel pressure and fuel regulator valves are disposed in the area to the side of the air chamber and regulate fuel and air pressure by dumping fuel and air back to the fuel and air chambers, respectively, through integral internal conduits. The regulating system includes an arrangement for regulating the fuel pressure so that it will be at least greater than the air pressure by a predetermined amount and also for precluding the delivery of air under pressure if fuel under pressure is not supplied. The arrangement also incorporates a system for insuring that fuel cannot flow out of the atmospheric air inlet if the outboard motor is tilted up or is laid on its sides. An additional air supply is provided for the air compressor in the event the air chamber becomes clogged or inadequate to supply the air requirements for the system.

Atmospheric pressure ion interface for a mass analyzer

Abstract: A novel atmospheric pressure ionization device (10) for the transport of charged particle produced at atmospheric pressure to a mass analyzer (24) includes a liquid shield (60) between the particle source (22) and the sample inlet (66) into the mass analyzer. The analyzer is located in a high vacuum region (20) and an intermediate low vacuum region (18) is provided between the sample inlet and the analyzer. An ion optical system includes electrostatic lens assemblies (80) in said vacuum regions for transporting charged particles from the inlet to the analyzer.

Modeling radon transport in dry, cracked soil

Abstract: A two-dimensional finite element code was used to investigate the effect of changes in surface air pressure on radon flux from soil with parallel, partially penetrating cracks. A sensitivity analysis investigates the effects of various crack dimensions, soil characteristics, and surface air pressure on radon flux from the soil surface to the atmosphere. Simulation results indicate that radon flux is most sensitive to soil properties; the diffusion coefficient is most important, followed by permeability and porosity. Radon flux is also sensitive to changes in barometric pressure, which cause variations in radon flux above and below the average diffusive flux. Sinusoidal variations in barometric pressure cause a net increase in the average radon flux from the soil, because increases in flux during periods of decreasing pressure are greater than the decreases in flux during periods of decreasing pressure of equal magnitude. Cracks were found to significantly increase radon flux from soils of low permeability. 33 refs. 19 figs., 1 tab.

Nitric oxide production by lightning discharges

Abstract: We have investigated NO production in the expansion phase of a lightning discharge using a hydrodynamic model coupled with the chemical rate equations for the two Zel'dovich reactions and oxygen dissociation. We have found that most of the NO production occurs early in the discharge, prior to shock wave formation, and that the rapid drop in density, not temperature, controls NO formation. The number of molecules per Joule (P) depends strongly on the energy per unit volume in the initial heated channel: this dependence is nonlinear with a maximum value of 26 × 1016 molecules NO/J. For a representative discharge at a pressure of 1 atm, the number produced is 15 × 1016/J. Initial investigation indicates that for a constant energy density (estimated to be about 6 MJ/m3) the rate of production drops off rapidly with decreasing air density and thus altitude. Use of P appropriate for sea level pressure may lead to a major overestimate of the rate of NO formation in atmospheric lightning, much of which occurs at high altitude. We present suggestions for new laboratory experiments to quantify global NO production by lightning.

Dyeing Properties of Wool Treated with Low-Temperature Plasma Under Atmospheric Pressure

Abstract: Merino wool top was treated with low-temperature plasmas of helium/ argon and acetone/argon under atmospheric pressure for 30 seconds and then dyed with two leveling-type acid dyes, CI acid orange ...

Phase diagram and thermodynamic properties of solid magnesium in the quasiharmonic approximation.

Abstract: Using a family of volume-dependent interatomic pair potentials derived from first principles, we calculate phonon properties and thermodynamic functions in the quasiharmonic approximation for the hcp and bcc phases of Mg over a wide range of volume and temperature. At atmospheric pressure, the calculated hcp phonon-dispersion curves and thermodynamic properties agree well with experiment. The pressure dependence of the Raman-active transverse-optical phonon mode also agrees well with very recent measurements. At high pressure, the temperature dependence of the hcp-bcc phase line is predicted, with values of the transition pressure ranging from 52 GPa at zero temperature to about 28 GPa at 1000 K.

Boundary layer profiles in plasma chemical vapor deposition.

Abstract: A nonlinear optical spectroscopy based on degenerate four-wave mixing has made possible direct measurements of species temperature and concentration profiles through the boundary layer of a reactive plasma at atmospheric pressure. Spectra were obtained for CH and C_2 radicals over a range of conditions including those for the plasma chemical vapor deposition of diamond films. Numerical simulations based on a one-dimensional stagnation-point flow model are in good agreement with the measurements. The CH mole fraction is shown to rise and fall as a function of distance from the substrate, which is compelling experimental evidence for the complex chemistry that is occurring in the plasma boundary layer.

Sea Level Changes under Increasing Atmospheric CO2 in a Transient Coupled Ocean-Atmosphere GCM Experiment

Abstract: Climate change resulting from the enhanced greenhouse effect of increasing atmospheric CO2 concentrations is expected to bring about global and local changes in sea level. A global rise in sea level would result from thermal expansion of seawater and from melting of land ice, while changes in ocean dynamics and atmospheric pressure patterns could alter relative sea surface topography. Global and local sea level changes have been diagnosed from a 75-yr experiment with a version of the U.K. Meteorological Office coupled ocean-atmosphere general circulation model in which the CO2 concentration increases at 1% per year. Over the final decade, the component of mean global average sea level rise caused by thermal expansion is 90 mm; on this time scale, a significant contribution is expected from melting of mountain glaciers, but the model does not represent these. Sea level rises over practically the entire ocean area, but there is considerable variation in the magnitude, showing that the global figure...