Showing papers on "Atmospheric pressure published in 1995"
TL;DR: In this article, the role of atmospheric pressure is emphasized by giving formulas in which the absorption, frequency, and relative humidity are all scaled with respect to atmospheric pressure, and new, more readable and useful figures showing atmospheric absorption as a function of frequency, relative humidity, and atmospheric pressure are presented.
Abstract: This Letter is an extension of an earlier Letter by Bass et al., ‘‘Atmospheric absorption of sound: Update’’ [J. Acoust. Soc. Am. 88, 2019–2021 (1990)]. Errors in a formula for saturation vapor pressure are corrected, and an alternative, much simpler formula is given. The role of atmospheric pressure is emphasized by giving formulas in which the absorption, frequency, and relative humidity are all scaled with respect to atmospheric pressure. Also presented are new, more readable and useful figures showing atmospheric absorption as a function of frequency, relative humidity, and atmospheric pressure. The new figures make it possible to estimate accurately the absorption at any value of atmospheric pressure.
412 citations
TL;DR: In this paper, the viscosity, thermal conductivity and electrical conductivity of atmospheric pressure plasmas in the temperature range from 300 to 30,000 K were investigated.
Abstract: Calculated values of the viscosity, thermal conductivity and electrical conductivity of air and mixtures of air and argon, air and nitrogen, and air and oxygen at high temperatures are presented. In addition, combined ordinary, pressure, and thermal diffusion coefficients are given for the gas mixtures. The calculations, which assione local thermodynamic equilibrium, are performed for atmospheric pressure plasmas in the temperature range from 300 to 30,000 K. The results for air plasmas are compared with those of published theoretical and experimental studies. Significant discrepancies are found with the other theoretical studies; these are attributed to differences in the collision integrals used in calculating the transport coefficients. A number of the collision integrals used here are significantly more accurate than values used previously, resulting in more reliable values of the transport coefficients.
315 citations
TL;DR: In this paper, a model of a near-cathode layer is developed that is based on a multifluid description of the plasma and takes into account multiply charged ions, and the model is employed to calculate parameters of the layer as functions of the voltage drop in the layer and of the local value of the surface temperature.
Abstract: The paper deals with calculation of parameters in the near-cathode plasma layer, on the cathode surface and in the body of a cathode in high-pressure arc discharges. These parameters can be calculated independently of the arc column if the heat flux coming from the column to the edge of the near-cathode layer does not play a decisive role in the energy balance of the layer, which, according to the estimates presented, is a likely case. The physics of the near-cathode layer is reconsidered in view of major contradictions that have appeared in the literature recently, in particular with regard to the role of the near-cathode space charge sheath. A model of a near-cathode layer is developed that is based on a multifluid description of the plasma and takes into account multiply charged ions. The model is employed to calculate parameters of the layer as functions of the voltage drop in the layer and of the local value of the surface temperature. By means of these data, an approximate asymptotic theory of arc spots is extended to cathode spots in high-pressure plasmas. Calculated spot parameters are presented for the following combinations cathode/plasma: tungsten/argon, thoriated-tungsten/argon, thoriated-tungsten/nitrogen, and zirconium/nitrogen. The obtained results agree with the recent measurements of the spot temperature.
232 citations
TL;DR: In this article, the authors compared the characteristics of APG discharge with those of low-pressure plasma-enhanced CVD (LPPECVD) methods and found that the results were very similar.
Abstract: The synthesis of plasma-polymerized tetraethoxysilane (TEOS) and hexamethyldisiloxane (HMDSO) thin films by atmospheric pressure glow (APG) discharge was investigated and the characteristics of this method were compared with those of low-pressure plasma-enhanced CVD (LPPECVD) methods. The obtained films had smooth surfaces, no pinholes and uniform thicknesses. The qualities of the films analysed by FTIR and XPS, and emission spectra during the reaction, were very similar to those observed in the LPPECVD. The relationship between the substrate temperature and the deposition rate was strongly dependent on the presence of oxygen; the deposition rate increased with increases in the substrate temperature in the presence of oxygen. This behaviour is uniquely characteristic of the APG discharge process. This is because the gas-phase reaction of the monomer decompositions is enhanced by atomic oxygen, and the reaction rates in the gas phase increase as the gas-phase temperature increases.
213 citations
TL;DR: In this article, a process was optimized by varying the dilution, aging, organic modification, heat treatment and dip-coating conditions, allowing control of film porosity in the range ∼ 30-99%.
Abstract: Silica films with refractive indices in the range of 1.006 – 1.036 (equivalent porosity 98.5–91%) have been prepared at ambient pressure by a process wherein organo-siloxane polymers are deposited on a silicon substrate by conventional dip-coating at 25°C and 0.85 bar (atmospheric pressure in Albuquerque) and heating to 450°C. The film thicknesses (from scanning electron microscopy) vary from 0.1 to 3.5 μm, depending upon the dip-coating rate (0.05 – 1.9 cm/s) and concentration of the sol. The process was optimized by varying the dilution, aging, organic modification, heat treatment and dip-coating conditions, allowing control of film porosity in the range ∼ 30–99%. Imaging ellipsometry has been used to study the evolution of film porosity and thickness in situ. It is observed that the high porosity in these films is mainly attributable to dilation or ‘springback’ of the film during the final stage of drying.
176 citations
TL;DR: In this paper, a phenomenological analysis has been developed to relate the wetting efficiency with operating conditions such as reactor pressure, gas and liquid flow rate, which can be expressed by the following correlation: ƞ CE = 1.104 REL 1/3 1 + [( ΔP Z )/p L g] Ga L 1/9
157 citations
TL;DR: In this article, the metal-silicate partition coefficients of Ni and Co in a model C1 chondrite were determined at pressures ranging from 1.2 to 12.0 GPa and temperatures between 2123 and 2750 K.
149 citations
TL;DR: In this article, the sensitivity of the Martian atmospheric circulation to a number of poorly known or strongly varying parameters (surface roughness length, atmospheric optical depth, CO2 ice albedo, and thermal emissivity) is investigated through experiments performed with the Martian version of the atmospheric general circulation model of Laboratoire de Meteorologie Dynamique, with a rather coarse horizontal resolution (a grid with 32 points in longitude and 24 points in latitude).
Abstract: The sensitivity of the Martian atmospheric circulation to a number of poorly known or strongly varying parameters (surface roughness length, atmospheric optical depth, CO2 ice albedo, and thermal emissivity) is investigated through experiments performed with the Martian version of the atmospheric general circulation model of Laboratoire de Meteorologie Dynamique, with a rather coarse horizontal resolution (a grid with 32 points in longitude and 24 points in latitude). The results are evaluated primarily on the basis of comparisons with the surface pressure records of the Viking mission. To that end, the records are decomposed into long-period seasonal variations due to mass exchange with the polar caps and latitudinal redistribution of mass, and short-period variations due to transient longitudinally propagating waves. The sensitivity experiments include a 5-year control simulation and shorter simulations (a little longer than 1 year) performed with “perturbed” parameter values. The main conclusions are that (1) a change of horizontal resolution (twice as many points in each direction) mostly affects the transient waves, (2) surface roughness lengths have a significant impact on the near-surface wind and, as a matter of consequence, on the latitudinal redistribution of mass, (3) atmospheric dust optical depth has a significant impact on radiative balance and dynamics, and (4) CO2 ice albedo and thermal emissivity strongly influence mass exchange between the atmosphere and the polar caps. In view of this last conclusion, an automatic procedure is implemented through which the albedo and emissivity of each of the two polar caps are determined, together with the total (i.e., including the caps) atmospheric CO2 content, in such a way as to get the closest fit of the model to the Viking pressure measurements.
147 citations
TL;DR: In this article, the effect of partial pressures of the reactants in the thermal de NOx process has been investigated in flow reactor experiments and two mechanisms for N2O formation in thermal deNOx have been identified.
123 citations
TL;DR: In this paper, the chemical structure of two premixed flames (n-decane and kerosene) were compared with a neat fuel, and the results showed that the n-Decane flame has a higher relative concentration of large alkyl radicals compared to the Kerosene flame.
Abstract: This study was aimed at comparing the chemical structure of two rich premixed flames Ted respectively with a neat fuel: n-decane and a multi-component fuel, kerosene. Both flames were stabilized on a flat-flame burner at atmospheric pressure. Samples were withdrawn along the symmetry axis with a quartz microprobe and analyzed by gas phase chromatography. The main objective was to justify, for a future modelling purpose, the use of a detailed reaction mechanism validated in the n-decane flame to predict the chemical structure of a kerosene flame. A close similitude was observed for the mole fraction profiles of both major species and main intermediates measured in each flame. Relative concentrations of the intermediate species in the n-decane flame can be interpreted qualitatively by β-scission of large alkyl radicals. The only marked difference observed when changing the fuel concerns benzene. The maximum mole fraction measured in the kerosene flame: 1.05·10−3 exceeds by one order of magnitude, t...
104 citations
TL;DR: In this article, the authors consider a system consisting of two parallel plates at different temperatures and place a solid network, e.g., a matrix or lattice, in the system, which partitions the space into very fine open pores.
Abstract: Consider a system consisting of two parallel plates at different temperatures. To reduce the heat transfer, one can place a solid network; e.g., a matrix or lattice, in the system. The matrix Partitions the space into very fine open pores. As a result, the motion of the gas molecules is restrict d and the heat transfer is reduced. Silica aerogel is a porous medium, which has pore sizes of about 10 nm, which is smaller than the mean free path of gas molecules at atmospheric pressure (about 80 nm) in a free space. Hence, even at atmospheric pressure the matrix restricts the motion of the gas molecules; the effect is more pronounced at lower pressures. 5 refs., 2 figs.
TL;DR: It is found that nonnative turn structures are formed prior to the appearance of the native secondary structure in the folding from the pressure-unfolded state, and there is a possibility that, for ribonuclease A, application of high pressure up to 570 MPa induces such a partially unfolded state as has native-like secondary structure but permits solvent to be highly accessible to the internal regions.
Abstract: Fourier transform infrared (FT-IR) spectroscopy combined with a resolution enhancement technique has been used to characterize pressure and thermal effects on the secondary structure of ribonuclease A. The experiments were performed at pD 7.0 with 50 mg/mL protein solution in D2O buffer. According to the observed changes in the amide I' band, secondary structure elements such as alpha-helices, beta-sheets, and turns are cooperatively disrupted by application of either pressures above 570 MPa at 30 degrees C or temperatures above 60 degrees C at 0.1 MPa. Pressure- and thermally-denatured ribonuclease A are fully unfolded and do not contain any residual secondary structures. Both the structural changes are intrinsically reversible, although the pressure-induced transition shows a hysteresis. It is found that nonnative turn structures are formed prior to the appearance of the native secondary structure in the folding from the pressure-unfolded state. The structural features upon the pressure-induced unfolding are additionally characterized by the interesting behavior of hydrogen-deuterium exchange at high pressure. Most of the backbone amide protons protected at atmospheric pressure, which are involved in the alpha-helices and beta-sheet, are exchanged with solvent deuterons in the pressure range where the two secondary structural elements are virtually identified as intact. There is a possibility that, for ribonuclease A, application of high pressure up to 570 MPa induces such a partially unfolded state as has native-like secondary structure but permits solvent to be highly accessible to the internal regions.
TL;DR: In this article, it has been shown that copolymerization causes the γ -phase to be generated at atmospheric pressure for high molecular weight polymers, and that the greater the amount of comonomer, the easier it is to form the polymeric phase.
TL;DR: In this paper, temperature profiles for various oxide-tungsten cathodes and for pure tungsten oxide cathodes are presented for high-current arcs burning in argon at atmospheric pressure.
Abstract: Measured temperature profiles for various oxide-tungsten cathodes and for pure tungsten cathodes are presented for high-current arcs burning in argon at atmospheric pressure. Temperature profiles are also presented for thoriated tungsten cathodes with different cathode cone angles, are currents and composition of the gas provided to the arc. Evidence is also presented that the temperature and the behaviour of the cathode are sensitive to the oxygen concentration in the argon.
TL;DR: In this paper, the authors measured the reflectance spectra of several Mars soil analog materials under low atmospheric pressures and temperatures. And they found that the 3-micrometer band remains a dominant feature and is especially broad in spectra for the ferrihydrite and palagonitic soil.
Abstract: Infrared reflectance spectra of carefully selected Mars soil analog materials have been measured under low atmospheric pressures and temperatures. Chemically altered montmorillonites containing ferrihydrite and hydrated ferric sulfate complexes are examined, as well as synthetic ferrihydrate and a palagonitic soil from Haleakala, Maui. Reflectance spectra of these analog materials exhibit subtle visible to near-infrared features, which are indicative of nanophase ferric oxides or oxyhydroxides and are similar to features observed in the spectra of the bright regions of Mars. Infrared reflectance spectra of these analogs include hydration features due to structural OH, bound H2O and adsorbed H2O. The spectal character of these hydration features is highly dependent on the sample environment and on the nature of the H2O/OH in the analogs. The behavior of the hydration features near 1.9 micrometers, 2.2 micrometers, 2.7 micrometers, 3 micrometers, and 6 micrometers are reported here in spetra measured under Marslike atmospheric environment. In spectra of these analogs measured under dry Earth atmospheric conditions the 1.9-micrometer band depth is 8-17%; this band is much stonger under moist conditions. Under Marslike atmospheric conditions the 1.9-micrometer feature is broad and barely discernible (1-3% band depth) in spectra of the ferrihydrite and palagonitic soil samples. In comparable spectra of the ferric sulfate-bearing montmorillonite the 1.9-micrometer feature is also broad, but stronger (6% band depth). In the low atmospheric pressure and temperature spectra of the ferrihydrite-bearing montmorillonite this feature is sharper than the other analogs and relatively stronger (6% band depth). Although the intensity of the 3- micrometer band is weaker in spectra of each of the analogs when measured under Marslike conditions, the 3-micromter band remains a dominant feature and is especially broad in spectra of the ferrihydrite and palagonitic soil. The structural OH features observed in these materials at 2.2-2.3 micrometers and 2.27 micrometers remain largely unaffected by the environmental conditions. A shift in the Christiansen feature towards shorter wavelengths has also been observed with decreasing atmospheric pressure and temperature in the midinfrared spectra of these samples.
TL;DR: In this article, the first measurements of the simultaneous adsorption of CO2 and H2O under conditions appropriate to the Martian regolith were made, and it was shown that CO2 does not substantially displace CO2, implying that the adsorbate inventories previously derived may be accurate.
Abstract: The Martian regolith is the most substantial volatile reservoir on the planet; estimates of its adsorbed inventory have been based on simple measurements of the adsorption of either water or CO2 in isolation. Under some conditions, H2O can poison adsorbate surfaces, such that CO2 uptake is greatly reduced. We have made the first measurements of the simultaneous adsorption of CO2 and H2O under conditions appropriate to the Martian regolith and have found that at H2O monolayer coverage above about 0.5, CO2 begins to be displaced into the gas phase. We have developed an empirical expression that describes our co-adsorption data and have applied it to standard models of the Martian regolith. We find that currently, H2O does not substantially displace CO2, implying that the adsorbate inventories previously derived may be accurate, not more than 3-4 kPa (30-40 mbar). No substantial increase in atmospheric pressure is predicted at higher obliquities because high-latitude ground ice buffers the partial pressure of H2O in the pores, preventing high monolayer coverages of H2O from displacing CO2. The peak atmospheric pressure at high obliquity does increase as the total inventory of exchangeable CO2 increases.
TL;DR: In this article, low-temperature photoluminescence (PL) in single-crystal GaN films grown on sapphire substrates by metalorganic chemical vapor deposition has been studied as a function of applied hydrostatic pressure using the diamond anvilcell technique.
Abstract: Low‐temperature photoluminescence (PL) in single‐crystal GaN films grown on sapphire substrates by metalorganic chemical vapor deposition has been studied as a function of applied hydrostatic pressure using the diamond‐anvil‐cell technique. The PL spectra of the GaN at atmospheric pressure were dominated by two sharp, strong, near‐band‐edge exciton luminescence lines and a broad emission band in the yellow spectral region. The exciton emission lines were found to shift almost linearly toward higher energy with increasing pressure. While the yellow emission band showed a similar blue shift behavior under applied pressure, a relatively strong sublinear pressure dependence was observed. By examining the pressure dependence of the exciton emission structures, the pressure coefficient of the direct Γ band gap in the wurtzite GaN was determined. The value of the hydrostatic deformation potential of the band gap has also been deduced from the experimental results.
TL;DR: In this paper, an experimental study of argon microwave discharges maintained by a surface wave at 2.45 GHz, at atmospheric pressure and under low flow, in a capillary tube is presented.
Abstract: This work presents an experimental study of argon microwave discharges maintained by a surface wave at 2.45 GHz, at atmospheric pressure and under low flow, in a capillary tube. Emission spectroscopy techniques are used to characterize these discharges. Special attention is paid to the determination of the electron temperature by using the line-to-continuum intensity ratio method. We show that, even in situations very close to local thermal equilibrium, simple substitution of the excitation temperature Texc by the electron temperature Te in the equation governing the line radiation emitted by a plasma should not be done. Causes for such an assertion are analysed and a parametric study is conducted to determine the sensitivity of the proposed method. This method is then applied to provide Te from experimental data corresponding to an atmospheric pressure argon plasma produced by a surface microwave.
TL;DR: In this paper, the surface reaction mechanisms and rate parameters applicable under practical conditions of catalytic combustion were derived from experimental studies of premixed hydrogen-air mixtures impinging on the surface of a heated platinum plate.
TL;DR: In this paper, experimental results on electron beam and pulsed corona processing of atmospheric-pressure gas streams containing dilute concentrations of carbon tetrachloride (CCl4) are presented.
TL;DR: A series of experiments in sea water at different hydrostatic pressures (from 1 to 300 bar) was carried out on some stainless steels containing different amounts of Cr, Ni, and Mo to investigate whether these elements and the hydrostatic pressure could affect the composition of tlte corrosion layer formed in seawater and the resistance of the steel to localised corrosion as mentioned in this paper.
Abstract: A series of experiments in sea water at different hydrostatic pressures (from 1 to 300 bar) was carried out on some stainless steels containing different amounts of Cr, Ni, and Mo to investigate whether these elements and the hydrostatic pressure could affect the composition of tlte corrosion layer formed in sea water and the resistance of the steel to localised corrosion. Electrochemical tests and X-ray photoelectron spectroscopy were used. The resistance to both localised and general corrosion was affected by the composition of the passive films. The resistance to localised corrosion of stainless steels at atmospheric pressure was improved by Mo, but lowered at high pressure. However, the presence of Ni improved the corrosion resistance of stainless steels at high pressure.
TL;DR: The observed compression rate under pressure and the partial irreversibility of cell compression after return to atmospheric pressure lead to the conclusion that a mass transfer between cell and cultivation medium occurred.
TL;DR: In this paper, two metastable phases of BaSi2 were synthesized under high pressure and high temperature conditions, and the electrical resistivity and the dominant carrier of these two phases were measured at atmospheric pressure and temperature from 80 to 290 K.
TL;DR: In this article, a comparison between numerical and experimental determination of the velocity profile of an ionizing front (primary streamer) in a DC positive point-to-plane corona discharge in dry air at atmospheric pressure is devoted to the comparison between simulation and experiment.
Abstract: The present work is devoted to the comparison between numerical and experimental determination of the velocity profile of an ionizing front (primary streamer) in a DC positive point-to-plane corona discharge in dry air at atmospheric pressure The inception and propagation of the ionizing front is simulated by a one-dimensional model, using finite differences in a flux-corrected transport numerical scheme, including gamma -effects, and using experimental results concerning the swarm parameters This model provides the spatio-temporal local field and charge density variations as well as the ionization front velocity An optical measurement of the velocity is performed with the same discharge parameters, using a photomultiplier and a single-slit device The technique is based on the experimental fact that, for a 1 cm gap in the 7-9 kV voltage range, the successive primary streamers corresponding to a given gap voltage display identical velocity profiles As a result of the comparison, it appears that a precise coupling between simulation and experiment is possible There is a voltage range (8-9 kV) within which good agreement is observed The front velocity in most of the gap is about 2*107 cm s-1 and the profile presents an increase when the streamer leaves the point electrode and when it reaches the cathode The possible mechanisms of these accelerations are discussed The model may be applied to a large variation range for various parameters such as the nature of the gas, pressure, inter-electrode gap and curvature radius of the active electrode
TL;DR: In this article, the authors show that simple heuristic modifications to the Schwarzschild analytical grey gas model (SGM) resolve these deficiencies, at least the catastrophic ones, including the addition of a spectral window, and allowing the scale height of optical depth to be different from that of the atmospheric pressure.
Abstract: Radiative equilibrium solutions are the starting point in our attempt to understand how the atmospheric composition governs the surface and atmospheric temperatures, and the greenhouse effect. The Schwarzschild analytical grey gas model (SGM) was the workhorse of such attempts. However, the solutions suffered from serious deficiencies when applied to Earth's atmosphere and were abandoned about 3 decades ago in favor of more sophisticated computer models. Here we show that simple heuristic modifications to the SGM resolve these deficiencies, at least the catastrophic ones. The modifications include the addition of a spectral window, as well as allowing the scale height of optical depth to be different from that of the atmospheric pressure. The modified SGM reveals the fundamental factors that govern the radiative equilibrium thermal structure. (1) The presence of a spectral window allows the temperature jump between the surface and the immediately overlying atmosphere to become small, irrespective of the magnitude of the surface temperature. (2) In an optically thick atmosphere (such as Earth and Venus), the surface temperature and the runaway greenhouse effect depend inversely (as the one-fourth power) on the Planck function-weighted width of the window and are independent of the optical depth and other atmospheric parameters. The vertical variation of temperature within the atmosphere, however, is determined by the vertical variation of optical depth. (3) The degree of convective instability of the radiative equilibrium thermal structure γ is proportional to the ratio H/Hτ, where H is the atmospheric scale height and Hτ is the scale height of the vertical variation of optical depth. Here, γ is the ratio of the radiative equilibrium lapse rate and the neutral lapse rate for dry convection; γ > 1 indicates that the profile is unstable to free convection. Thus Hτ < H emerges as one of the fundamental criteria for convective instability. These factors lead to several corollaries regarding the specific details of atmospheric thermal structure on Earth and Venus. For example, according to the modified SGM, the radiative equilibrium temperature profile is strongly superadiabatic in Earth's lower atmosphere because Hτ is dominated by the water vapor's scale height being much less (2 compared with 8 km) than the atmospheric scale height. In the case of Venus, the pressure broadening of the CO2 rotational lines makes Hτ a factor of 2 smaller than H. Some of these results have been obtained using more detailed, multispectral radiative equilibrium models.
TL;DR: In this paper, the authors used two types of discharge reactors, a dielectric barrier and a pulsed corona discharge reactor, to study the effects of gas temperature and electrical energy input on the decomposition chemistry and byproduct formation.
Abstract: Experiments are presented on the plasma‐assisted decomposition of dilute concentrations of methanol and trichloroethylene in atmospheric pressure air streams by electrical discharge processing. This investigation used two types of discharge reactors, a dielectric‐barrier and a pulsed corona discharge reactor, to study the effects of gas temperature and electrical energy input on the decomposition chemistry and byproduct formation. Our experimental data on both methanol and trichloroethylene show that, under identical gas conditions, the type of electrical discharge reactor does not affect the energy requirements for decomposition or byproduct formation. Our experiments on methanol show that discharge processing converts methanol to COx with an energy yield that increases with temperature. In contrast to the results from methanol, COx is only a minor product in the decomposition of trichloroethylene. In addition, higher temperatures decrease the energy yield for trichloroethylene. This effect may be due to...
TL;DR: In this article, the heterogeneous reactions of CF3OH with bulk liquid water and sulfuric acid solutions were studied in wetted-wall flow reactors with chemical ionization detection.
Abstract: The heterogeneous reactions of CF3OH with bulk liquid water and sulfuric acid solutions were studied in wetted-wall flow reactors with chemical ionization detection of CF3OH. Heterogeneous reaction probabilities (γ) increase strongly with increasing activity of water (e.g., γ = 4 × 10−4 on 60 wt% H2SO4 at 206 K and 8 × 10−2 on 40 wt% at 211 K). The heterogeneous loss of CF3OH was also studied on submicron sulfuric acid aerosol in an atmospheric pressure laminar flow reactor. The aerosol reaction probabilities increase linearly with increasing particle radius (r < 0.5 μm, 40 and 50 wt% sulfuric acid at 250 K), suggesting that CF3OH uptake is volume limited for stratospheric aerosol. These measurements indicate that CF3OH will have a lifetime of a few days in the troposphere due to its loss on cloud particles, but a much longer lifetime with respect to heterogeneous loss in the stratosphere.
TL;DR: In this article, a vacuum-atmosphere interface utilizing a cascade arc discharge was successfully demonstrated and a 175 keV electron beam was successfully propagated from vacuum through such a plasma interface and out into atmospheric pressure.
Abstract: Atmospheric pressure plasmas can be used to provide a vacuum‐atmosphere interface as an alternative to differential pumping. Vacuum‐atmosphere interface utilizing a cascade arc discharge was successfully demonstrated and a 175 keV electron beam was successfully propagated from vacuum through such a plasma interface and out into atmospheric pressure. Included in the article are a theoretical framework, experimental results, and possible applications for this novel interface.
TL;DR: In this paper, the importance of the different chemical pathways responible for NO x formation in lean-premixed combustion, and especially the role of the nitrous oxide pathway relative to the traditional Zeldovich pathway are discussed.
Abstract: This study addresses the importance of the different chemical pathways responible for NO x formation in lean-premixed combustion, and especially the role of the nitrous oxide pathway relative to the traditional Zeldovich pathway. NO x formation is modeled and computed over a range of operating conditions for the lean-premixed primary zone of gas turbine engine combustors. The primary zone, of uniform fuel-air ratio, is modeled as a micromixed well-stirred reactor, representing the flame zone, followed by a series of plug flow reactors, representing the postflame zone. The fuel is methane. The fuel-air equivalence ratio is varied from 0.5 to 0.7. The chemical reactor model permits study of the three pathways by which NO x forms, which are the Zeldovich, nitrous oxide, and prompt pathways. Modeling is also performed for the well-stirred reactor alone. Three recently published, complete chemical kinetic mechanisms for the C1−C2 hydrocarbon oxidation and the NO x formation are applied and compared. Verification of the model is based on the comparison of its NO x output to experimental results published for atmospheric pressure jet-stirred reactors and for a 10 atm. porous-plate burner. Good agreement between the modeled results and the measurements is obtained for most of the jet-stirred reactor operating range. For the porous-plate burner, the model shows agreement to the NO x measurements within a factor of two, with close agreement occurring at the leanest and coolest cases examined. For lean-premixed combustion at gas turbine engine conditions, the nitrous oxide pathway is found to be important, though the Zeldovich pathway cannot be neglected. The prompt pathway, however, contributes small-to-negligible NO x . Whenever the NO x emission is in the 15 to 30 ppmv (15 percent O 2 , dry) range, the nitrous oxide pathway is predicted to contribute 40 to 45 percent of the NO x for high-pressure engines (30 atm), and 20 to 35 percent of the NO x for intermediate pressure engines (10 atm). For conditions producing NO x of less than 10 ppmv (15 percent O 2 , dry), the nitrous oxide contribution increases steeply and approaches 100 percent. For lean-premixed combustion in the atmospheric pressure jet-stirred reactors, different behavior is found. All three pathways contribute; none can be dismissed. No universal behavior is found for the pressure dependence of the NO x . It does appear, however, that lean-premixed combustors operated in the vicinity of 10 atm have a relatively weak pressure dependence, whereas combustors operated in the vicinity of 30 atm have an approximately square root pressure dependence of the NO x
TL;DR: The effects of pressure on reactant conversion and product selectivities in three catalytic oxidation systems have been examined at pressures between 1 and > 5 atm in this article, and the results strongly suggest that free radical homogeneous chain reactions are not significant in these processes and that they can be operated reliably above atmospheric pressure.
Abstract: The effects of pressure on reactant conversion and product selectivities in three catalytic oxidation systems have been examined at pressures between 1 and > 5 atm Reaction was sustained autothermally near adiabatic operating conditions at temperatures of ∼1000°C with residence times over the noble metal catalysts between 10−4 and 10−2 s The three systems investigated were (1) HCN synthesis over Pt-10% Rh gauze catalysts, (2) methane oxidation to synthesis gas (CO and H2) over rhodium-coated monoliths, and (3) ethane conversion to ethylene over platinum-coated monoliths We find that selectivities in all three reactions do not change dramatically with approximately a five-fold increase in pressure This strongly suggests that free radical homogeneous chain reactions are not significant in these processes and that they can be operated reliably above atmospheric pressure For the synthesis of HCN over Pt-10% Rh gauzes, the selectivity to HCN can be maintained above 075 at pressures up to 55 atm Selectivities to synthesis gas (CO and H2) from a methane-air mixture over a Rh-coated foam monolith at pressures up to 55 atm were maintained above 090 Over a Pt-coated foam monolith, the selectivity to ethylene from ethane-air and ethane-O2 mixtures was independent of pressure up to 65 atm and conversion rose slightly although it was necessary to maintain constant velocity and residence time over the catalyst to avoid carbon formation